diff --git a/Cargo.lock b/Cargo.lock
index 0a795c502..21ae2b17f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1824,7 +1824,7 @@ checksum = "95505c38b4572b2d910cecb0281560f54b440a19336cbbcb27bf6ce6adc6f5a8"
 [[package]]
 name = "heed"
 version = "0.20.0-alpha.6"
-source = "git+https://github.com/meilisearch/heed?branch=put-current-with-data-codec#2824585c37a6c7c0c5d11fe13c0dad3ebb1a5c4f"
+source = "git+https://github.com/meilisearch/heed?branch=main#321b0d4f2d26ceb504e70b4cb4eac0e0bdb3d796"
 dependencies = [
  "bitflags 2.3.3",
  "bytemuck",
@@ -1842,16 +1842,19 @@ dependencies = [
 [[package]]
 name = "heed-traits"
 version = "0.20.0-alpha.6"
-source = "git+https://github.com/meilisearch/heed?branch=put-current-with-data-codec#2824585c37a6c7c0c5d11fe13c0dad3ebb1a5c4f"
+source = "git+https://github.com/meilisearch/heed?branch=main#321b0d4f2d26ceb504e70b4cb4eac0e0bdb3d796"
 
 [[package]]
 name = "heed-types"
 version = "0.20.0-alpha.6"
-source = "git+https://github.com/meilisearch/heed?branch=put-current-with-data-codec#2824585c37a6c7c0c5d11fe13c0dad3ebb1a5c4f"
+source = "git+https://github.com/meilisearch/heed?branch=main#321b0d4f2d26ceb504e70b4cb4eac0e0bdb3d796"
 dependencies = [
+ "bincode",
  "bytemuck",
  "byteorder",
  "heed-traits",
+ "serde",
+ "serde_json",
 ]
 
 [[package]]
@@ -2981,7 +2984,7 @@ dependencies = [
 [[package]]
 name = "lmdb-master-sys"
 version = "0.1.0"
-source = "git+https://github.com/meilisearch/heed?branch=put-current-with-data-codec#2824585c37a6c7c0c5d11fe13c0dad3ebb1a5c4f"
+source = "git+https://github.com/meilisearch/heed?branch=main#321b0d4f2d26ceb504e70b4cb4eac0e0bdb3d796"
 dependencies = [
  "cc",
  "doxygen-rs",
diff --git a/fuzzers/src/bin/fuzz-indexing.rs b/fuzzers/src/bin/fuzz-indexing.rs
index 1d53e069c..baf705709 100644
--- a/fuzzers/src/bin/fuzz-indexing.rs
+++ b/fuzzers/src/bin/fuzz-indexing.rs
@@ -113,7 +113,7 @@ fn main() {
                             index.documents(&wtxn, res.documents_ids).unwrap();
                             progression.fetch_add(1, Ordering::Relaxed);
                         }
-                        wtxn.abort().unwrap();
+                        wtxn.abort();
                     });
                     if let err @ Err(_) = handle.join() {
                         stop.store(true, Ordering::Relaxed);
diff --git a/index-scheduler/src/batch.rs b/index-scheduler/src/batch.rs
index 661285325..d53dbf001 100644
--- a/index-scheduler/src/batch.rs
+++ b/index-scheduler/src/batch.rs
@@ -32,7 +32,7 @@ use meilisearch_types::milli::heed::CompactionOption;
 use meilisearch_types::milli::update::{
     IndexDocumentsConfig, IndexDocumentsMethod, IndexerConfig, Settings as MilliSettings,
 };
-use meilisearch_types::milli::{self, Filter, BEU32};
+use meilisearch_types::milli::{self, Filter};
 use meilisearch_types::settings::{apply_settings_to_builder, Settings, Unchecked};
 use meilisearch_types::tasks::{Details, IndexSwap, Kind, KindWithContent, Status, Task};
 use meilisearch_types::{compression, Index, VERSION_FILE_NAME};
@@ -715,7 +715,7 @@ impl IndexScheduler {
 
                 // 2. Snapshot the index-scheduler LMDB env
                 //
-                // When we call copy_to_path, LMDB opens a read transaction by itself,
+                // When we call copy_to_file, LMDB opens a read transaction by itself,
                 // we can't provide our own. It is an issue as we would like to know
                 // the update files to copy but new ones can be enqueued between the copy
                 // of the env and the new transaction we open to retrieve the enqueued tasks.
@@ -728,7 +728,7 @@ impl IndexScheduler {
                 // 2.1 First copy the LMDB env of the index-scheduler
                 let dst = temp_snapshot_dir.path().join("tasks");
                 fs::create_dir_all(&dst)?;
-                self.env.copy_to_path(dst.join("data.mdb"), CompactionOption::Enabled)?;
+                self.env.copy_to_file(dst.join("data.mdb"), CompactionOption::Enabled)?;
 
                 // 2.2 Create a read transaction on the index-scheduler
                 let rtxn = self.env.read_txn()?;
@@ -766,7 +766,7 @@ impl IndexScheduler {
                     .map_size(1024 * 1024 * 1024) // 1 GiB
                     .max_dbs(2)
                     .open(&self.auth_path)?;
-                auth.copy_to_path(dst.join("data.mdb"), CompactionOption::Enabled)?;
+                auth.copy_to_file(dst.join("data.mdb"), CompactionOption::Enabled)?;
 
                 // 5. Copy and tarball the flat snapshot
                 // 5.1 Find the original name of the database
@@ -1106,7 +1106,7 @@ impl IndexScheduler {
         for task_id in &index_lhs_task_ids | &index_rhs_task_ids {
             let mut task = self.get_task(wtxn, task_id)?.ok_or(Error::CorruptedTaskQueue)?;
             swap_index_uid_in_task(&mut task, (lhs, rhs));
-            self.all_tasks.put(wtxn, &BEU32::new(task_id), &task)?;
+            self.all_tasks.put(wtxn, &task_id, &task)?;
         }
 
         // 4. remove the task from indexuid = before_name
@@ -1132,7 +1132,7 @@ impl IndexScheduler {
     /// The list of processed tasks.
     fn apply_index_operation<'i>(
         &self,
-        index_wtxn: &mut RwTxn<'i, '_>,
+        index_wtxn: &mut RwTxn<'i>,
         index: &'i Index,
         operation: IndexOperation,
     ) -> Result<Vec<Task>> {
@@ -1479,10 +1479,10 @@ impl IndexScheduler {
         }
 
         for task in to_delete_tasks.iter() {
-            self.all_tasks.delete(wtxn, &BEU32::new(task))?;
+            self.all_tasks.delete(wtxn, &task)?;
         }
         for canceled_by in affected_canceled_by {
-            let canceled_by = BEU32::new(canceled_by);
+            let canceled_by = canceled_by;
             if let Some(mut tasks) = self.canceled_by.get(wtxn, &canceled_by)? {
                 tasks -= &to_delete_tasks;
                 if tasks.is_empty() {
@@ -1530,14 +1530,14 @@ impl IndexScheduler {
             task.details = task.details.map(|d| d.to_failed());
             self.update_task(wtxn, &task)?;
         }
-        self.canceled_by.put(wtxn, &BEU32::new(cancel_task_id), &tasks_to_cancel)?;
+        self.canceled_by.put(wtxn, &cancel_task_id, &tasks_to_cancel)?;
 
         Ok(content_files_to_delete)
     }
 }
 
 fn delete_document_by_filter<'a>(
-    wtxn: &mut RwTxn<'a, '_>,
+    wtxn: &mut RwTxn<'a>,
     filter: &serde_json::Value,
     indexer_config: &IndexerConfig,
     must_stop_processing: MustStopProcessing,
diff --git a/index-scheduler/src/index_mapper/index_map.rs b/index-scheduler/src/index_mapper/index_map.rs
index a24213558..d250ba02a 100644
--- a/index-scheduler/src/index_mapper/index_map.rs
+++ b/index-scheduler/src/index_mapper/index_map.rs
@@ -5,8 +5,7 @@ use std::collections::BTreeMap;
 use std::path::Path;
 use std::time::Duration;
 
-use meilisearch_types::heed::flags::Flags;
-use meilisearch_types::heed::{EnvClosingEvent, EnvOpenOptions};
+use meilisearch_types::heed::{EnvClosingEvent, EnvFlags, EnvOpenOptions};
 use meilisearch_types::milli::Index;
 use time::OffsetDateTime;
 use uuid::Uuid;
@@ -309,7 +308,7 @@ fn create_or_open_index(
     options.map_size(clamp_to_page_size(map_size));
     options.max_readers(1024);
     if enable_mdb_writemap {
-        unsafe { options.flag(Flags::MdbWriteMap) };
+        unsafe { options.flags(EnvFlags::WRITE_MAP) };
     }
 
     if let Some((created, updated)) = date {
diff --git a/index-scheduler/src/lib.rs b/index-scheduler/src/lib.rs
index 896c06c99..545409b81 100644
--- a/index-scheduler/src/lib.rs
+++ b/index-scheduler/src/lib.rs
@@ -47,8 +47,9 @@ pub use features::RoFeatures;
 use file_store::FileStore;
 use meilisearch_types::error::ResponseError;
 use meilisearch_types::features::{InstanceTogglableFeatures, RuntimeTogglableFeatures};
-use meilisearch_types::heed::types::{OwnedType, SerdeBincode, SerdeJson, Str};
-use meilisearch_types::heed::{self, Database, Env, RoTxn, RwTxn};
+use meilisearch_types::heed::byteorder::BE;
+use meilisearch_types::heed::types::{SerdeBincode, SerdeJson, Str, I128};
+use meilisearch_types::heed::{self, Database, Env, PutFlags, RoTxn, RwTxn};
 use meilisearch_types::milli::documents::DocumentsBatchBuilder;
 use meilisearch_types::milli::update::IndexerConfig;
 use meilisearch_types::milli::{self, CboRoaringBitmapCodec, Index, RoaringBitmapCodec, BEU32};
@@ -64,8 +65,7 @@ use uuid::Uuid;
 use crate::index_mapper::IndexMapper;
 use crate::utils::{check_index_swap_validity, clamp_to_page_size};
 
-pub(crate) type BEI128 =
-    meilisearch_types::heed::zerocopy::I128<meilisearch_types::heed::byteorder::BE>;
+pub(crate) type BEI128 = I128<BE>;
 
 /// Defines a subset of tasks to be retrieved from the [`IndexScheduler`].
 ///
@@ -278,7 +278,7 @@ pub struct IndexScheduler {
     pub(crate) file_store: FileStore,
 
     // The main database, it contains all the tasks accessible by their Id.
-    pub(crate) all_tasks: Database<OwnedType<BEU32>, SerdeJson<Task>>,
+    pub(crate) all_tasks: Database<BEU32, SerdeJson<Task>>,
 
     /// All the tasks ids grouped by their status.
     // TODO we should not be able to serialize a `Status::Processing` in this database.
@@ -289,16 +289,16 @@ pub struct IndexScheduler {
     pub(crate) index_tasks: Database<Str, RoaringBitmapCodec>,
 
     /// Store the tasks that were canceled by a task uid
-    pub(crate) canceled_by: Database<OwnedType<BEU32>, RoaringBitmapCodec>,
+    pub(crate) canceled_by: Database<BEU32, RoaringBitmapCodec>,
 
     /// Store the task ids of tasks which were enqueued at a specific date
-    pub(crate) enqueued_at: Database<OwnedType<BEI128>, CboRoaringBitmapCodec>,
+    pub(crate) enqueued_at: Database<BEI128, CboRoaringBitmapCodec>,
 
     /// Store the task ids of finished tasks which started being processed at a specific date
-    pub(crate) started_at: Database<OwnedType<BEI128>, CboRoaringBitmapCodec>,
+    pub(crate) started_at: Database<BEI128, CboRoaringBitmapCodec>,
 
     /// Store the task ids of tasks which finished at a specific date
-    pub(crate) finished_at: Database<OwnedType<BEI128>, CboRoaringBitmapCodec>,
+    pub(crate) finished_at: Database<BEI128, CboRoaringBitmapCodec>,
 
     /// In charge of creating, opening, storing and returning indexes.
     pub(crate) index_mapper: IndexMapper,
@@ -730,9 +730,7 @@ impl IndexScheduler {
         if let Some(canceled_by) = &query.canceled_by {
             let mut all_canceled_tasks = RoaringBitmap::new();
             for cancel_task_uid in canceled_by {
-                if let Some(canceled_by_uid) =
-                    self.canceled_by.get(rtxn, &BEU32::new(*cancel_task_uid))?
-                {
+                if let Some(canceled_by_uid) = self.canceled_by.get(rtxn, &*cancel_task_uid)? {
                     all_canceled_tasks |= canceled_by_uid;
                 }
             }
@@ -983,7 +981,7 @@ impl IndexScheduler {
 
         // if the task doesn't delete anything and 50% of the task queue is full, we must refuse to enqueue the incomming task
         if !matches!(&kind, KindWithContent::TaskDeletion { tasks, .. } if !tasks.is_empty())
-            && (self.env.non_free_pages_size()? * 100) / self.env.map_size()? as u64 > 50
+            && (self.env.non_free_pages_size()? * 100) / self.env.info().map_size as u64 > 50
         {
             return Err(Error::NoSpaceLeftInTaskQueue);
         }
@@ -1009,7 +1007,7 @@ impl IndexScheduler {
         // Get rid of the mutability.
         let task = task;
 
-        self.all_tasks.append(&mut wtxn, &BEU32::new(task.uid), &task)?;
+        self.all_tasks.put_with_flags(&mut wtxn, PutFlags::APPEND, &task.uid, &task)?;
 
         for index in task.indexes() {
             self.update_index(&mut wtxn, index, |bitmap| {
@@ -1187,7 +1185,7 @@ impl IndexScheduler {
             | Err(Error::AbortedTask) => {
                 #[cfg(test)]
                 self.breakpoint(Breakpoint::AbortedIndexation);
-                wtxn.abort().map_err(Error::HeedTransaction)?;
+                wtxn.abort();
 
                 // We make sure that we don't call `stop_processing` on the `processing_tasks`,
                 // this is because we want to let the next tick call `create_next_batch` and keep
@@ -1208,7 +1206,7 @@ impl IndexScheduler {
                 let index_uid = index_uid.unwrap();
                 // fixme: handle error more gracefully? not sure when this could happen
                 self.index_mapper.resize_index(&wtxn, &index_uid)?;
-                wtxn.abort().map_err(Error::HeedTransaction)?;
+                wtxn.abort();
 
                 return Ok(TickOutcome::TickAgain(0));
             }
@@ -1354,7 +1352,7 @@ impl IndexScheduler {
 
 pub struct Dump<'a> {
     index_scheduler: &'a IndexScheduler,
-    wtxn: RwTxn<'a, 'a>,
+    wtxn: RwTxn<'a>,
 
     indexes: HashMap<String, RoaringBitmap>,
     statuses: HashMap<Status, RoaringBitmap>,
@@ -1469,7 +1467,7 @@ impl<'a> Dump<'a> {
             },
         };
 
-        self.index_scheduler.all_tasks.put(&mut self.wtxn, &BEU32::new(task.uid), &task)?;
+        self.index_scheduler.all_tasks.put(&mut self.wtxn, &task.uid, &task)?;
 
         for index in task.indexes() {
             match self.indexes.get_mut(index) {
diff --git a/index-scheduler/src/utils.rs b/index-scheduler/src/utils.rs
index 3971d9116..f4eff7ea5 100644
--- a/index-scheduler/src/utils.rs
+++ b/index-scheduler/src/utils.rs
@@ -3,9 +3,9 @@
 use std::collections::{BTreeSet, HashSet};
 use std::ops::Bound;
 
-use meilisearch_types::heed::types::{DecodeIgnore, OwnedType};
+use meilisearch_types::heed::types::DecodeIgnore;
 use meilisearch_types::heed::{Database, RoTxn, RwTxn};
-use meilisearch_types::milli::{CboRoaringBitmapCodec, BEU32};
+use meilisearch_types::milli::CboRoaringBitmapCodec;
 use meilisearch_types::tasks::{Details, IndexSwap, Kind, KindWithContent, Status};
 use roaring::{MultiOps, RoaringBitmap};
 use time::OffsetDateTime;
@@ -18,7 +18,7 @@ impl IndexScheduler {
     }
 
     pub(crate) fn last_task_id(&self, rtxn: &RoTxn) -> Result<Option<TaskId>> {
-        Ok(self.all_tasks.remap_data_type::<DecodeIgnore>().last(rtxn)?.map(|(k, _)| k.get() + 1))
+        Ok(self.all_tasks.remap_data_type::<DecodeIgnore>().last(rtxn)?.map(|(k, _)| k + 1))
     }
 
     pub(crate) fn next_task_id(&self, rtxn: &RoTxn) -> Result<TaskId> {
@@ -26,7 +26,7 @@ impl IndexScheduler {
     }
 
     pub(crate) fn get_task(&self, rtxn: &RoTxn, task_id: TaskId) -> Result<Option<Task>> {
-        Ok(self.all_tasks.get(rtxn, &BEU32::new(task_id))?)
+        Ok(self.all_tasks.get(rtxn, &task_id)?)
     }
 
     /// Convert an iterator to a `Vec` of tasks. The tasks MUST exist or a
@@ -88,7 +88,7 @@ impl IndexScheduler {
             }
         }
 
-        self.all_tasks.put(wtxn, &BEU32::new(task.uid), task)?;
+        self.all_tasks.put(wtxn, &task.uid, task)?;
         Ok(())
     }
 
@@ -169,11 +169,11 @@ impl IndexScheduler {
 
 pub(crate) fn insert_task_datetime(
     wtxn: &mut RwTxn,
-    database: Database<OwnedType<BEI128>, CboRoaringBitmapCodec>,
+    database: Database<BEI128, CboRoaringBitmapCodec>,
     time: OffsetDateTime,
     task_id: TaskId,
 ) -> Result<()> {
-    let timestamp = BEI128::new(time.unix_timestamp_nanos());
+    let timestamp = time.unix_timestamp_nanos();
     let mut task_ids = database.get(wtxn, &timestamp)?.unwrap_or_default();
     task_ids.insert(task_id);
     database.put(wtxn, &timestamp, &RoaringBitmap::from_iter(task_ids))?;
@@ -182,11 +182,11 @@ pub(crate) fn insert_task_datetime(
 
 pub(crate) fn remove_task_datetime(
     wtxn: &mut RwTxn,
-    database: Database<OwnedType<BEI128>, CboRoaringBitmapCodec>,
+    database: Database<BEI128, CboRoaringBitmapCodec>,
     time: OffsetDateTime,
     task_id: TaskId,
 ) -> Result<()> {
-    let timestamp = BEI128::new(time.unix_timestamp_nanos());
+    let timestamp = time.unix_timestamp_nanos();
     if let Some(mut existing) = database.get(wtxn, &timestamp)? {
         existing.remove(task_id);
         if existing.is_empty() {
@@ -202,7 +202,7 @@ pub(crate) fn remove_task_datetime(
 pub(crate) fn keep_tasks_within_datetimes(
     rtxn: &RoTxn,
     tasks: &mut RoaringBitmap,
-    database: Database<OwnedType<BEI128>, CboRoaringBitmapCodec>,
+    database: Database<BEI128, CboRoaringBitmapCodec>,
     after: Option<OffsetDateTime>,
     before: Option<OffsetDateTime>,
 ) -> Result<()> {
@@ -213,8 +213,8 @@ pub(crate) fn keep_tasks_within_datetimes(
         (Some(after), Some(before)) => (Bound::Excluded(*after), Bound::Excluded(*before)),
     };
     let mut collected_task_ids = RoaringBitmap::new();
-    let start = map_bound(start, |b| BEI128::new(b.unix_timestamp_nanos()));
-    let end = map_bound(end, |b| BEI128::new(b.unix_timestamp_nanos()));
+    let start = map_bound(start, |b| b.unix_timestamp_nanos());
+    let end = map_bound(end, |b| b.unix_timestamp_nanos());
     let iter = database.range(rtxn, &(start, end))?;
     for r in iter {
         let (_timestamp, task_ids) = r?;
diff --git a/index-scheduler/src/uuid_codec.rs b/index-scheduler/src/uuid_codec.rs
index 70a92ca94..54020fa3c 100644
--- a/index-scheduler/src/uuid_codec.rs
+++ b/index-scheduler/src/uuid_codec.rs
@@ -1,7 +1,7 @@
 use std::borrow::Cow;
 use std::convert::TryInto;
 
-use meilisearch_types::heed::{BytesDecode, BytesEncode};
+use meilisearch_types::heed::{BoxedError, BytesDecode, BytesEncode};
 use uuid::Uuid;
 
 /// A heed codec for value of struct Uuid.
@@ -10,15 +10,15 @@ pub struct UuidCodec;
 impl<'a> BytesDecode<'a> for UuidCodec {
     type DItem = Uuid;
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        bytes.try_into().ok().map(Uuid::from_bytes)
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        bytes.try_into().map(Uuid::from_bytes).map_err(Into::into)
     }
 }
 
 impl BytesEncode<'_> for UuidCodec {
     type EItem = Uuid;
 
-    fn bytes_encode(item: &Self::EItem) -> Option<Cow<[u8]>> {
-        Some(Cow::Borrowed(item.as_bytes()))
+    fn bytes_encode(item: &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
+        Ok(Cow::Borrowed(item.as_bytes()))
     }
 }
diff --git a/meilisearch-auth/src/store.rs b/meilisearch-auth/src/store.rs
index 28ec8b5e4..944082285 100644
--- a/meilisearch-auth/src/store.rs
+++ b/meilisearch-auth/src/store.rs
@@ -4,11 +4,13 @@ use std::collections::HashSet;
 use std::convert::{TryFrom, TryInto};
 use std::fs::create_dir_all;
 use std::path::Path;
+use std::result::Result as StdResult;
 use std::str;
 use std::str::FromStr;
 use std::sync::Arc;
 
 use hmac::{Hmac, Mac};
+use meilisearch_types::heed::BoxedError;
 use meilisearch_types::index_uid_pattern::IndexUidPattern;
 use meilisearch_types::keys::KeyId;
 use meilisearch_types::milli;
@@ -294,23 +296,23 @@ pub struct KeyIdActionCodec;
 impl<'a> milli::heed::BytesDecode<'a> for KeyIdActionCodec {
     type DItem = (KeyId, Action, Option<&'a [u8]>);
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let (key_id_bytes, action_bytes) = try_split_array_at(bytes)?;
-        let (action_bytes, index) = match try_split_array_at(action_bytes)? {
+    fn bytes_decode(bytes: &'a [u8]) -> StdResult<Self::DItem, BoxedError> {
+        let (key_id_bytes, action_bytes) = try_split_array_at(bytes).unwrap();
+        let (action_bytes, index) = match try_split_array_at(action_bytes).unwrap() {
             (action, []) => (action, None),
             (action, index) => (action, Some(index)),
         };
         let key_id = Uuid::from_bytes(*key_id_bytes);
-        let action = Action::from_repr(u8::from_be_bytes(*action_bytes))?;
+        let action = Action::from_repr(u8::from_be_bytes(*action_bytes)).unwrap();
 
-        Some((key_id, action, index))
+        Ok((key_id, action, index))
     }
 }
 
 impl<'a> milli::heed::BytesEncode<'a> for KeyIdActionCodec {
     type EItem = (&'a KeyId, &'a Action, Option<&'a [u8]>);
 
-    fn bytes_encode((key_id, action, index): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((key_id, action, index): &Self::EItem) -> StdResult<Cow<[u8]>, BoxedError> {
         let mut bytes = Vec::new();
 
         bytes.extend_from_slice(key_id.as_bytes());
@@ -320,7 +322,7 @@ impl<'a> milli::heed::BytesEncode<'a> for KeyIdActionCodec {
             bytes.extend_from_slice(index);
         }
 
-        Some(Cow::Owned(bytes))
+        Ok(Cow::Owned(bytes))
     }
 }
 
diff --git a/meilisearch-types/src/error.rs b/meilisearch-types/src/error.rs
index afe9c5189..653cb108b 100644
--- a/meilisearch-types/src/error.rs
+++ b/meilisearch-types/src/error.rs
@@ -386,11 +386,11 @@ impl ErrorCode for HeedError {
             HeedError::Mdb(MdbError::Invalid) => Code::InvalidStoreFile,
             HeedError::Io(e) => e.error_code(),
             HeedError::Mdb(_)
-            | HeedError::Encoding
-            | HeedError::Decoding
+            | HeedError::Encoding(_)
+            | HeedError::Decoding(_)
             | HeedError::InvalidDatabaseTyping
             | HeedError::DatabaseClosing
-            | HeedError::BadOpenOptions => Code::Internal,
+            | HeedError::BadOpenOptions { .. } => Code::Internal,
         }
     }
 }
diff --git a/meilitool/src/main.rs b/meilitool/src/main.rs
index 2b40e42c2..f199df216 100644
--- a/meilitool/src/main.rs
+++ b/meilitool/src/main.rs
@@ -7,8 +7,8 @@ use clap::{Parser, Subcommand};
 use dump::{DumpWriter, IndexMetadata};
 use file_store::FileStore;
 use meilisearch_auth::AuthController;
-use meilisearch_types::heed::types::{OwnedType, SerdeJson, Str};
-use meilisearch_types::heed::{Database, Env, EnvOpenOptions, PolyDatabase, RoTxn, RwTxn};
+use meilisearch_types::heed::types::{SerdeJson, Str};
+use meilisearch_types::heed::{Database, Env, EnvOpenOptions, RoTxn, RwTxn, Unspecified};
 use meilisearch_types::milli::documents::{obkv_to_object, DocumentsBatchReader};
 use meilisearch_types::milli::{obkv_to_json, BEU32};
 use meilisearch_types::tasks::{Status, Task};
@@ -148,15 +148,17 @@ fn try_opening_poly_database(
     env: &Env,
     rtxn: &RoTxn,
     db_name: &str,
-) -> anyhow::Result<PolyDatabase> {
-    env.open_poly_database(rtxn, Some(db_name))
+) -> anyhow::Result<Database<Unspecified, Unspecified>> {
+    env.database_options()
+        .name(db_name)
+        .open(rtxn)
         .with_context(|| format!("While opening the {db_name:?} poly database"))?
         .with_context(|| format!("Missing the {db_name:?} poly database"))
 }
 
 fn try_clearing_poly_database(
     wtxn: &mut RwTxn,
-    database: PolyDatabase,
+    database: Database<Unspecified, Unspecified>,
     db_name: &str,
 ) -> anyhow::Result<()> {
     database.clear(wtxn).with_context(|| format!("While clearing the {db_name:?} database"))
@@ -212,7 +214,7 @@ fn export_a_dump(
     eprintln!("Successfully dumped {count} keys!");
 
     let rtxn = env.read_txn()?;
-    let all_tasks: Database<OwnedType<BEU32>, SerdeJson<Task>> =
+    let all_tasks: Database<BEU32, SerdeJson<Task>> =
         try_opening_database(&env, &rtxn, "all-tasks")?;
     let index_mapping: Database<Str, UuidCodec> =
         try_opening_database(&env, &rtxn, "index-mapping")?;
diff --git a/meilitool/src/uuid_codec.rs b/meilitool/src/uuid_codec.rs
index 70a92ca94..54020fa3c 100644
--- a/meilitool/src/uuid_codec.rs
+++ b/meilitool/src/uuid_codec.rs
@@ -1,7 +1,7 @@
 use std::borrow::Cow;
 use std::convert::TryInto;
 
-use meilisearch_types::heed::{BytesDecode, BytesEncode};
+use meilisearch_types::heed::{BoxedError, BytesDecode, BytesEncode};
 use uuid::Uuid;
 
 /// A heed codec for value of struct Uuid.
@@ -10,15 +10,15 @@ pub struct UuidCodec;
 impl<'a> BytesDecode<'a> for UuidCodec {
     type DItem = Uuid;
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        bytes.try_into().ok().map(Uuid::from_bytes)
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        bytes.try_into().map(Uuid::from_bytes).map_err(Into::into)
     }
 }
 
 impl BytesEncode<'_> for UuidCodec {
     type EItem = Uuid;
 
-    fn bytes_encode(item: &Self::EItem) -> Option<Cow<[u8]>> {
-        Some(Cow::Borrowed(item.as_bytes()))
+    fn bytes_encode(item: &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
+        Ok(Cow::Borrowed(item.as_bytes()))
     }
 }
diff --git a/milli/Cargo.toml b/milli/Cargo.toml
index 190c8e4e2..e563f5d82 100644
--- a/milli/Cargo.toml
+++ b/milli/Cargo.toml
@@ -29,8 +29,8 @@ geoutils = "0.5.1"
 grenad = { version = "0.4.5", default-features = false, features = [
     "rayon", "tempfile"
 ] }
-heed = { git = "https://github.com/meilisearch/heed", branch = "put-current-with-data-codec", default-features = false, features = [
-    "read-txn-no-tls"
+heed = { git = "https://github.com/meilisearch/heed", branch = "main", default-features = false, features = [
+    "serde-json", "serde-bincode", "read-txn-no-tls"
 ] }
 indexmap = { version = "2.0.0", features = ["serde"] }
 instant-distance = { version = "0.6.1", features = ["with-serde"] }
diff --git a/milli/src/error.rs b/milli/src/error.rs
index b249f2977..cbbd8a3e5 100644
--- a/milli/src/error.rs
+++ b/milli/src/error.rs
@@ -152,7 +152,7 @@ only composed of alphanumeric characters (a-z A-Z 0-9), hyphens (-) and undersco
         valid_fields: BTreeSet<String>,
         hidden_fields: bool,
     },
-    #[error("{}", HeedError::BadOpenOptions)]
+    #[error("an environment is already opened with different options")]
     InvalidLmdbOpenOptions,
     #[error("You must specify where `sort` is listed in the rankingRules setting to use the sort parameter at search time.")]
     SortRankingRuleMissing,
@@ -326,11 +326,12 @@ impl From<HeedError> for Error {
             HeedError::Mdb(MdbError::MapFull) => UserError(MaxDatabaseSizeReached),
             HeedError::Mdb(MdbError::Invalid) => UserError(InvalidStoreFile),
             HeedError::Mdb(error) => InternalError(Store(error)),
-            HeedError::Encoding => InternalError(Serialization(Encoding { db_name: None })),
-            HeedError::Decoding => InternalError(Serialization(Decoding { db_name: None })),
+            // TODO use the encoding
+            HeedError::Encoding(_) => InternalError(Serialization(Encoding { db_name: None })),
+            HeedError::Decoding(_) => InternalError(Serialization(Decoding { db_name: None })),
             HeedError::InvalidDatabaseTyping => InternalError(InvalidDatabaseTyping),
             HeedError::DatabaseClosing => InternalError(DatabaseClosing),
-            HeedError::BadOpenOptions => UserError(InvalidLmdbOpenOptions),
+            HeedError::BadOpenOptions { .. } => UserError(InvalidLmdbOpenOptions),
         }
     }
 }
diff --git a/milli/src/external_documents_ids.rs b/milli/src/external_documents_ids.rs
index ec419446c..7e0f795a4 100644
--- a/milli/src/external_documents_ids.rs
+++ b/milli/src/external_documents_ids.rs
@@ -1,6 +1,6 @@
 use std::collections::HashMap;
 
-use heed::types::{OwnedType, Str};
+use heed::types::Str;
 use heed::{Database, RoIter, RoTxn, RwTxn};
 
 use crate::{DocumentId, BEU32};
@@ -16,10 +16,10 @@ pub struct DocumentOperation {
     pub kind: DocumentOperationKind,
 }
 
-pub struct ExternalDocumentsIds(Database<Str, OwnedType<BEU32>>);
+pub struct ExternalDocumentsIds(Database<Str, BEU32>);
 
 impl ExternalDocumentsIds {
-    pub fn new(db: Database<Str, OwnedType<BEU32>>) -> ExternalDocumentsIds {
+    pub fn new(db: Database<Str, BEU32>) -> ExternalDocumentsIds {
         ExternalDocumentsIds(db)
     }
 
@@ -29,7 +29,7 @@ impl ExternalDocumentsIds {
     }
 
     pub fn get<A: AsRef<str>>(&self, rtxn: &RoTxn, external_id: A) -> heed::Result<Option<u32>> {
-        Ok(self.0.get(rtxn, external_id.as_ref())?.map(|x| x.get()))
+        Ok(self.0.get(rtxn, external_id.as_ref())?)
     }
 
     /// An helper function to debug this type, returns an `HashMap` of both,
@@ -38,7 +38,7 @@ impl ExternalDocumentsIds {
         let mut map = HashMap::default();
         for result in self.0.iter(rtxn)? {
             let (external, internal) = result?;
-            map.insert(external.to_owned(), internal.get());
+            map.insert(external.to_owned(), internal);
         }
         Ok(map)
     }
@@ -55,7 +55,7 @@ impl ExternalDocumentsIds {
         for DocumentOperation { external_id, internal_id, kind } in operations {
             match kind {
                 DocumentOperationKind::Create => {
-                    self.0.put(wtxn, &external_id, &BEU32::new(internal_id))?;
+                    self.0.put(wtxn, &external_id, &internal_id)?;
                 }
                 DocumentOperationKind::Delete => {
                     if !self.0.delete(wtxn, &external_id)? {
@@ -69,7 +69,7 @@ impl ExternalDocumentsIds {
     }
 
     /// Returns an iterator over all the external ids.
-    pub fn iter<'t>(&self, rtxn: &'t RoTxn) -> heed::Result<RoIter<'t, Str, OwnedType<BEU32>>> {
+    pub fn iter<'t>(&self, rtxn: &'t RoTxn) -> heed::Result<RoIter<'t, Str, BEU32>> {
         self.0.iter(rtxn)
     }
 }
diff --git a/milli/src/heed_codec/beu16_str_codec.rs b/milli/src/heed_codec/beu16_str_codec.rs
index d1b85d47f..ba04f0900 100644
--- a/milli/src/heed_codec/beu16_str_codec.rs
+++ b/milli/src/heed_codec/beu16_str_codec.rs
@@ -2,26 +2,28 @@ use std::borrow::Cow;
 use std::convert::TryInto;
 use std::str;
 
+use heed::BoxedError;
+
 pub struct BEU16StrCodec;
 
 impl<'a> heed::BytesDecode<'a> for BEU16StrCodec {
     type DItem = (u16, &'a str);
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
         let (n_bytes, str_bytes) = bytes.split_at(2);
-        let n = n_bytes.try_into().map(u16::from_be_bytes).ok()?;
-        let s = str::from_utf8(str_bytes).ok()?;
-        Some((n, s))
+        let n = n_bytes.try_into().map(u16::from_be_bytes)?;
+        let s = str::from_utf8(str_bytes)?;
+        Ok((n, s))
     }
 }
 
 impl<'a> heed::BytesEncode<'a> for BEU16StrCodec {
     type EItem = (u16, &'a str);
 
-    fn bytes_encode((n, s): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((n, s): &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let mut bytes = Vec::with_capacity(s.len() + 2);
         bytes.extend_from_slice(&n.to_be_bytes());
         bytes.extend_from_slice(s.as_bytes());
-        Some(Cow::Owned(bytes))
+        Ok(Cow::Owned(bytes))
     }
 }
diff --git a/milli/src/heed_codec/beu32_str_codec.rs b/milli/src/heed_codec/beu32_str_codec.rs
index c525d6b5b..762e31ca4 100644
--- a/milli/src/heed_codec/beu32_str_codec.rs
+++ b/milli/src/heed_codec/beu32_str_codec.rs
@@ -2,26 +2,28 @@ use std::borrow::Cow;
 use std::convert::TryInto;
 use std::str;
 
+use heed::BoxedError;
+
 pub struct BEU32StrCodec;
 
 impl<'a> heed::BytesDecode<'a> for BEU32StrCodec {
     type DItem = (u32, &'a str);
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
         let (n_bytes, str_bytes) = bytes.split_at(4);
-        let n = n_bytes.try_into().map(u32::from_be_bytes).ok()?;
-        let s = str::from_utf8(str_bytes).ok()?;
-        Some((n, s))
+        let n = n_bytes.try_into().map(u32::from_be_bytes)?;
+        let s = str::from_utf8(str_bytes)?;
+        Ok((n, s))
     }
 }
 
 impl<'a> heed::BytesEncode<'a> for BEU32StrCodec {
     type EItem = (u32, &'a str);
 
-    fn bytes_encode((n, s): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((n, s): &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let mut bytes = Vec::with_capacity(s.len() + 4);
         bytes.extend_from_slice(&n.to_be_bytes());
         bytes.extend_from_slice(s.as_bytes());
-        Some(Cow::Owned(bytes))
+        Ok(Cow::Owned(bytes))
     }
 }
diff --git a/milli/src/heed_codec/byte_slice_ref.rs b/milli/src/heed_codec/byte_slice_ref.rs
index 48eda63c5..b027c7ebc 100644
--- a/milli/src/heed_codec/byte_slice_ref.rs
+++ b/milli/src/heed_codec/byte_slice_ref.rs
@@ -1,6 +1,6 @@
 use std::borrow::Cow;
 
-use heed::{BytesDecode, BytesEncode};
+use heed::{BoxedError, BytesDecode, BytesEncode};
 
 /// A codec for values of type `&[u8]`. Unlike `ByteSlice`, its `EItem` and `DItem` associated
 /// types are equivalent (= `&'a [u8]`) and these values can reside within another structure.
@@ -9,15 +9,15 @@ pub struct ByteSliceRefCodec;
 impl<'a> BytesEncode<'a> for ByteSliceRefCodec {
     type EItem = &'a [u8];
 
-    fn bytes_encode(item: &'a Self::EItem) -> Option<Cow<'a, [u8]>> {
-        Some(Cow::Borrowed(item))
+    fn bytes_encode(item: &'a Self::EItem) -> Result<Cow<'a, [u8]>, BoxedError> {
+        Ok(Cow::Borrowed(item))
     }
 }
 
 impl<'a> BytesDecode<'a> for ByteSliceRefCodec {
     type DItem = &'a [u8];
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        Some(bytes)
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        Ok(bytes)
     }
 }
diff --git a/milli/src/heed_codec/facet/field_doc_id_facet_codec.rs b/milli/src/heed_codec/facet/field_doc_id_facet_codec.rs
index cc9919ad2..a0bea2c42 100644
--- a/milli/src/heed_codec/facet/field_doc_id_facet_codec.rs
+++ b/milli/src/heed_codec/facet/field_doc_id_facet_codec.rs
@@ -1,7 +1,7 @@
 use std::borrow::Cow;
 use std::marker::PhantomData;
 
-use heed::{BytesDecode, BytesEncode};
+use heed::{BoxedError, BytesDecode, BytesEncode};
 
 use crate::{try_split_array_at, DocumentId, FieldId};
 
@@ -13,16 +13,16 @@ where
 {
     type DItem = (FieldId, DocumentId, C::DItem);
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let (field_id_bytes, bytes) = try_split_array_at(bytes)?;
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        let (field_id_bytes, bytes) = try_split_array_at(bytes).unwrap();
         let field_id = u16::from_be_bytes(field_id_bytes);
 
-        let (document_id_bytes, bytes) = try_split_array_at(bytes)?;
+        let (document_id_bytes, bytes) = try_split_array_at(bytes).unwrap();
         let document_id = u32::from_be_bytes(document_id_bytes);
 
         let value = C::bytes_decode(bytes)?;
 
-        Some((field_id, document_id, value))
+        Ok((field_id, document_id, value))
     }
 }
 
@@ -32,13 +32,15 @@ where
 {
     type EItem = (FieldId, DocumentId, C::EItem);
 
-    fn bytes_encode((field_id, document_id, value): &'a Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode(
+        (field_id, document_id, value): &'a Self::EItem,
+    ) -> Result<Cow<[u8]>, BoxedError> {
         let mut bytes = Vec::with_capacity(32);
         bytes.extend_from_slice(&field_id.to_be_bytes()); // 2 bytes
         bytes.extend_from_slice(&document_id.to_be_bytes()); // 4 bytes
         let value_bytes = C::bytes_encode(value)?;
         // variable length, if f64 -> 16 bytes, if string -> large, potentially
         bytes.extend_from_slice(&value_bytes);
-        Some(Cow::Owned(bytes))
+        Ok(Cow::Owned(bytes))
     }
 }
diff --git a/milli/src/heed_codec/facet/mod.rs b/milli/src/heed_codec/facet/mod.rs
index d36ec8434..e5ff1820c 100644
--- a/milli/src/heed_codec/facet/mod.rs
+++ b/milli/src/heed_codec/facet/mod.rs
@@ -5,8 +5,8 @@ use std::borrow::Cow;
 use std::convert::TryFrom;
 use std::marker::PhantomData;
 
-use heed::types::{DecodeIgnore, OwnedType};
-use heed::{BytesDecode, BytesEncode};
+use heed::types::DecodeIgnore;
+use heed::{BoxedError, BytesDecode, BytesEncode};
 use roaring::RoaringBitmap;
 
 pub use self::field_doc_id_facet_codec::FieldDocIdFacetCodec;
@@ -18,7 +18,7 @@ pub type FieldDocIdFacetF64Codec = FieldDocIdFacetCodec<OrderedF64Codec>;
 pub type FieldDocIdFacetStringCodec = FieldDocIdFacetCodec<StrRefCodec>;
 pub type FieldDocIdFacetIgnoreCodec = FieldDocIdFacetCodec<DecodeIgnore>;
 
-pub type FieldIdCodec = OwnedType<BEU16>;
+pub type FieldIdCodec = BEU16;
 
 /// Tries to split a slice in half at the given middle point,
 /// `None` if the slice is too short.
@@ -58,15 +58,15 @@ where
 {
     type EItem = FacetGroupKey<T::EItem>;
 
-    fn bytes_encode(value: &'a Self::EItem) -> Option<Cow<'a, [u8]>> {
+    fn bytes_encode(value: &'a Self::EItem) -> Result<Cow<'a, [u8]>, BoxedError> {
         let mut v = vec![];
         v.extend_from_slice(&value.field_id.to_be_bytes());
         v.extend_from_slice(&[value.level]);
 
-        let bound = T::bytes_encode(&value.left_bound)?;
+        let bound = T::bytes_encode(&value.left_bound).unwrap();
         v.extend_from_slice(&bound);
 
-        Some(Cow::Owned(v))
+        Ok(Cow::Owned(v))
     }
 }
 impl<'a, T> heed::BytesDecode<'a> for FacetGroupKeyCodec<T>
@@ -75,11 +75,11 @@ where
 {
     type DItem = FacetGroupKey<T::DItem>;
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let fid = u16::from_be_bytes(<[u8; 2]>::try_from(&bytes[0..=1]).ok()?);
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        let fid = u16::from_be_bytes(<[u8; 2]>::try_from(&bytes[0..=1])?);
         let level = bytes[2];
         let bound = T::bytes_decode(&bytes[3..])?;
-        Some(FacetGroupKey { field_id: fid, level, left_bound: bound })
+        Ok(FacetGroupKey { field_id: fid, level, left_bound: bound })
     }
 }
 
@@ -87,17 +87,17 @@ pub struct FacetGroupValueCodec;
 impl<'a> heed::BytesEncode<'a> for FacetGroupValueCodec {
     type EItem = FacetGroupValue;
 
-    fn bytes_encode(value: &'a Self::EItem) -> Option<Cow<'a, [u8]>> {
+    fn bytes_encode(value: &'a Self::EItem) -> Result<Cow<'a, [u8]>, BoxedError> {
         let mut v = vec![value.size];
         CboRoaringBitmapCodec::serialize_into(&value.bitmap, &mut v);
-        Some(Cow::Owned(v))
+        Ok(Cow::Owned(v))
     }
 }
 impl<'a> heed::BytesDecode<'a> for FacetGroupValueCodec {
     type DItem = FacetGroupValue;
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
         let size = bytes[0];
-        let bitmap = CboRoaringBitmapCodec::deserialize_from(&bytes[1..]).ok()?;
-        Some(FacetGroupValue { size, bitmap })
+        let bitmap = CboRoaringBitmapCodec::deserialize_from(&bytes[1..])?;
+        Ok(FacetGroupValue { size, bitmap })
     }
 }
diff --git a/milli/src/heed_codec/facet/ordered_f64_codec.rs b/milli/src/heed_codec/facet/ordered_f64_codec.rs
index 5ac9ffcfc..cbefe499f 100644
--- a/milli/src/heed_codec/facet/ordered_f64_codec.rs
+++ b/milli/src/heed_codec/facet/ordered_f64_codec.rs
@@ -1,7 +1,7 @@
 use std::borrow::Cow;
 use std::convert::TryInto;
 
-use heed::BytesDecode;
+use heed::{BoxedError, BytesDecode};
 
 use crate::facet::value_encoding::f64_into_bytes;
 
@@ -10,28 +10,28 @@ pub struct OrderedF64Codec;
 impl<'a> BytesDecode<'a> for OrderedF64Codec {
     type DItem = f64;
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
         if bytes.len() < 16 {
-            return None;
+            panic!() // TODO don't panic
         }
-        let f = bytes[8..].try_into().ok().map(f64::from_be_bytes)?;
-        Some(f)
+        let f = bytes[8..].try_into().ok().map(f64::from_be_bytes).unwrap();
+        Ok(f)
     }
 }
 
 impl heed::BytesEncode<'_> for OrderedF64Codec {
     type EItem = f64;
 
-    fn bytes_encode(f: &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode(f: &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let mut buffer = [0u8; 16];
 
         // write the globally ordered float
-        let bytes = f64_into_bytes(*f)?;
+        let bytes = f64_into_bytes(*f).unwrap();
         buffer[..8].copy_from_slice(&bytes[..]);
         // Then the f64 value just to be able to read it back
         let bytes = f.to_be_bytes();
         buffer[8..16].copy_from_slice(&bytes[..]);
 
-        Some(Cow::Owned(buffer.to_vec()))
+        Ok(Cow::Owned(buffer.to_vec()))
     }
 }
diff --git a/milli/src/heed_codec/field_id_word_count_codec.rs b/milli/src/heed_codec/field_id_word_count_codec.rs
index aca7a80c4..e284a45a2 100644
--- a/milli/src/heed_codec/field_id_word_count_codec.rs
+++ b/milli/src/heed_codec/field_id_word_count_codec.rs
@@ -1,5 +1,7 @@
 use std::borrow::Cow;
 
+use heed::BoxedError;
+
 use crate::{try_split_array_at, FieldId};
 
 pub struct FieldIdWordCountCodec;
@@ -7,21 +9,21 @@ pub struct FieldIdWordCountCodec;
 impl<'a> heed::BytesDecode<'a> for FieldIdWordCountCodec {
     type DItem = (FieldId, u8);
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let (field_id_bytes, bytes) = try_split_array_at(bytes)?;
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        let (field_id_bytes, bytes) = try_split_array_at(bytes).unwrap();
         let field_id = u16::from_be_bytes(field_id_bytes);
-        let ([word_count], _nothing) = try_split_array_at(bytes)?;
-        Some((field_id, word_count))
+        let ([word_count], _nothing) = try_split_array_at(bytes).unwrap();
+        Ok((field_id, word_count))
     }
 }
 
 impl<'a> heed::BytesEncode<'a> for FieldIdWordCountCodec {
     type EItem = (FieldId, u8);
 
-    fn bytes_encode((field_id, word_count): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((field_id, word_count): &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let mut bytes = Vec::with_capacity(2 + 1);
         bytes.extend_from_slice(&field_id.to_be_bytes());
         bytes.push(*word_count);
-        Some(Cow::Owned(bytes))
+        Ok(Cow::Owned(bytes))
     }
 }
diff --git a/milli/src/heed_codec/fst_set_codec.rs b/milli/src/heed_codec/fst_set_codec.rs
index fc79acf29..b402c8ff3 100644
--- a/milli/src/heed_codec/fst_set_codec.rs
+++ b/milli/src/heed_codec/fst_set_codec.rs
@@ -1,7 +1,7 @@
 use std::borrow::Cow;
 
 use fst::Set;
-use heed::{BytesDecode, BytesEncode};
+use heed::{BoxedError, BytesDecode, BytesEncode};
 
 /// A codec for values of type `Set<&[u8]>`.
 pub struct FstSetCodec;
@@ -9,15 +9,15 @@ pub struct FstSetCodec;
 impl<'a> BytesEncode<'a> for FstSetCodec {
     type EItem = Set<Vec<u8>>;
 
-    fn bytes_encode(item: &'a Self::EItem) -> Option<Cow<'a, [u8]>> {
-        Some(Cow::Borrowed(item.as_fst().as_bytes()))
+    fn bytes_encode(item: &'a Self::EItem) -> Result<Cow<'a, [u8]>, BoxedError> {
+        Ok(Cow::Borrowed(item.as_fst().as_bytes()))
     }
 }
 
 impl<'a> BytesDecode<'a> for FstSetCodec {
     type DItem = Set<&'a [u8]>;
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        Set::new(bytes).ok()
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        Set::new(bytes).map_err(Into::into)
     }
 }
diff --git a/milli/src/heed_codec/mod.rs b/milli/src/heed_codec/mod.rs
index d04eaa644..4b2b0fb6f 100644
--- a/milli/src/heed_codec/mod.rs
+++ b/milli/src/heed_codec/mod.rs
@@ -13,6 +13,7 @@ mod str_ref;
 mod str_str_u8_codec;
 
 pub use byte_slice_ref::ByteSliceRefCodec;
+use heed::BoxedError;
 pub use str_ref::StrRefCodec;
 
 pub use self::beu16_str_codec::BEU16StrCodec;
@@ -31,5 +32,5 @@ pub use self::str_str_u8_codec::{U8StrStrCodec, UncheckedU8StrStrCodec};
 pub trait BytesDecodeOwned {
     type DItem;
 
-    fn bytes_decode_owned(bytes: &[u8]) -> Option<Self::DItem>;
+    fn bytes_decode_owned(bytes: &[u8]) -> Result<Self::DItem, BoxedError>;
 }
diff --git a/milli/src/heed_codec/obkv_codec.rs b/milli/src/heed_codec/obkv_codec.rs
index 6dad771a8..d2408c87d 100644
--- a/milli/src/heed_codec/obkv_codec.rs
+++ b/milli/src/heed_codec/obkv_codec.rs
@@ -1,5 +1,6 @@
 use std::borrow::Cow;
 
+use heed::BoxedError;
 use obkv::{KvReaderU16, KvWriterU16};
 
 pub struct ObkvCodec;
@@ -7,15 +8,15 @@ pub struct ObkvCodec;
 impl<'a> heed::BytesDecode<'a> for ObkvCodec {
     type DItem = KvReaderU16<'a>;
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        Some(KvReaderU16::new(bytes))
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        Ok(KvReaderU16::new(bytes))
     }
 }
 
 impl heed::BytesEncode<'_> for ObkvCodec {
     type EItem = KvWriterU16<Vec<u8>>;
 
-    fn bytes_encode(item: &Self::EItem) -> Option<Cow<[u8]>> {
-        item.clone().into_inner().map(Cow::Owned).ok()
+    fn bytes_encode(item: &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
+        item.clone().into_inner().map(Cow::Owned).map_err(Into::into)
     }
 }
diff --git a/milli/src/heed_codec/roaring_bitmap/bo_roaring_bitmap_codec.rs b/milli/src/heed_codec/roaring_bitmap/bo_roaring_bitmap_codec.rs
index 9ad2e9707..c5e7e3e89 100644
--- a/milli/src/heed_codec/roaring_bitmap/bo_roaring_bitmap_codec.rs
+++ b/milli/src/heed_codec/roaring_bitmap/bo_roaring_bitmap_codec.rs
@@ -2,7 +2,7 @@ use std::borrow::Cow;
 use std::convert::TryInto;
 use std::mem::size_of;
 
-use heed::BytesDecode;
+use heed::{BoxedError, BytesDecode};
 use roaring::RoaringBitmap;
 
 use crate::heed_codec::BytesDecodeOwned;
@@ -19,22 +19,22 @@ impl BoRoaringBitmapCodec {
 impl BytesDecode<'_> for BoRoaringBitmapCodec {
     type DItem = RoaringBitmap;
 
-    fn bytes_decode(bytes: &[u8]) -> Option<Self::DItem> {
+    fn bytes_decode(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
         let mut bitmap = RoaringBitmap::new();
 
         for chunk in bytes.chunks(size_of::<u32>()) {
-            let bytes = chunk.try_into().ok()?;
+            let bytes = chunk.try_into()?;
             bitmap.push(u32::from_ne_bytes(bytes));
         }
 
-        Some(bitmap)
+        Ok(bitmap)
     }
 }
 
 impl BytesDecodeOwned for BoRoaringBitmapCodec {
     type DItem = RoaringBitmap;
 
-    fn bytes_decode_owned(bytes: &[u8]) -> Option<Self::DItem> {
+    fn bytes_decode_owned(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
         Self::bytes_decode(bytes)
     }
 }
@@ -42,9 +42,9 @@ impl BytesDecodeOwned for BoRoaringBitmapCodec {
 impl heed::BytesEncode<'_> for BoRoaringBitmapCodec {
     type EItem = RoaringBitmap;
 
-    fn bytes_encode(item: &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode(item: &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let mut out = Vec::new();
         BoRoaringBitmapCodec::serialize_into(item, &mut out);
-        Some(Cow::Owned(out))
+        Ok(Cow::Owned(out))
     }
 }
diff --git a/milli/src/heed_codec/roaring_bitmap/cbo_roaring_bitmap_codec.rs b/milli/src/heed_codec/roaring_bitmap/cbo_roaring_bitmap_codec.rs
index f635e55af..dcab42c0a 100644
--- a/milli/src/heed_codec/roaring_bitmap/cbo_roaring_bitmap_codec.rs
+++ b/milli/src/heed_codec/roaring_bitmap/cbo_roaring_bitmap_codec.rs
@@ -3,6 +3,7 @@ use std::io;
 use std::mem::size_of;
 
 use byteorder::{NativeEndian, ReadBytesExt, WriteBytesExt};
+use heed::BoxedError;
 use roaring::RoaringBitmap;
 
 use crate::heed_codec::BytesDecodeOwned;
@@ -132,26 +133,26 @@ impl CboRoaringBitmapCodec {
 impl heed::BytesDecode<'_> for CboRoaringBitmapCodec {
     type DItem = RoaringBitmap;
 
-    fn bytes_decode(bytes: &[u8]) -> Option<Self::DItem> {
-        Self::deserialize_from(bytes).ok()
+    fn bytes_decode(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
+        Self::deserialize_from(bytes).map_err(Into::into)
     }
 }
 
 impl BytesDecodeOwned for CboRoaringBitmapCodec {
     type DItem = RoaringBitmap;
 
-    fn bytes_decode_owned(bytes: &[u8]) -> Option<Self::DItem> {
-        Self::deserialize_from(bytes).ok()
+    fn bytes_decode_owned(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
+        Self::deserialize_from(bytes).map_err(Into::into)
     }
 }
 
 impl heed::BytesEncode<'_> for CboRoaringBitmapCodec {
     type EItem = RoaringBitmap;
 
-    fn bytes_encode(item: &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode(item: &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let mut vec = Vec::with_capacity(Self::serialized_size(item));
         Self::serialize_into(item, &mut vec);
-        Some(Cow::Owned(vec))
+        Ok(Cow::Owned(vec))
     }
 }
 
diff --git a/milli/src/heed_codec/roaring_bitmap/roaring_bitmap_codec.rs b/milli/src/heed_codec/roaring_bitmap/roaring_bitmap_codec.rs
index f982cc105..aa532ffdd 100644
--- a/milli/src/heed_codec/roaring_bitmap/roaring_bitmap_codec.rs
+++ b/milli/src/heed_codec/roaring_bitmap/roaring_bitmap_codec.rs
@@ -1,5 +1,6 @@
 use std::borrow::Cow;
 
+use heed::BoxedError;
 use roaring::RoaringBitmap;
 
 use crate::heed_codec::BytesDecodeOwned;
@@ -9,25 +10,25 @@ pub struct RoaringBitmapCodec;
 impl heed::BytesDecode<'_> for RoaringBitmapCodec {
     type DItem = RoaringBitmap;
 
-    fn bytes_decode(bytes: &[u8]) -> Option<Self::DItem> {
-        RoaringBitmap::deserialize_unchecked_from(bytes).ok()
+    fn bytes_decode(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
+        RoaringBitmap::deserialize_unchecked_from(bytes).map_err(Into::into)
     }
 }
 
 impl BytesDecodeOwned for RoaringBitmapCodec {
     type DItem = RoaringBitmap;
 
-    fn bytes_decode_owned(bytes: &[u8]) -> Option<Self::DItem> {
-        RoaringBitmap::deserialize_from(bytes).ok()
+    fn bytes_decode_owned(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
+        RoaringBitmap::deserialize_from(bytes).map_err(Into::into)
     }
 }
 
 impl heed::BytesEncode<'_> for RoaringBitmapCodec {
     type EItem = RoaringBitmap;
 
-    fn bytes_encode(item: &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode(item: &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let mut bytes = Vec::with_capacity(item.serialized_size());
-        item.serialize_into(&mut bytes).ok()?;
-        Some(Cow::Owned(bytes))
+        item.serialize_into(&mut bytes)?;
+        Ok(Cow::Owned(bytes))
     }
 }
diff --git a/milli/src/heed_codec/roaring_bitmap_length/bo_roaring_bitmap_len_codec.rs b/milli/src/heed_codec/roaring_bitmap_length/bo_roaring_bitmap_len_codec.rs
index 8fae60df7..cf4997d26 100644
--- a/milli/src/heed_codec/roaring_bitmap_length/bo_roaring_bitmap_len_codec.rs
+++ b/milli/src/heed_codec/roaring_bitmap_length/bo_roaring_bitmap_len_codec.rs
@@ -1,6 +1,6 @@
 use std::mem;
 
-use heed::BytesDecode;
+use heed::{BoxedError, BytesDecode};
 
 use crate::heed_codec::BytesDecodeOwned;
 
@@ -9,15 +9,15 @@ pub struct BoRoaringBitmapLenCodec;
 impl BytesDecode<'_> for BoRoaringBitmapLenCodec {
     type DItem = u64;
 
-    fn bytes_decode(bytes: &[u8]) -> Option<Self::DItem> {
-        Some((bytes.len() / mem::size_of::<u32>()) as u64)
+    fn bytes_decode(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
+        Ok((bytes.len() / mem::size_of::<u32>()) as u64)
     }
 }
 
 impl BytesDecodeOwned for BoRoaringBitmapLenCodec {
     type DItem = u64;
 
-    fn bytes_decode_owned(bytes: &[u8]) -> Option<Self::DItem> {
+    fn bytes_decode_owned(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
         Self::bytes_decode(bytes)
     }
 }
diff --git a/milli/src/heed_codec/roaring_bitmap_length/cbo_roaring_bitmap_len_codec.rs b/milli/src/heed_codec/roaring_bitmap_length/cbo_roaring_bitmap_len_codec.rs
index 5719a538a..c2565c939 100644
--- a/milli/src/heed_codec/roaring_bitmap_length/cbo_roaring_bitmap_len_codec.rs
+++ b/milli/src/heed_codec/roaring_bitmap_length/cbo_roaring_bitmap_len_codec.rs
@@ -1,6 +1,6 @@
 use std::mem;
 
-use heed::BytesDecode;
+use heed::{BoxedError, BytesDecode};
 
 use super::{BoRoaringBitmapLenCodec, RoaringBitmapLenCodec};
 use crate::heed_codec::roaring_bitmap::cbo_roaring_bitmap_codec::THRESHOLD;
@@ -11,7 +11,7 @@ pub struct CboRoaringBitmapLenCodec;
 impl BytesDecode<'_> for CboRoaringBitmapLenCodec {
     type DItem = u64;
 
-    fn bytes_decode(bytes: &[u8]) -> Option<Self::DItem> {
+    fn bytes_decode(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
         if bytes.len() <= THRESHOLD * mem::size_of::<u32>() {
             // If there is threshold or less than threshold integers that can fit into this array
             // of bytes it means that we used the ByteOrder codec serializer.
@@ -27,7 +27,7 @@ impl BytesDecode<'_> for CboRoaringBitmapLenCodec {
 impl BytesDecodeOwned for CboRoaringBitmapLenCodec {
     type DItem = u64;
 
-    fn bytes_decode_owned(bytes: &[u8]) -> Option<Self::DItem> {
+    fn bytes_decode_owned(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
         Self::bytes_decode(bytes)
     }
 }
diff --git a/milli/src/heed_codec/roaring_bitmap_length/roaring_bitmap_len_codec.rs b/milli/src/heed_codec/roaring_bitmap_length/roaring_bitmap_len_codec.rs
index a9b0506ff..578cb31e2 100644
--- a/milli/src/heed_codec/roaring_bitmap_length/roaring_bitmap_len_codec.rs
+++ b/milli/src/heed_codec/roaring_bitmap_length/roaring_bitmap_len_codec.rs
@@ -2,6 +2,7 @@ use std::io::{self, BufRead, Read};
 use std::mem;
 
 use byteorder::{LittleEndian, ReadBytesExt};
+use heed::BoxedError;
 
 use crate::heed_codec::BytesDecodeOwned;
 
@@ -56,16 +57,16 @@ impl RoaringBitmapLenCodec {
 impl heed::BytesDecode<'_> for RoaringBitmapLenCodec {
     type DItem = u64;
 
-    fn bytes_decode(bytes: &[u8]) -> Option<Self::DItem> {
-        RoaringBitmapLenCodec::deserialize_from_slice(bytes).ok()
+    fn bytes_decode(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
+        RoaringBitmapLenCodec::deserialize_from_slice(bytes).map_err(Into::into)
     }
 }
 
 impl BytesDecodeOwned for RoaringBitmapLenCodec {
     type DItem = u64;
 
-    fn bytes_decode_owned(bytes: &[u8]) -> Option<Self::DItem> {
-        RoaringBitmapLenCodec::deserialize_from_slice(bytes).ok()
+    fn bytes_decode_owned(bytes: &[u8]) -> Result<Self::DItem, BoxedError> {
+        RoaringBitmapLenCodec::deserialize_from_slice(bytes).map_err(Into::into)
     }
 }
 
diff --git a/milli/src/heed_codec/script_language_codec.rs b/milli/src/heed_codec/script_language_codec.rs
index 83e8a7241..83f5bf45f 100644
--- a/milli/src/heed_codec/script_language_codec.rs
+++ b/milli/src/heed_codec/script_language_codec.rs
@@ -2,29 +2,30 @@ use std::borrow::Cow;
 use std::str;
 
 use charabia::{Language, Script};
+use heed::BoxedError;
 
 pub struct ScriptLanguageCodec;
 
 impl<'a> heed::BytesDecode<'a> for ScriptLanguageCodec {
     type DItem = (Script, Language);
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let sep = bytes.iter().position(|b| *b == 0)?;
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        let sep = bytes.iter().position(|b| *b == 0).unwrap();
         let (s_bytes, l_bytes) = bytes.split_at(sep);
-        let script = str::from_utf8(s_bytes).ok()?;
+        let script = str::from_utf8(s_bytes)?;
         let script_name = Script::from_name(script);
-        let lan = str::from_utf8(l_bytes).ok()?;
+        let lan = str::from_utf8(l_bytes)?;
         // skip '\0' byte between the two strings.
         let lan_name = Language::from_name(&lan[1..]);
 
-        Some((script_name, lan_name))
+        Ok((script_name, lan_name))
     }
 }
 
 impl<'a> heed::BytesEncode<'a> for ScriptLanguageCodec {
     type EItem = (Script, Language);
 
-    fn bytes_encode((script, lan): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((script, lan): &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let script_name = script.name().as_bytes();
         let lan_name = lan.name().as_bytes();
 
@@ -33,6 +34,6 @@ impl<'a> heed::BytesEncode<'a> for ScriptLanguageCodec {
         bytes.push(0);
         bytes.extend_from_slice(lan_name);
 
-        Some(Cow::Owned(bytes))
+        Ok(Cow::Owned(bytes))
     }
 }
diff --git a/milli/src/heed_codec/str_beu32_codec.rs b/milli/src/heed_codec/str_beu32_codec.rs
index cce849e37..aace89d78 100644
--- a/milli/src/heed_codec/str_beu32_codec.rs
+++ b/milli/src/heed_codec/str_beu32_codec.rs
@@ -3,37 +3,39 @@ use std::convert::TryInto;
 use std::mem::size_of;
 use std::str;
 
+use heed::BoxedError;
+
 pub struct StrBEU32Codec;
 
 impl<'a> heed::BytesDecode<'a> for StrBEU32Codec {
     type DItem = (&'a str, u32);
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
         let footer_len = size_of::<u32>();
 
         if bytes.len() < footer_len {
-            return None;
+            panic!() // TODO Do not panic
         }
 
         let (word, bytes) = bytes.split_at(bytes.len() - footer_len);
-        let word = str::from_utf8(word).ok()?;
-        let pos = bytes.try_into().map(u32::from_be_bytes).ok()?;
+        let word = str::from_utf8(word)?;
+        let pos = bytes.try_into().map(u32::from_be_bytes)?;
 
-        Some((word, pos))
+        Ok((word, pos))
     }
 }
 
 impl<'a> heed::BytesEncode<'a> for StrBEU32Codec {
     type EItem = (&'a str, u32);
 
-    fn bytes_encode((word, pos): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((word, pos): &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let pos = pos.to_be_bytes();
 
         let mut bytes = Vec::with_capacity(word.len() + pos.len());
         bytes.extend_from_slice(word.as_bytes());
         bytes.extend_from_slice(&pos[..]);
 
-        Some(Cow::Owned(bytes))
+        Ok(Cow::Owned(bytes))
     }
 }
 
@@ -42,26 +44,26 @@ pub struct StrBEU16Codec;
 impl<'a> heed::BytesDecode<'a> for StrBEU16Codec {
     type DItem = (&'a str, u16);
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
         let footer_len = size_of::<u16>();
 
         if bytes.len() < footer_len + 1 {
-            return None;
+            panic!() // TODO do not panic
         }
 
         let (word_plus_nul_byte, bytes) = bytes.split_at(bytes.len() - footer_len);
-        let (_, word) = word_plus_nul_byte.split_last()?;
-        let word = str::from_utf8(word).ok()?;
-        let pos = bytes.try_into().map(u16::from_be_bytes).ok()?;
+        let (_, word) = word_plus_nul_byte.split_last().unwrap();
+        let word = str::from_utf8(word).ok().unwrap();
+        let pos = bytes.try_into().map(u16::from_be_bytes).ok().unwrap();
 
-        Some((word, pos))
+        Ok((word, pos))
     }
 }
 
 impl<'a> heed::BytesEncode<'a> for StrBEU16Codec {
     type EItem = (&'a str, u16);
 
-    fn bytes_encode((word, pos): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((word, pos): &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let pos = pos.to_be_bytes();
 
         let mut bytes = Vec::with_capacity(word.len() + 1 + pos.len());
@@ -69,6 +71,6 @@ impl<'a> heed::BytesEncode<'a> for StrBEU16Codec {
         bytes.push(0);
         bytes.extend_from_slice(&pos[..]);
 
-        Some(Cow::Owned(bytes))
+        Ok(Cow::Owned(bytes))
     }
 }
diff --git a/milli/src/heed_codec/str_ref.rs b/milli/src/heed_codec/str_ref.rs
index ced5cc65e..bdf262a46 100644
--- a/milli/src/heed_codec/str_ref.rs
+++ b/milli/src/heed_codec/str_ref.rs
@@ -1,6 +1,6 @@
 use std::borrow::Cow;
 
-use heed::{BytesDecode, BytesEncode};
+use heed::{BoxedError, BytesDecode, BytesEncode};
 
 /// A codec for values of type `&str`. Unlike `Str`, its `EItem` and `DItem` associated
 /// types are equivalent (= `&'a str`) and these values can reside within another structure.
@@ -8,15 +8,14 @@ pub struct StrRefCodec;
 impl<'a> BytesEncode<'a> for StrRefCodec {
     type EItem = &'a str;
 
-    fn bytes_encode(item: &'a &'a str) -> Option<Cow<'a, [u8]>> {
-        Some(Cow::Borrowed(item.as_bytes()))
+    fn bytes_encode(item: &'a &'a str) -> Result<Cow<'a, [u8]>, BoxedError> {
+        Ok(Cow::Borrowed(item.as_bytes()))
     }
 }
 impl<'a> BytesDecode<'a> for StrRefCodec {
     type DItem = &'a str;
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let s = std::str::from_utf8(bytes).ok()?;
-        Some(s)
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        std::str::from_utf8(bytes).map_err(Into::into)
     }
 }
diff --git a/milli/src/heed_codec/str_str_u8_codec.rs b/milli/src/heed_codec/str_str_u8_codec.rs
index 60be8ddc7..c6ba7ebac 100644
--- a/milli/src/heed_codec/str_str_u8_codec.rs
+++ b/milli/src/heed_codec/str_str_u8_codec.rs
@@ -1,32 +1,34 @@
 use std::borrow::Cow;
 use std::str;
 
+use heed::BoxedError;
+
 pub struct U8StrStrCodec;
 
 impl<'a> heed::BytesDecode<'a> for U8StrStrCodec {
     type DItem = (u8, &'a str, &'a str);
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let (n, bytes) = bytes.split_first()?;
-        let s1_end = bytes.iter().position(|b| *b == 0)?;
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        let (n, bytes) = bytes.split_first().unwrap();
+        let s1_end = bytes.iter().position(|b| *b == 0).unwrap();
         let (s1_bytes, rest) = bytes.split_at(s1_end);
         let s2_bytes = &rest[1..];
-        let s1 = str::from_utf8(s1_bytes).ok()?;
-        let s2 = str::from_utf8(s2_bytes).ok()?;
-        Some((*n, s1, s2))
+        let s1 = str::from_utf8(s1_bytes).ok().unwrap();
+        let s2 = str::from_utf8(s2_bytes).ok().unwrap();
+        Ok((*n, s1, s2))
     }
 }
 
 impl<'a> heed::BytesEncode<'a> for U8StrStrCodec {
     type EItem = (u8, &'a str, &'a str);
 
-    fn bytes_encode((n, s1, s2): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((n, s1, s2): &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let mut bytes = Vec::with_capacity(s1.len() + s2.len() + 1);
         bytes.push(*n);
         bytes.extend_from_slice(s1.as_bytes());
         bytes.push(0);
         bytes.extend_from_slice(s2.as_bytes());
-        Some(Cow::Owned(bytes))
+        Ok(Cow::Owned(bytes))
     }
 }
 pub struct UncheckedU8StrStrCodec;
@@ -34,24 +36,24 @@ pub struct UncheckedU8StrStrCodec;
 impl<'a> heed::BytesDecode<'a> for UncheckedU8StrStrCodec {
     type DItem = (u8, &'a [u8], &'a [u8]);
 
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let (n, bytes) = bytes.split_first()?;
-        let s1_end = bytes.iter().position(|b| *b == 0)?;
+    fn bytes_decode(bytes: &'a [u8]) -> Result<Self::DItem, BoxedError> {
+        let (n, bytes) = bytes.split_first().unwrap();
+        let s1_end = bytes.iter().position(|b| *b == 0).unwrap();
         let (s1_bytes, rest) = bytes.split_at(s1_end);
         let s2_bytes = &rest[1..];
-        Some((*n, s1_bytes, s2_bytes))
+        Ok((*n, s1_bytes, s2_bytes))
     }
 }
 
 impl<'a> heed::BytesEncode<'a> for UncheckedU8StrStrCodec {
     type EItem = (u8, &'a [u8], &'a [u8]);
 
-    fn bytes_encode((n, s1, s2): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((n, s1, s2): &Self::EItem) -> Result<Cow<[u8]>, BoxedError> {
         let mut bytes = Vec::with_capacity(s1.len() + s2.len() + 1);
         bytes.push(*n);
         bytes.extend_from_slice(s1);
         bytes.push(0);
         bytes.extend_from_slice(s2);
-        Some(Cow::Owned(bytes))
+        Ok(Cow::Owned(bytes))
     }
 }
diff --git a/milli/src/index.rs b/milli/src/index.rs
index f8cceb0ef..0b57c42ff 100644
--- a/milli/src/index.rs
+++ b/milli/src/index.rs
@@ -4,9 +4,8 @@ use std::fs::File;
 use std::path::Path;
 
 use charabia::{Language, Script};
-use heed::flags::Flags;
 use heed::types::*;
-use heed::{CompactionOption, Database, PolyDatabase, RoTxn, RwTxn};
+use heed::{CompactionOption, Database, RoTxn, RwTxn, Unspecified};
 use roaring::RoaringBitmap;
 use rstar::RTree;
 use time::OffsetDateTime;
@@ -109,10 +108,10 @@ pub struct Index {
     pub(crate) env: heed::Env,
 
     /// Contains many different types (e.g. the fields ids map).
-    pub(crate) main: PolyDatabase,
+    pub(crate) main: Database<Unspecified, Unspecified>,
 
     /// Maps the external documents ids with the internal document id.
-    pub external_documents_ids: Database<Str, OwnedType<BEU32>>,
+    pub external_documents_ids: Database<Str, BEU32>,
 
     /// A word and all the documents ids containing the word.
     pub word_docids: Database<Str, CboRoaringBitmapCodec>,
@@ -158,7 +157,7 @@ pub struct Index {
     /// Maps the facet field id of the normalized-for-search string facets with their original versions.
     pub facet_id_normalized_string_strings: Database<BEU16StrCodec, SerdeJson<BTreeSet<String>>>,
     /// Maps the facet field id of the string facets with an FST containing all the facets values.
-    pub facet_id_string_fst: Database<OwnedType<BEU16>, FstSetCodec>,
+    pub facet_id_string_fst: Database<BEU16, FstSetCodec>,
 
     /// Maps the document id, the facet field id and the numbers.
     pub field_id_docid_facet_f64s: Database<FieldDocIdFacetF64Codec, Unit>,
@@ -166,10 +165,10 @@ pub struct Index {
     pub field_id_docid_facet_strings: Database<FieldDocIdFacetStringCodec, Str>,
 
     /// Maps a vector id to the document id that have it.
-    pub vector_id_docid: Database<OwnedType<BEU32>, OwnedType<BEU32>>,
+    pub vector_id_docid: Database<BEU32, BEU32>,
 
     /// Maps the document id to the document as an obkv store.
-    pub(crate) documents: Database<OwnedType<BEU32>, ObkvCodec>,
+    pub(crate) documents: Database<BEU32, ObkvCodec>,
 }
 
 impl Index {
@@ -182,11 +181,10 @@ impl Index {
         use db_name::*;
 
         options.max_dbs(24);
-        unsafe { options.flag(Flags::MdbAlwaysFreePages) };
 
         let env = options.open(path)?;
         let mut wtxn = env.write_txn()?;
-        let main = env.create_poly_database(&mut wtxn, Some(MAIN))?;
+        let main = env.database_options().name(MAIN).create(&mut wtxn)?;
         let word_docids = env.create_database(&mut wtxn, Some(WORD_DOCIDS))?;
         let external_documents_ids =
             env.create_database(&mut wtxn, Some(EXTERNAL_DOCUMENTS_IDS))?;
@@ -264,20 +262,23 @@ impl Index {
 
     fn set_creation_dates(
         env: &heed::Env,
-        main: PolyDatabase,
+        main: Database<Unspecified, Unspecified>,
         created_at: OffsetDateTime,
         updated_at: OffsetDateTime,
     ) -> heed::Result<()> {
         let mut txn = env.write_txn()?;
         // The db was just created, we update its metadata with the relevant information.
-        if main.get::<_, Str, SerdeJson<OffsetDateTime>>(&txn, main_key::CREATED_AT_KEY)?.is_none()
+        if main
+            .remap_types::<Str, SerdeJson<OffsetDateTime>>()
+            .get(&txn, main_key::CREATED_AT_KEY)?
+            .is_none()
         {
-            main.put::<_, Str, SerdeJson<OffsetDateTime>>(
+            main.remap_types::<Str, SerdeJson<OffsetDateTime>>().put(
                 &mut txn,
                 main_key::UPDATED_AT_KEY,
                 &updated_at,
             )?;
-            main.put::<_, Str, SerdeJson<OffsetDateTime>>(
+            main.remap_types::<Str, SerdeJson<OffsetDateTime>>().put(
                 &mut txn,
                 main_key::CREATED_AT_KEY,
                 &created_at,
@@ -319,11 +320,11 @@ impl Index {
     /// This value is the maximum between the map size passed during the opening of the index
     /// and the on-disk size of the index at the time of opening.
     pub fn map_size(&self) -> Result<usize> {
-        Ok(self.env.map_size()?)
+        Ok(self.env.info().map_size) // TODO remove Result
     }
 
     pub fn copy_to_path<P: AsRef<Path>>(&self, path: P, option: CompactionOption) -> Result<File> {
-        self.env.copy_to_path(path, option).map_err(Into::into)
+        self.env.copy_to_file(path, option).map_err(Into::into)
     }
 
     /// Returns an `EnvClosingEvent` that can be used to wait for the closing event,
@@ -343,21 +344,28 @@ impl Index {
         wtxn: &mut RwTxn,
         docids: &RoaringBitmap,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, RoaringBitmapCodec>(wtxn, main_key::DOCUMENTS_IDS_KEY, docids)
+        self.main.remap_types::<Str, RoaringBitmapCodec>().put(
+            wtxn,
+            main_key::DOCUMENTS_IDS_KEY,
+            docids,
+        )
     }
 
     /// Returns the internal documents ids.
     pub fn documents_ids(&self, rtxn: &RoTxn) -> heed::Result<RoaringBitmap> {
         Ok(self
             .main
-            .get::<_, Str, RoaringBitmapCodec>(rtxn, main_key::DOCUMENTS_IDS_KEY)?
+            .remap_types::<Str, RoaringBitmapCodec>()
+            .get(rtxn, main_key::DOCUMENTS_IDS_KEY)?
             .unwrap_or_default())
     }
 
     /// Returns the number of documents indexed in the database.
     pub fn number_of_documents(&self, rtxn: &RoTxn) -> Result<u64> {
-        let count =
-            self.main.get::<_, Str, RoaringBitmapLenCodec>(rtxn, main_key::DOCUMENTS_IDS_KEY)?;
+        let count = self
+            .main
+            .remap_types::<Str, RoaringBitmapLenCodec>()
+            .get(rtxn, main_key::DOCUMENTS_IDS_KEY)?;
         Ok(count.unwrap_or_default())
     }
 
@@ -366,17 +374,17 @@ impl Index {
     /// Writes the documents primary key, this is the field name that is used to store the id.
     pub(crate) fn put_primary_key(&self, wtxn: &mut RwTxn, primary_key: &str) -> heed::Result<()> {
         self.set_updated_at(wtxn, &OffsetDateTime::now_utc())?;
-        self.main.put::<_, Str, Str>(wtxn, main_key::PRIMARY_KEY_KEY, primary_key)
+        self.main.remap_types::<Str, Str>().put(wtxn, main_key::PRIMARY_KEY_KEY, primary_key)
     }
 
     /// Deletes the primary key of the documents, this can be done to reset indexes settings.
     pub(crate) fn delete_primary_key(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::PRIMARY_KEY_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::PRIMARY_KEY_KEY)
     }
 
     /// Returns the documents primary key, `None` if it hasn't been defined.
     pub fn primary_key<'t>(&self, rtxn: &'t RoTxn) -> heed::Result<Option<&'t str>> {
-        self.main.get::<_, Str, Str>(rtxn, main_key::PRIMARY_KEY_KEY)
+        self.main.remap_types::<Str, Str>().get(rtxn, main_key::PRIMARY_KEY_KEY)
     }
 
     /* external documents ids */
@@ -396,7 +404,11 @@ impl Index {
         wtxn: &mut RwTxn,
         map: &FieldsIdsMap,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeJson<FieldsIdsMap>>(wtxn, main_key::FIELDS_IDS_MAP_KEY, map)
+        self.main.remap_types::<Str, SerdeJson<FieldsIdsMap>>().put(
+            wtxn,
+            main_key::FIELDS_IDS_MAP_KEY,
+            map,
+        )
     }
 
     /// Returns the fields ids map which associate the documents keys with an internal field id
@@ -404,7 +416,8 @@ impl Index {
     pub fn fields_ids_map(&self, rtxn: &RoTxn) -> heed::Result<FieldsIdsMap> {
         Ok(self
             .main
-            .get::<_, Str, SerdeJson<FieldsIdsMap>>(rtxn, main_key::FIELDS_IDS_MAP_KEY)?
+            .remap_types::<Str, SerdeJson<FieldsIdsMap>>()
+            .get(rtxn, main_key::FIELDS_IDS_MAP_KEY)?
             .unwrap_or_default())
     }
 
@@ -416,19 +429,24 @@ impl Index {
         wtxn: &mut RwTxn,
         rtree: &RTree<GeoPoint>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeBincode<RTree<GeoPoint>>>(wtxn, main_key::GEO_RTREE_KEY, rtree)
+        self.main.remap_types::<Str, SerdeBincode<RTree<GeoPoint>>>().put(
+            wtxn,
+            main_key::GEO_RTREE_KEY,
+            rtree,
+        )
     }
 
     /// Delete the `rtree` which associates coordinates to documents ids.
     pub(crate) fn delete_geo_rtree(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::GEO_RTREE_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::GEO_RTREE_KEY)
     }
 
     /// Returns the `rtree` which associates coordinates to documents ids.
     pub fn geo_rtree(&self, rtxn: &RoTxn) -> Result<Option<RTree<GeoPoint>>> {
         match self
             .main
-            .get::<_, Str, SerdeBincode<RTree<GeoPoint>>>(rtxn, main_key::GEO_RTREE_KEY)?
+            .remap_types::<Str, SerdeBincode<RTree<GeoPoint>>>()
+            .get(rtxn, main_key::GEO_RTREE_KEY)?
         {
             Some(rtree) => Ok(Some(rtree)),
             None => Ok(None),
@@ -443,7 +461,7 @@ impl Index {
         wtxn: &mut RwTxn,
         docids: &RoaringBitmap,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, RoaringBitmapCodec>(
+        self.main.remap_types::<Str, RoaringBitmapCodec>().put(
             wtxn,
             main_key::GEO_FACETED_DOCUMENTS_IDS_KEY,
             docids,
@@ -452,14 +470,15 @@ impl Index {
 
     /// Delete the documents ids that are faceted with a _geo field.
     pub(crate) fn delete_geo_faceted_documents_ids(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::GEO_FACETED_DOCUMENTS_IDS_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::GEO_FACETED_DOCUMENTS_IDS_KEY)
     }
 
     /// Retrieve all the documents ids that are faceted with a _geo field.
     pub fn geo_faceted_documents_ids(&self, rtxn: &RoTxn) -> heed::Result<RoaringBitmap> {
         match self
             .main
-            .get::<_, Str, RoaringBitmapCodec>(rtxn, main_key::GEO_FACETED_DOCUMENTS_IDS_KEY)?
+            .remap_types::<Str, RoaringBitmapCodec>()
+            .get(rtxn, main_key::GEO_FACETED_DOCUMENTS_IDS_KEY)?
         {
             Some(docids) => Ok(docids),
             None => Ok(RoaringBitmap::new()),
@@ -474,22 +493,22 @@ impl Index {
         self.delete_vector_hnsw(wtxn)?;
 
         let chunk_size = 1024 * 1024 * (1024 + 512); // 1.5 GiB
-        let bytes = bincode::serialize(hnsw).map_err(|_| heed::Error::Encoding)?;
+        let bytes = bincode::serialize(hnsw).map_err(Into::into).map_err(heed::Error::Encoding)?;
         for (i, chunk) in bytes.chunks(chunk_size).enumerate() {
             let i = i as u32;
             let mut key = main_key::VECTOR_HNSW_KEY_PREFIX.as_bytes().to_vec();
             key.extend_from_slice(&i.to_be_bytes());
-            self.main.put::<_, ByteSlice, ByteSlice>(wtxn, &key, chunk)?;
+            self.main.remap_types::<ByteSlice, ByteSlice>().put(wtxn, &key, chunk)?;
         }
         Ok(())
     }
 
     /// Delete the `hnsw`.
     pub(crate) fn delete_vector_hnsw(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        let mut iter = self.main.prefix_iter_mut::<_, ByteSlice, DecodeIgnore>(
-            wtxn,
-            main_key::VECTOR_HNSW_KEY_PREFIX.as_bytes(),
-        )?;
+        let mut iter = self
+            .main
+            .remap_types::<ByteSlice, DecodeIgnore>()
+            .prefix_iter_mut(wtxn, main_key::VECTOR_HNSW_KEY_PREFIX.as_bytes())?;
         let mut deleted = false;
         while iter.next().transpose()?.is_some() {
             // We do not keep a reference to the key or the value.
@@ -501,8 +520,10 @@ impl Index {
     /// Returns the `hnsw`.
     pub fn vector_hnsw(&self, rtxn: &RoTxn) -> Result<Option<Hnsw>> {
         let mut slices = Vec::new();
-        for result in
-            self.main.prefix_iter::<_, Str, ByteSlice>(rtxn, main_key::VECTOR_HNSW_KEY_PREFIX)?
+        for result in self
+            .main
+            .remap_types::<Str, ByteSlice>()
+            .prefix_iter(rtxn, main_key::VECTOR_HNSW_KEY_PREFIX)?
         {
             let (_, slice) = result?;
             slices.push(slice);
@@ -512,7 +533,11 @@ impl Index {
             Ok(None)
         } else {
             let readable_slices: ReadableSlices<_> = slices.into_iter().collect();
-            Ok(Some(bincode::deserialize_from(readable_slices).map_err(|_| heed::Error::Decoding)?))
+            Ok(Some(
+                bincode::deserialize_from(readable_slices)
+                    .map_err(Into::into)
+                    .map_err(heed::Error::Decoding)?,
+            ))
         }
     }
 
@@ -525,7 +550,7 @@ impl Index {
         wtxn: &mut RwTxn,
         distribution: &FieldDistribution,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeJson<FieldDistribution>>(
+        self.main.remap_types::<Str, SerdeJson<FieldDistribution>>().put(
             wtxn,
             main_key::FIELD_DISTRIBUTION_KEY,
             distribution,
@@ -537,7 +562,8 @@ impl Index {
     pub fn field_distribution(&self, rtxn: &RoTxn) -> heed::Result<FieldDistribution> {
         Ok(self
             .main
-            .get::<_, Str, SerdeJson<FieldDistribution>>(rtxn, main_key::FIELD_DISTRIBUTION_KEY)?
+            .remap_types::<Str, SerdeJson<FieldDistribution>>()
+            .get(rtxn, main_key::FIELD_DISTRIBUTION_KEY)?
             .unwrap_or_default())
     }
 
@@ -550,7 +576,7 @@ impl Index {
         wtxn: &mut RwTxn,
         fields: &[&str],
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeBincode<&[&str]>>(
+        self.main.remap_types::<Str, SerdeBincode<&[&str]>>().put(
             wtxn,
             main_key::DISPLAYED_FIELDS_KEY,
             &fields,
@@ -560,13 +586,15 @@ impl Index {
     /// Deletes the displayed fields ids, this will make the engine to display
     /// all the documents attributes in the order of the `FieldsIdsMap`.
     pub(crate) fn delete_displayed_fields(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::DISPLAYED_FIELDS_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::DISPLAYED_FIELDS_KEY)
     }
 
     /// Returns the displayed fields in the order they were set by the user. If it returns
     /// `None` it means that all the attributes are set as displayed in the order of the `FieldsIdsMap`.
     pub fn displayed_fields<'t>(&self, rtxn: &'t RoTxn) -> heed::Result<Option<Vec<&'t str>>> {
-        self.main.get::<_, Str, SerdeBincode<Vec<&'t str>>>(rtxn, main_key::DISPLAYED_FIELDS_KEY)
+        self.main
+            .remap_types::<Str, SerdeBincode<Vec<&'t str>>>()
+            .get(rtxn, main_key::DISPLAYED_FIELDS_KEY)
     }
 
     /// Identical to `displayed_fields`, but returns the ids instead.
@@ -646,7 +674,7 @@ impl Index {
 
     /// Writes the searchable fields, when this list is specified, only these are indexed.
     fn put_searchable_fields(&self, wtxn: &mut RwTxn, fields: &[&str]) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeBincode<&[&str]>>(
+        self.main.remap_types::<Str, SerdeBincode<&[&str]>>().put(
             wtxn,
             main_key::SEARCHABLE_FIELDS_KEY,
             &fields,
@@ -655,13 +683,15 @@ impl Index {
 
     /// Deletes the searchable fields, when no fields are specified, all fields are indexed.
     fn delete_searchable_fields(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::SEARCHABLE_FIELDS_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::SEARCHABLE_FIELDS_KEY)
     }
 
     /// Returns the searchable fields, those are the fields that are indexed,
     /// if the searchable fields aren't there it means that **all** the fields are indexed.
     pub fn searchable_fields<'t>(&self, rtxn: &'t RoTxn) -> heed::Result<Option<Vec<&'t str>>> {
-        self.main.get::<_, Str, SerdeBincode<Vec<&'t str>>>(rtxn, main_key::SEARCHABLE_FIELDS_KEY)
+        self.main
+            .remap_types::<Str, SerdeBincode<Vec<&'t str>>>()
+            .get(rtxn, main_key::SEARCHABLE_FIELDS_KEY)
     }
 
     /// Identical to `searchable_fields`, but returns the ids instead.
@@ -687,7 +717,7 @@ impl Index {
         wtxn: &mut RwTxn,
         fields: &[&str],
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeBincode<_>>(
+        self.main.remap_types::<Str, SerdeBincode<_>>().put(
             wtxn,
             main_key::USER_DEFINED_SEARCHABLE_FIELDS_KEY,
             &fields,
@@ -699,7 +729,7 @@ impl Index {
         &self,
         wtxn: &mut RwTxn,
     ) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::USER_DEFINED_SEARCHABLE_FIELDS_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::USER_DEFINED_SEARCHABLE_FIELDS_KEY)
     }
 
     /// Returns the user defined searchable fields.
@@ -708,7 +738,8 @@ impl Index {
         rtxn: &'t RoTxn,
     ) -> heed::Result<Option<Vec<&'t str>>> {
         self.main
-            .get::<_, Str, SerdeBincode<Vec<_>>>(rtxn, main_key::USER_DEFINED_SEARCHABLE_FIELDS_KEY)
+            .remap_types::<Str, SerdeBincode<Vec<_>>>()
+            .get(rtxn, main_key::USER_DEFINED_SEARCHABLE_FIELDS_KEY)
     }
 
     /* filterable fields */
@@ -719,19 +750,24 @@ impl Index {
         wtxn: &mut RwTxn,
         fields: &HashSet<String>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeJson<_>>(wtxn, main_key::FILTERABLE_FIELDS_KEY, fields)
+        self.main.remap_types::<Str, SerdeJson<_>>().put(
+            wtxn,
+            main_key::FILTERABLE_FIELDS_KEY,
+            fields,
+        )
     }
 
     /// Deletes the filterable fields ids in the database.
     pub(crate) fn delete_filterable_fields(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::FILTERABLE_FIELDS_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::FILTERABLE_FIELDS_KEY)
     }
 
     /// Returns the filterable fields names.
     pub fn filterable_fields(&self, rtxn: &RoTxn) -> heed::Result<HashSet<String>> {
         Ok(self
             .main
-            .get::<_, Str, SerdeJson<_>>(rtxn, main_key::FILTERABLE_FIELDS_KEY)?
+            .remap_types::<Str, SerdeJson<_>>()
+            .get(rtxn, main_key::FILTERABLE_FIELDS_KEY)?
             .unwrap_or_default())
     }
 
@@ -758,19 +794,24 @@ impl Index {
         wtxn: &mut RwTxn,
         fields: &HashSet<String>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeJson<_>>(wtxn, main_key::SORTABLE_FIELDS_KEY, fields)
+        self.main.remap_types::<Str, SerdeJson<_>>().put(
+            wtxn,
+            main_key::SORTABLE_FIELDS_KEY,
+            fields,
+        )
     }
 
     /// Deletes the sortable fields ids in the database.
     pub(crate) fn delete_sortable_fields(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::SORTABLE_FIELDS_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::SORTABLE_FIELDS_KEY)
     }
 
     /// Returns the sortable fields names.
     pub fn sortable_fields(&self, rtxn: &RoTxn) -> heed::Result<HashSet<String>> {
         Ok(self
             .main
-            .get::<_, Str, SerdeJson<_>>(rtxn, main_key::SORTABLE_FIELDS_KEY)?
+            .remap_types::<Str, SerdeJson<_>>()
+            .get(rtxn, main_key::SORTABLE_FIELDS_KEY)?
             .unwrap_or_default())
     }
 
@@ -789,14 +830,19 @@ impl Index {
         wtxn: &mut RwTxn,
         fields: &HashSet<String>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeJson<_>>(wtxn, main_key::HIDDEN_FACETED_FIELDS_KEY, fields)
+        self.main.remap_types::<Str, SerdeJson<_>>().put(
+            wtxn,
+            main_key::HIDDEN_FACETED_FIELDS_KEY,
+            fields,
+        )
     }
 
     /// Returns the faceted fields names.
     pub fn faceted_fields(&self, rtxn: &RoTxn) -> heed::Result<HashSet<String>> {
         Ok(self
             .main
-            .get::<_, Str, SerdeJson<_>>(rtxn, main_key::HIDDEN_FACETED_FIELDS_KEY)?
+            .remap_types::<Str, SerdeJson<_>>()
+            .get(rtxn, main_key::HIDDEN_FACETED_FIELDS_KEY)?
             .unwrap_or_default())
     }
 
@@ -863,7 +909,7 @@ impl Index {
         rtxn: &RoTxn,
         field_id: FieldId,
     ) -> heed::Result<RoaringBitmap> {
-        match self.facet_id_is_null_docids.get(rtxn, &BEU16::new(field_id))? {
+        match self.facet_id_is_null_docids.get(rtxn, &field_id)? {
             Some(docids) => Ok(docids),
             None => Ok(RoaringBitmap::new()),
         }
@@ -875,7 +921,7 @@ impl Index {
         rtxn: &RoTxn,
         field_id: FieldId,
     ) -> heed::Result<RoaringBitmap> {
-        match self.facet_id_is_empty_docids.get(rtxn, &BEU16::new(field_id))? {
+        match self.facet_id_is_empty_docids.get(rtxn, &field_id)? {
             Some(docids) => Ok(docids),
             None => Ok(RoaringBitmap::new()),
         }
@@ -887,7 +933,7 @@ impl Index {
         rtxn: &RoTxn,
         field_id: FieldId,
     ) -> heed::Result<RoaringBitmap> {
-        match self.facet_id_exists_docids.get(rtxn, &BEU16::new(field_id))? {
+        match self.facet_id_exists_docids.get(rtxn, &field_id)? {
             Some(docids) => Ok(docids),
             None => Ok(RoaringBitmap::new()),
         }
@@ -900,15 +946,15 @@ impl Index {
         wtxn: &mut RwTxn,
         distinct_field: &str,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, Str>(wtxn, main_key::DISTINCT_FIELD_KEY, distinct_field)
+        self.main.remap_types::<Str, Str>().put(wtxn, main_key::DISTINCT_FIELD_KEY, distinct_field)
     }
 
     pub fn distinct_field<'a>(&self, rtxn: &'a RoTxn) -> heed::Result<Option<&'a str>> {
-        self.main.get::<_, Str, Str>(rtxn, main_key::DISTINCT_FIELD_KEY)
+        self.main.remap_types::<Str, Str>().get(rtxn, main_key::DISTINCT_FIELD_KEY)
     }
 
     pub(crate) fn delete_distinct_field(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::DISTINCT_FIELD_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::DISTINCT_FIELD_KEY)
     }
 
     /* criteria */
@@ -918,15 +964,23 @@ impl Index {
         wtxn: &mut RwTxn,
         criteria: &[Criterion],
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeJson<&[Criterion]>>(wtxn, main_key::CRITERIA_KEY, &criteria)
+        self.main.remap_types::<Str, SerdeJson<&[Criterion]>>().put(
+            wtxn,
+            main_key::CRITERIA_KEY,
+            &criteria,
+        )
     }
 
     pub(crate) fn delete_criteria(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::CRITERIA_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::CRITERIA_KEY)
     }
 
     pub fn criteria(&self, rtxn: &RoTxn) -> heed::Result<Vec<Criterion>> {
-        match self.main.get::<_, Str, SerdeJson<Vec<Criterion>>>(rtxn, main_key::CRITERIA_KEY)? {
+        match self
+            .main
+            .remap_types::<Str, SerdeJson<Vec<Criterion>>>()
+            .get(rtxn, main_key::CRITERIA_KEY)?
+        {
             Some(criteria) => Ok(criteria),
             None => Ok(default_criteria()),
         }
@@ -940,12 +994,16 @@ impl Index {
         wtxn: &mut RwTxn,
         fst: &fst::Set<A>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, ByteSlice>(wtxn, main_key::WORDS_FST_KEY, fst.as_fst().as_bytes())
+        self.main.remap_types::<Str, ByteSlice>().put(
+            wtxn,
+            main_key::WORDS_FST_KEY,
+            fst.as_fst().as_bytes(),
+        )
     }
 
     /// Returns the FST which is the words dictionary of the engine.
     pub fn words_fst<'t>(&self, rtxn: &'t RoTxn) -> Result<fst::Set<Cow<'t, [u8]>>> {
-        match self.main.get::<_, Str, ByteSlice>(rtxn, main_key::WORDS_FST_KEY)? {
+        match self.main.remap_types::<Str, ByteSlice>().get(rtxn, main_key::WORDS_FST_KEY)? {
             Some(bytes) => Ok(fst::Set::new(bytes)?.map_data(Cow::Borrowed)?),
             None => Ok(fst::Set::default().map_data(Cow::Owned)?),
         }
@@ -958,15 +1016,19 @@ impl Index {
         wtxn: &mut RwTxn,
         fst: &fst::Set<A>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, ByteSlice>(wtxn, main_key::STOP_WORDS_KEY, fst.as_fst().as_bytes())
+        self.main.remap_types::<Str, ByteSlice>().put(
+            wtxn,
+            main_key::STOP_WORDS_KEY,
+            fst.as_fst().as_bytes(),
+        )
     }
 
     pub(crate) fn delete_stop_words(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::STOP_WORDS_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::STOP_WORDS_KEY)
     }
 
     pub fn stop_words<'t>(&self, rtxn: &'t RoTxn) -> Result<Option<fst::Set<&'t [u8]>>> {
-        match self.main.get::<_, Str, ByteSlice>(rtxn, main_key::STOP_WORDS_KEY)? {
+        match self.main.remap_types::<Str, ByteSlice>().get(rtxn, main_key::STOP_WORDS_KEY)? {
             Some(bytes) => Ok(Some(fst::Set::new(bytes)?)),
             None => Ok(None),
         }
@@ -979,18 +1041,22 @@ impl Index {
         wtxn: &mut RwTxn,
         set: &BTreeSet<String>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeBincode<_>>(wtxn, main_key::NON_SEPARATOR_TOKENS_KEY, set)
+        self.main.remap_types::<Str, SerdeBincode<_>>().put(
+            wtxn,
+            main_key::NON_SEPARATOR_TOKENS_KEY,
+            set,
+        )
     }
 
     pub(crate) fn delete_non_separator_tokens(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::NON_SEPARATOR_TOKENS_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::NON_SEPARATOR_TOKENS_KEY)
     }
 
     pub fn non_separator_tokens(&self, rtxn: &RoTxn) -> Result<Option<BTreeSet<String>>> {
-        Ok(self.main.get::<_, Str, SerdeBincode<BTreeSet<String>>>(
-            rtxn,
-            main_key::NON_SEPARATOR_TOKENS_KEY,
-        )?)
+        Ok(self
+            .main
+            .remap_types::<Str, SerdeBincode<BTreeSet<String>>>()
+            .get(rtxn, main_key::NON_SEPARATOR_TOKENS_KEY)?)
     }
 
     /* separator tokens */
@@ -1000,17 +1066,22 @@ impl Index {
         wtxn: &mut RwTxn,
         set: &BTreeSet<String>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeBincode<_>>(wtxn, main_key::SEPARATOR_TOKENS_KEY, set)
+        self.main.remap_types::<Str, SerdeBincode<_>>().put(
+            wtxn,
+            main_key::SEPARATOR_TOKENS_KEY,
+            set,
+        )
     }
 
     pub(crate) fn delete_separator_tokens(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::SEPARATOR_TOKENS_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::SEPARATOR_TOKENS_KEY)
     }
 
     pub fn separator_tokens(&self, rtxn: &RoTxn) -> Result<Option<BTreeSet<String>>> {
         Ok(self
             .main
-            .get::<_, Str, SerdeBincode<BTreeSet<String>>>(rtxn, main_key::SEPARATOR_TOKENS_KEY)?)
+            .remap_types::<Str, SerdeBincode<BTreeSet<String>>>()
+            .get(rtxn, main_key::SEPARATOR_TOKENS_KEY)?)
     }
 
     /* separators easing method */
@@ -1040,17 +1111,18 @@ impl Index {
         wtxn: &mut RwTxn,
         set: &BTreeSet<String>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeBincode<_>>(wtxn, main_key::DICTIONARY_KEY, set)
+        self.main.remap_types::<Str, SerdeBincode<_>>().put(wtxn, main_key::DICTIONARY_KEY, set)
     }
 
     pub(crate) fn delete_dictionary(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::DICTIONARY_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::DICTIONARY_KEY)
     }
 
     pub fn dictionary(&self, rtxn: &RoTxn) -> Result<Option<BTreeSet<String>>> {
         Ok(self
             .main
-            .get::<_, Str, SerdeBincode<BTreeSet<String>>>(rtxn, main_key::DICTIONARY_KEY)?)
+            .remap_types::<Str, SerdeBincode<BTreeSet<String>>>()
+            .get(rtxn, main_key::DICTIONARY_KEY)?)
     }
 
     /* synonyms */
@@ -1061,8 +1133,12 @@ impl Index {
         synonyms: &HashMap<Vec<String>, Vec<Vec<String>>>,
         user_defined_synonyms: &BTreeMap<String, Vec<String>>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeBincode<_>>(wtxn, main_key::SYNONYMS_KEY, synonyms)?;
-        self.main.put::<_, Str, SerdeBincode<_>>(
+        self.main.remap_types::<Str, SerdeBincode<_>>().put(
+            wtxn,
+            main_key::SYNONYMS_KEY,
+            synonyms,
+        )?;
+        self.main.remap_types::<Str, SerdeBincode<_>>().put(
             wtxn,
             main_key::USER_DEFINED_SYNONYMS_KEY,
             user_defined_synonyms,
@@ -1070,8 +1146,8 @@ impl Index {
     }
 
     pub(crate) fn delete_synonyms(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(wtxn, main_key::SYNONYMS_KEY)?;
-        self.main.delete::<_, Str>(wtxn, main_key::USER_DEFINED_SYNONYMS_KEY)
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::SYNONYMS_KEY)?;
+        self.main.remap_key_type::<Str>().delete(wtxn, main_key::USER_DEFINED_SYNONYMS_KEY)
     }
 
     pub fn user_defined_synonyms(
@@ -1080,14 +1156,16 @@ impl Index {
     ) -> heed::Result<BTreeMap<String, Vec<String>>> {
         Ok(self
             .main
-            .get::<_, Str, SerdeBincode<_>>(rtxn, main_key::USER_DEFINED_SYNONYMS_KEY)?
+            .remap_types::<Str, SerdeBincode<_>>()
+            .get(rtxn, main_key::USER_DEFINED_SYNONYMS_KEY)?
             .unwrap_or_default())
     }
 
     pub fn synonyms(&self, rtxn: &RoTxn) -> heed::Result<HashMap<Vec<String>, Vec<Vec<String>>>> {
         Ok(self
             .main
-            .get::<_, Str, SerdeBincode<_>>(rtxn, main_key::SYNONYMS_KEY)?
+            .remap_types::<Str, SerdeBincode<_>>()
+            .get(rtxn, main_key::SYNONYMS_KEY)?
             .unwrap_or_default())
     }
 
@@ -1108,7 +1186,7 @@ impl Index {
         wtxn: &mut RwTxn,
         fst: &fst::Set<A>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, ByteSlice>(
+        self.main.remap_types::<Str, ByteSlice>().put(
             wtxn,
             main_key::WORDS_PREFIXES_FST_KEY,
             fst.as_fst().as_bytes(),
@@ -1117,7 +1195,11 @@ impl Index {
 
     /// Returns the FST which is the words prefixes dictionnary of the engine.
     pub fn words_prefixes_fst<'t>(&self, rtxn: &'t RoTxn) -> Result<fst::Set<Cow<'t, [u8]>>> {
-        match self.main.get::<_, Str, ByteSlice>(rtxn, main_key::WORDS_PREFIXES_FST_KEY)? {
+        match self
+            .main
+            .remap_types::<Str, ByteSlice>()
+            .get(rtxn, main_key::WORDS_PREFIXES_FST_KEY)?
+        {
             Some(bytes) => Ok(fst::Set::new(bytes)?.map_data(Cow::Borrowed)?),
             None => Ok(fst::Set::default().map_data(Cow::Owned)?),
         }
@@ -1142,7 +1224,7 @@ impl Index {
         Ok(ids.into_iter().map(move |id| {
             let kv = self
                 .documents
-                .get(rtxn, &BEU32::new(id))?
+                .get(rtxn, &id)?
                 .ok_or(UserError::UnknownInternalDocumentId { document_id: id })?;
             Ok((id, kv))
         }))
@@ -1207,7 +1289,8 @@ impl Index {
     pub fn created_at(&self, rtxn: &RoTxn) -> Result<OffsetDateTime> {
         Ok(self
             .main
-            .get::<_, Str, SerdeJson<OffsetDateTime>>(rtxn, main_key::CREATED_AT_KEY)?
+            .remap_types::<Str, SerdeJson<OffsetDateTime>>()
+            .get(rtxn, main_key::CREATED_AT_KEY)?
             .ok_or(InternalError::DatabaseMissingEntry {
                 db_name: db_name::MAIN,
                 key: Some(main_key::CREATED_AT_KEY),
@@ -1218,7 +1301,8 @@ impl Index {
     pub fn updated_at(&self, rtxn: &RoTxn) -> Result<OffsetDateTime> {
         Ok(self
             .main
-            .get::<_, Str, SerdeJson<OffsetDateTime>>(rtxn, main_key::UPDATED_AT_KEY)?
+            .remap_types::<Str, SerdeJson<OffsetDateTime>>()
+            .get(rtxn, main_key::UPDATED_AT_KEY)?
             .ok_or(InternalError::DatabaseMissingEntry {
                 db_name: db_name::MAIN,
                 key: Some(main_key::UPDATED_AT_KEY),
@@ -1230,14 +1314,18 @@ impl Index {
         wtxn: &mut RwTxn,
         time: &OffsetDateTime,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeJson<OffsetDateTime>>(wtxn, main_key::UPDATED_AT_KEY, time)
+        self.main.remap_types::<Str, SerdeJson<OffsetDateTime>>().put(
+            wtxn,
+            main_key::UPDATED_AT_KEY,
+            time,
+        )
     }
 
     pub fn authorize_typos(&self, txn: &RoTxn) -> heed::Result<bool> {
         // It is not possible to put a bool in heed with OwnedType, so we put a u8 instead. We
         // identify 0 as being false, and anything else as true. The absence of a value is true,
         // because by default, we authorize typos.
-        match self.main.get::<_, Str, OwnedType<u8>>(txn, main_key::AUTHORIZE_TYPOS)? {
+        match self.main.remap_types::<Str, OwnedType<u8>>().get(txn, main_key::AUTHORIZE_TYPOS)? {
             Some(0) => Ok(false),
             _ => Ok(true),
         }
@@ -1247,7 +1335,11 @@ impl Index {
         // It is not possible to put a bool in heed with OwnedType, so we put a u8 instead. We
         // identify 0 as being false, and anything else as true. The absence of a value is true,
         // because by default, we authorize typos.
-        self.main.put::<_, Str, OwnedType<u8>>(txn, main_key::AUTHORIZE_TYPOS, &(flag as u8))?;
+        self.main.remap_types::<Str, OwnedType<u8>>().put(
+            txn,
+            main_key::AUTHORIZE_TYPOS,
+            &(flag as u8),
+        )?;
 
         Ok(())
     }
@@ -1258,7 +1350,8 @@ impl Index {
         // because by default, we authorize typos.
         Ok(self
             .main
-            .get::<_, Str, OwnedType<u8>>(txn, main_key::ONE_TYPO_WORD_LEN)?
+            .remap_types::<Str, OwnedType<u8>>()
+            .get(txn, main_key::ONE_TYPO_WORD_LEN)?
             .unwrap_or(DEFAULT_MIN_WORD_LEN_ONE_TYPO))
     }
 
@@ -1266,7 +1359,11 @@ impl Index {
         // It is not possible to put a bool in heed with OwnedType, so we put a u8 instead. We
         // identify 0 as being false, and anything else as true. The absence of a value is true,
         // because by default, we authorize typos.
-        self.main.put::<_, Str, OwnedType<u8>>(txn, main_key::ONE_TYPO_WORD_LEN, &val)?;
+        self.main.remap_types::<Str, OwnedType<u8>>().put(
+            txn,
+            main_key::ONE_TYPO_WORD_LEN,
+            &val,
+        )?;
         Ok(())
     }
 
@@ -1276,7 +1373,8 @@ impl Index {
         // because by default, we authorize typos.
         Ok(self
             .main
-            .get::<_, Str, OwnedType<u8>>(txn, main_key::TWO_TYPOS_WORD_LEN)?
+            .remap_types::<Str, OwnedType<u8>>()
+            .get(txn, main_key::TWO_TYPOS_WORD_LEN)?
             .unwrap_or(DEFAULT_MIN_WORD_LEN_TWO_TYPOS))
     }
 
@@ -1284,13 +1382,17 @@ impl Index {
         // It is not possible to put a bool in heed with OwnedType, so we put a u8 instead. We
         // identify 0 as being false, and anything else as true. The absence of a value is true,
         // because by default, we authorize typos.
-        self.main.put::<_, Str, OwnedType<u8>>(txn, main_key::TWO_TYPOS_WORD_LEN, &val)?;
+        self.main.remap_types::<Str, OwnedType<u8>>().put(
+            txn,
+            main_key::TWO_TYPOS_WORD_LEN,
+            &val,
+        )?;
         Ok(())
     }
 
     /// List the words on which typo are not allowed
     pub fn exact_words<'t>(&self, txn: &'t RoTxn) -> Result<Option<fst::Set<Cow<'t, [u8]>>>> {
-        match self.main.get::<_, Str, ByteSlice>(txn, main_key::EXACT_WORDS)? {
+        match self.main.remap_types::<Str, ByteSlice>().get(txn, main_key::EXACT_WORDS)? {
             Some(bytes) => Ok(Some(fst::Set::new(bytes)?.map_data(Cow::Borrowed)?)),
             None => Ok(None),
         }
@@ -1301,7 +1403,7 @@ impl Index {
         txn: &mut RwTxn,
         words: &fst::Set<A>,
     ) -> Result<()> {
-        self.main.put::<_, Str, ByteSlice>(
+        self.main.remap_types::<Str, ByteSlice>().put(
             txn,
             main_key::EXACT_WORDS,
             words.as_fst().as_bytes(),
@@ -1313,7 +1415,8 @@ impl Index {
     pub fn exact_attributes<'t>(&self, txn: &'t RoTxn) -> Result<Vec<&'t str>> {
         Ok(self
             .main
-            .get::<_, Str, SerdeBincode<Vec<&str>>>(txn, main_key::EXACT_ATTRIBUTES)?
+            .remap_types::<Str, SerdeBincode<Vec<&str>>>()
+            .get(txn, main_key::EXACT_ATTRIBUTES)?
             .unwrap_or_default())
     }
 
@@ -1326,34 +1429,40 @@ impl Index {
 
     /// Writes the exact attributes to the database.
     pub(crate) fn put_exact_attributes(&self, txn: &mut RwTxn, attrs: &[&str]) -> Result<()> {
-        self.main.put::<_, Str, SerdeBincode<&[&str]>>(txn, main_key::EXACT_ATTRIBUTES, &attrs)?;
+        self.main.remap_types::<Str, SerdeBincode<&[&str]>>().put(
+            txn,
+            main_key::EXACT_ATTRIBUTES,
+            &attrs,
+        )?;
         Ok(())
     }
 
     /// Clears the exact attributes from the store.
     pub(crate) fn delete_exact_attributes(&self, txn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(txn, main_key::EXACT_ATTRIBUTES)
+        self.main.remap_key_type::<Str>().delete(txn, main_key::EXACT_ATTRIBUTES)
     }
 
     pub fn max_values_per_facet(&self, txn: &RoTxn) -> heed::Result<Option<usize>> {
-        self.main.get::<_, Str, OwnedType<usize>>(txn, main_key::MAX_VALUES_PER_FACET)
+        self.main.remap_types::<Str, OwnedType<usize>>().get(txn, main_key::MAX_VALUES_PER_FACET)
     }
 
     pub(crate) fn put_max_values_per_facet(&self, txn: &mut RwTxn, val: usize) -> heed::Result<()> {
-        self.main.put::<_, Str, OwnedType<usize>>(txn, main_key::MAX_VALUES_PER_FACET, &val)
+        self.main.remap_types::<Str, OwnedType<usize>>().put(
+            txn,
+            main_key::MAX_VALUES_PER_FACET,
+            &val,
+        )
     }
 
     pub(crate) fn delete_max_values_per_facet(&self, txn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(txn, main_key::MAX_VALUES_PER_FACET)
+        self.main.remap_key_type::<Str>().delete(txn, main_key::MAX_VALUES_PER_FACET)
     }
 
     pub fn sort_facet_values_by(&self, txn: &RoTxn) -> heed::Result<HashMap<String, OrderBy>> {
         let mut orders = self
             .main
-            .get::<_, Str, SerdeJson<HashMap<String, OrderBy>>>(
-                txn,
-                main_key::SORT_FACET_VALUES_BY,
-            )?
+            .remap_types::<Str, SerdeJson<HashMap<String, OrderBy>>>()
+            .get(txn, main_key::SORT_FACET_VALUES_BY)?
             .unwrap_or_default();
         // Insert the default ordering if it is not already overwritten by the user.
         orders.entry("*".to_string()).or_insert(OrderBy::Lexicographic);
@@ -1365,15 +1474,17 @@ impl Index {
         txn: &mut RwTxn,
         val: &HashMap<String, OrderBy>,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, SerdeJson<_>>(txn, main_key::SORT_FACET_VALUES_BY, &val)
+        self.main.remap_types::<Str, SerdeJson<_>>().put(txn, main_key::SORT_FACET_VALUES_BY, &val)
     }
 
     pub(crate) fn delete_sort_facet_values_by(&self, txn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(txn, main_key::SORT_FACET_VALUES_BY)
+        self.main.remap_key_type::<Str>().delete(txn, main_key::SORT_FACET_VALUES_BY)
     }
 
     pub fn pagination_max_total_hits(&self, txn: &RoTxn) -> heed::Result<Option<usize>> {
-        self.main.get::<_, Str, OwnedType<usize>>(txn, main_key::PAGINATION_MAX_TOTAL_HITS)
+        self.main
+            .remap_types::<Str, OwnedType<usize>>()
+            .get(txn, main_key::PAGINATION_MAX_TOTAL_HITS)
     }
 
     pub(crate) fn put_pagination_max_total_hits(
@@ -1381,11 +1492,15 @@ impl Index {
         txn: &mut RwTxn,
         val: usize,
     ) -> heed::Result<()> {
-        self.main.put::<_, Str, OwnedType<usize>>(txn, main_key::PAGINATION_MAX_TOTAL_HITS, &val)
+        self.main.remap_types::<Str, OwnedType<usize>>().put(
+            txn,
+            main_key::PAGINATION_MAX_TOTAL_HITS,
+            &val,
+        )
     }
 
     pub(crate) fn delete_pagination_max_total_hits(&self, txn: &mut RwTxn) -> heed::Result<bool> {
-        self.main.delete::<_, Str>(txn, main_key::PAGINATION_MAX_TOTAL_HITS)
+        self.main.remap_key_type::<Str>().delete(txn, main_key::PAGINATION_MAX_TOTAL_HITS)
     }
 
     /* script  language docids */
diff --git a/milli/src/lib.rs b/milli/src/lib.rs
index cfa438609..acea72c41 100644
--- a/milli/src/lib.rs
+++ b/milli/src/lib.rs
@@ -66,9 +66,9 @@ pub use self::search::{
 pub type Result<T> = std::result::Result<T, error::Error>;
 
 pub type Attribute = u32;
-pub type BEU16 = heed::zerocopy::U16<heed::byteorder::BE>;
-pub type BEU32 = heed::zerocopy::U32<heed::byteorder::BE>;
-pub type BEU64 = heed::zerocopy::U64<heed::byteorder::BE>;
+pub type BEU16 = heed::types::U16<heed::byteorder::BE>;
+pub type BEU32 = heed::types::U32<heed::byteorder::BE>;
+pub type BEU64 = heed::types::U64<heed::byteorder::BE>;
 pub type DocumentId = u32;
 pub type FastMap4<K, V> = HashMap<K, V, BuildHasherDefault<FxHasher32>>;
 pub type FastMap8<K, V> = HashMap<K, V, BuildHasherDefault<FxHasher64>>;
diff --git a/milli/src/search/facet/facet_range_search.rs b/milli/src/search/facet/facet_range_search.rs
index 26854bc1a..f90c331d7 100644
--- a/milli/src/search/facet/facet_range_search.rs
+++ b/milli/src/search/facet/facet_range_search.rs
@@ -25,11 +25,11 @@ where
     let inner;
     let left = match left {
         Bound::Included(left) => {
-            inner = BoundCodec::bytes_encode(left).ok_or(heed::Error::Encoding)?;
+            inner = BoundCodec::bytes_encode(left).map_err(heed::Error::Encoding)?;
             Bound::Included(inner.as_ref())
         }
         Bound::Excluded(left) => {
-            inner = BoundCodec::bytes_encode(left).ok_or(heed::Error::Encoding)?;
+            inner = BoundCodec::bytes_encode(left).map_err(heed::Error::Encoding)?;
             Bound::Excluded(inner.as_ref())
         }
         Bound::Unbounded => Bound::Unbounded,
@@ -37,11 +37,11 @@ where
     let inner;
     let right = match right {
         Bound::Included(right) => {
-            inner = BoundCodec::bytes_encode(right).ok_or(heed::Error::Encoding)?;
+            inner = BoundCodec::bytes_encode(right).map_err(heed::Error::Encoding)?;
             Bound::Included(inner.as_ref())
         }
         Bound::Excluded(right) => {
-            inner = BoundCodec::bytes_encode(right).ok_or(heed::Error::Encoding)?;
+            inner = BoundCodec::bytes_encode(right).map_err(heed::Error::Encoding)?;
             Bound::Excluded(inner.as_ref())
         }
         Bound::Unbounded => Bound::Unbounded,
diff --git a/milli/src/search/facet/mod.rs b/milli/src/search/facet/mod.rs
index ebc9e1da0..0572d7297 100644
--- a/milli/src/search/facet/mod.rs
+++ b/milli/src/search/facet/mod.rs
@@ -22,8 +22,10 @@ fn facet_extreme_value<'t>(
     let extreme_value =
         if let Some(extreme_value) = extreme_it.next() { extreme_value } else { return Ok(None) };
     let (_, extreme_value) = extreme_value?;
-
-    Ok(OrderedF64Codec::bytes_decode(extreme_value))
+    OrderedF64Codec::bytes_decode(extreme_value)
+        .map(Some)
+        .map_err(heed::Error::Decoding)
+        .map_err(Into::into)
 }
 
 pub fn facet_min_value<'t>(
@@ -60,13 +62,12 @@ where
     let mut level0prefix = vec![];
     level0prefix.extend_from_slice(&field_id.to_be_bytes());
     level0prefix.push(0);
-    let mut level0_iter_forward = db
-        .as_polymorph()
-        .prefix_iter::<_, ByteSlice, DecodeIgnore>(txn, level0prefix.as_slice())?;
+    let mut level0_iter_forward =
+        db.remap_types::<ByteSlice, DecodeIgnore>().prefix_iter(txn, level0prefix.as_slice())?;
     if let Some(first) = level0_iter_forward.next() {
         let (first_key, _) = first?;
         let first_key = FacetGroupKeyCodec::<BoundCodec>::bytes_decode(first_key)
-            .ok_or(heed::Error::Encoding)?;
+            .map_err(heed::Error::Decoding)?;
         Ok(Some(first_key.left_bound))
     } else {
         Ok(None)
@@ -86,12 +87,12 @@ where
     level0prefix.extend_from_slice(&field_id.to_be_bytes());
     level0prefix.push(0);
     let mut level0_iter_backward = db
-        .as_polymorph()
-        .rev_prefix_iter::<_, ByteSlice, DecodeIgnore>(txn, level0prefix.as_slice())?;
+        .remap_types::<ByteSlice, DecodeIgnore>()
+        .rev_prefix_iter(txn, level0prefix.as_slice())?;
     if let Some(last) = level0_iter_backward.next() {
         let (last_key, _) = last?;
         let last_key = FacetGroupKeyCodec::<BoundCodec>::bytes_decode(last_key)
-            .ok_or(heed::Error::Encoding)?;
+            .map_err(heed::Error::Decoding)?;
         Ok(Some(last_key.left_bound))
     } else {
         Ok(None)
@@ -106,8 +107,8 @@ pub(crate) fn get_highest_level<'t>(
 ) -> heed::Result<u8> {
     let field_id_prefix = &field_id.to_be_bytes();
     Ok(db
-        .as_polymorph()
-        .rev_prefix_iter::<_, ByteSlice, DecodeIgnore>(txn, field_id_prefix)?
+        .remap_types::<ByteSlice, DecodeIgnore>()
+        .rev_prefix_iter(txn, field_id_prefix)?
         .next()
         .map(|el| {
             let (key, _) = el.unwrap();
diff --git a/milli/src/search/mod.rs b/milli/src/search/mod.rs
index 786b565ae..ee8cd1faf 100644
--- a/milli/src/search/mod.rs
+++ b/milli/src/search/mod.rs
@@ -17,8 +17,7 @@ use crate::error::UserError;
 use crate::heed_codec::facet::{FacetGroupKey, FacetGroupValue};
 use crate::score_details::{ScoreDetails, ScoringStrategy};
 use crate::{
-    execute_search, AscDesc, DefaultSearchLogger, DocumentId, FieldId, Index, Result,
-    SearchContext, BEU16,
+    execute_search, AscDesc, DefaultSearchLogger, DocumentId, FieldId, Index, Result, SearchContext,
 };
 
 // Building these factories is not free.
@@ -299,7 +298,7 @@ impl<'a> SearchForFacetValues<'a> {
             None => return Ok(Vec::new()),
         };
 
-        let fst = match self.search_query.index.facet_id_string_fst.get(rtxn, &BEU16::new(fid))? {
+        let fst = match self.search_query.index.facet_id_string_fst.get(rtxn, &fid)? {
             Some(fst) => fst,
             None => return Ok(vec![]),
         };
diff --git a/milli/src/search/new/db_cache.rs b/milli/src/search/new/db_cache.rs
index 2c670658d..5a74bc201 100644
--- a/milli/src/search/new/db_cache.rs
+++ b/milli/src/search/new/db_cache.rs
@@ -63,12 +63,14 @@ impl<'ctx> DatabaseCache<'ctx> {
         }
 
         match cache.get(&cache_key).unwrap() {
-            Some(Cow::Borrowed(bytes)) => {
-                DC::bytes_decode_owned(bytes).ok_or(heed::Error::Decoding.into()).map(Some)
-            }
-            Some(Cow::Owned(bytes)) => {
-                DC::bytes_decode_owned(bytes).ok_or(heed::Error::Decoding.into()).map(Some)
-            }
+            Some(Cow::Borrowed(bytes)) => DC::bytes_decode_owned(bytes)
+                .map_err(heed::Error::Decoding)
+                .map_err(Into::into)
+                .map(Some),
+            Some(Cow::Owned(bytes)) => DC::bytes_decode_owned(bytes)
+                .map_err(heed::Error::Decoding)
+                .map_err(Into::into)
+                .map(Some),
             None => Ok(None),
         }
     }
@@ -110,12 +112,14 @@ impl<'ctx> DatabaseCache<'ctx> {
         }
 
         match cache.get(&cache_key).unwrap() {
-            Some(Cow::Borrowed(bytes)) => {
-                DC::bytes_decode_owned(bytes).ok_or(heed::Error::Decoding.into()).map(Some)
-            }
-            Some(Cow::Owned(bytes)) => {
-                DC::bytes_decode_owned(bytes).ok_or(heed::Error::Decoding.into()).map(Some)
-            }
+            Some(Cow::Borrowed(bytes)) => DC::bytes_decode_owned(bytes)
+                .map_err(heed::Error::Decoding)
+                .map_err(Into::into)
+                .map(Some),
+            Some(Cow::Owned(bytes)) => DC::bytes_decode_owned(bytes)
+                .map_err(heed::Error::Decoding)
+                .map_err(Into::into)
+                .map(Some),
             None => Ok(None),
         }
     }
diff --git a/milli/src/search/new/mod.rs b/milli/src/search/new/mod.rs
index 6ceb78223..60386258e 100644
--- a/milli/src/search/new/mod.rs
+++ b/milli/src/search/new/mod.rs
@@ -50,9 +50,7 @@ use crate::distance::NDotProductPoint;
 use crate::error::FieldIdMapMissingEntry;
 use crate::score_details::{ScoreDetails, ScoringStrategy};
 use crate::search::new::distinct::apply_distinct_rule;
-use crate::{
-    AscDesc, DocumentId, Filter, Index, Member, Result, TermsMatchingStrategy, UserError, BEU32,
-};
+use crate::{AscDesc, DocumentId, Filter, Index, Member, Result, TermsMatchingStrategy, UserError};
 
 /// A structure used throughout the execution of a search query.
 pub struct SearchContext<'ctx> {
@@ -451,8 +449,8 @@ pub fn execute_search(
                 let mut docids = Vec::new();
                 let mut uniq_docids = RoaringBitmap::new();
                 for instant_distance::Item { distance: _, pid, point: _ } in neighbors {
-                    let index = BEU32::new(pid.into_inner());
-                    let docid = ctx.index.vector_id_docid.get(ctx.txn, &index)?.unwrap().get();
+                    let index = pid.into_inner();
+                    let docid = ctx.index.vector_id_docid.get(ctx.txn, &index)?.unwrap();
                     if universe.contains(docid) && uniq_docids.insert(docid) {
                         docids.push(docid);
                         if docids.len() == (from + length) {
diff --git a/milli/src/update/clear_documents.rs b/milli/src/update/clear_documents.rs
index afe0191b1..59adda3e8 100644
--- a/milli/src/update/clear_documents.rs
+++ b/milli/src/update/clear_documents.rs
@@ -1,15 +1,16 @@
+use heed::RwTxn;
 use roaring::RoaringBitmap;
 use time::OffsetDateTime;
 
 use crate::{FieldDistribution, Index, Result};
 
-pub struct ClearDocuments<'t, 'u, 'i> {
-    wtxn: &'t mut heed::RwTxn<'i, 'u>,
+pub struct ClearDocuments<'t, 'i> {
+    wtxn: &'t mut RwTxn<'i>,
     index: &'i Index,
 }
 
-impl<'t, 'u, 'i> ClearDocuments<'t, 'u, 'i> {
-    pub fn new(wtxn: &'t mut heed::RwTxn<'i, 'u>, index: &'i Index) -> ClearDocuments<'t, 'u, 'i> {
+impl<'t, 'i> ClearDocuments<'t, 'i> {
+    pub fn new(wtxn: &'t mut RwTxn<'i>, index: &'i Index) -> ClearDocuments<'t, 'i> {
         ClearDocuments { wtxn, index }
     }
 
diff --git a/milli/src/update/facet/bulk.rs b/milli/src/update/facet/bulk.rs
index 5626a4aae..bfee002fd 100644
--- a/milli/src/update/facet/bulk.rs
+++ b/milli/src/update/facet/bulk.rs
@@ -3,7 +3,7 @@ use std::io::BufReader;
 
 use grenad::CompressionType;
 use heed::types::ByteSlice;
-use heed::{BytesDecode, BytesEncode, Error, RoTxn, RwTxn};
+use heed::{BytesDecode, BytesEncode, Error, PutFlags, RoTxn, RwTxn};
 use roaring::RoaringBitmap;
 
 use super::{FACET_GROUP_SIZE, FACET_MIN_LEVEL_SIZE};
@@ -146,7 +146,13 @@ impl<R: std::io::Read + std::io::Seek> FacetsUpdateBulkInner<R> {
                 buffer.push(1);
                 // then we extend the buffer with the docids bitmap
                 buffer.extend_from_slice(value);
-                unsafe { database.append(key, &buffer)? };
+                unsafe {
+                    database.put_current_with_options::<ByteSlice>(
+                        PutFlags::APPEND,
+                        key,
+                        &buffer,
+                    )?
+                };
             }
         } else {
             let mut buffer = Vec::new();
@@ -219,8 +225,8 @@ impl<R: std::io::Read + std::io::Seek> FacetsUpdateBulkInner<R> {
 
         let level_0_iter = self
             .db
-            .as_polymorph()
-            .prefix_iter::<_, ByteSlice, ByteSlice>(rtxn, level_0_prefix.as_slice())?
+            .remap_types::<ByteSlice, ByteSlice>()
+            .prefix_iter(rtxn, level_0_prefix.as_slice())?
             .remap_types::<FacetGroupKeyCodec<ByteSliceRefCodec>, FacetGroupValueCodec>();
 
         let mut left_bound: &[u8] = &[];
@@ -308,10 +314,10 @@ impl<R: std::io::Read + std::io::Seek> FacetsUpdateBulkInner<R> {
                 {
                     let key = FacetGroupKey { field_id, level, left_bound };
                     let key = FacetGroupKeyCodec::<ByteSliceRefCodec>::bytes_encode(&key)
-                        .ok_or(Error::Encoding)?;
+                        .map_err(Error::Encoding)?;
                     let value = FacetGroupValue { size: group_size, bitmap };
                     let value =
-                        FacetGroupValueCodec::bytes_encode(&value).ok_or(Error::Encoding)?;
+                        FacetGroupValueCodec::bytes_encode(&value).map_err(Error::Encoding)?;
                     cur_writer.insert(key, value)?;
                     cur_writer_len += 1;
                 }
@@ -337,9 +343,9 @@ impl<R: std::io::Read + std::io::Seek> FacetsUpdateBulkInner<R> {
             {
                 let key = FacetGroupKey { field_id, level, left_bound };
                 let key = FacetGroupKeyCodec::<ByteSliceRefCodec>::bytes_encode(&key)
-                    .ok_or(Error::Encoding)?;
+                    .map_err(Error::Encoding)?;
                 let value = FacetGroupValue { size: group_size, bitmap };
-                let value = FacetGroupValueCodec::bytes_encode(&value).ok_or(Error::Encoding)?;
+                let value = FacetGroupValueCodec::bytes_encode(&value).map_err(Error::Encoding)?;
                 cur_writer.insert(key, value)?;
                 cur_writer_len += 1;
             }
diff --git a/milli/src/update/facet/incremental.rs b/milli/src/update/facet/incremental.rs
index e241c499c..dc47ca126 100644
--- a/milli/src/update/facet/incremental.rs
+++ b/milli/src/update/facet/incremental.rs
@@ -68,18 +68,18 @@ impl FacetsUpdateIncremental {
                 continue;
             }
             let key = FacetGroupKeyCodec::<ByteSliceRefCodec>::bytes_decode(key)
-                .ok_or(heed::Error::Encoding)?;
+                .map_err(heed::Error::Encoding)?;
             let value = KvReader::new(value);
 
             let docids_to_delete = value
                 .get(DelAdd::Deletion)
                 .map(CboRoaringBitmapCodec::bytes_decode)
-                .map(|o| o.ok_or(heed::Error::Encoding));
+                .map(|o| o.map_err(heed::Error::Encoding));
 
             let docids_to_add = value
                 .get(DelAdd::Addition)
                 .map(CboRoaringBitmapCodec::bytes_decode)
-                .map(|o| o.ok_or(heed::Error::Encoding));
+                .map(|o| o.map_err(heed::Error::Encoding));
 
             if let Some(docids_to_delete) = docids_to_delete {
                 let docids_to_delete = docids_to_delete?;
@@ -134,15 +134,14 @@ impl FacetsUpdateIncrementalInner {
                     prefix.extend_from_slice(&field_id.to_be_bytes());
                     prefix.push(level);
 
-                    let mut iter =
-                        self.db.as_polymorph().prefix_iter::<_, ByteSlice, FacetGroupValueCodec>(
-                            txn,
-                            prefix.as_slice(),
-                        )?;
+                    let mut iter = self
+                        .db
+                        .remap_types::<ByteSlice, FacetGroupValueCodec>()
+                        .prefix_iter(txn, prefix.as_slice())?;
                     let (key_bytes, value) = iter.next().unwrap()?;
                     Ok((
                         FacetGroupKeyCodec::<ByteSliceRefCodec>::bytes_decode(key_bytes)
-                            .ok_or(Error::Encoding)?
+                            .map_err(Error::Encoding)?
                             .into_owned(),
                         value,
                     ))
@@ -177,10 +176,8 @@ impl FacetsUpdateIncrementalInner {
         level0_prefix.extend_from_slice(&field_id.to_be_bytes());
         level0_prefix.push(0);
 
-        let mut iter = self
-            .db
-            .as_polymorph()
-            .prefix_iter::<_, ByteSlice, DecodeIgnore>(txn, &level0_prefix)?;
+        let mut iter =
+            self.db.remap_types::<ByteSlice, DecodeIgnore>().prefix_iter(txn, &level0_prefix)?;
 
         if iter.next().is_none() {
             drop(iter);
@@ -384,8 +381,8 @@ impl FacetsUpdateIncrementalInner {
 
         let size_highest_level = self
             .db
-            .as_polymorph()
-            .prefix_iter::<_, ByteSlice, ByteSlice>(txn, &highest_level_prefix)?
+            .remap_types::<ByteSlice, ByteSlice>()
+            .prefix_iter(txn, &highest_level_prefix)?
             .count();
 
         if size_highest_level < self.group_size as usize * self.min_level_size as usize {
@@ -394,8 +391,8 @@ impl FacetsUpdateIncrementalInner {
 
         let mut groups_iter = self
             .db
-            .as_polymorph()
-            .prefix_iter::<_, ByteSlice, FacetGroupValueCodec>(txn, &highest_level_prefix)?;
+            .remap_types::<ByteSlice, FacetGroupValueCodec>()
+            .prefix_iter(txn, &highest_level_prefix)?;
 
         let nbr_new_groups = size_highest_level / self.group_size as usize;
         let nbr_leftover_elements = size_highest_level % self.group_size as usize;
@@ -407,7 +404,7 @@ impl FacetsUpdateIncrementalInner {
             for _ in 0..group_size {
                 let (key_bytes, value_i) = groups_iter.next().unwrap()?;
                 let key_i = FacetGroupKeyCodec::<ByteSliceRefCodec>::bytes_decode(key_bytes)
-                    .ok_or(Error::Encoding)?;
+                    .map_err(Error::Encoding)?;
 
                 if first_key.is_none() {
                     first_key = Some(key_i);
@@ -430,7 +427,7 @@ impl FacetsUpdateIncrementalInner {
             for _ in 0..nbr_leftover_elements {
                 let (key_bytes, value_i) = groups_iter.next().unwrap()?;
                 let key_i = FacetGroupKeyCodec::<ByteSliceRefCodec>::bytes_decode(key_bytes)
-                    .ok_or(Error::Encoding)?;
+                    .map_err(Error::Encoding)?;
 
                 if first_key.is_none() {
                     first_key = Some(key_i);
@@ -597,8 +594,8 @@ impl FacetsUpdateIncrementalInner {
         if highest_level == 0
             || self
                 .db
-                .as_polymorph()
-                .prefix_iter::<_, ByteSlice, ByteSlice>(txn, &highest_level_prefix)?
+                .remap_types::<ByteSlice, ByteSlice>()
+                .prefix_iter(txn, &highest_level_prefix)?
                 .count()
                 >= self.min_level_size as usize
         {
@@ -607,13 +604,13 @@ impl FacetsUpdateIncrementalInner {
         let mut to_delete = vec![];
         let mut iter = self
             .db
-            .as_polymorph()
-            .prefix_iter::<_, ByteSlice, ByteSlice>(txn, &highest_level_prefix)?;
+            .remap_types::<ByteSlice, ByteSlice>()
+            .prefix_iter(txn, &highest_level_prefix)?;
         for el in iter.by_ref() {
             let (k, _) = el?;
             to_delete.push(
                 FacetGroupKeyCodec::<ByteSliceRefCodec>::bytes_decode(k)
-                    .ok_or(Error::Encoding)?
+                    .map_err(Error::Encoding)?
                     .into_owned(),
             );
         }
diff --git a/milli/src/update/facet/mod.rs b/milli/src/update/facet/mod.rs
index 52fea0f5f..9c1d2a370 100644
--- a/milli/src/update/facet/mod.rs
+++ b/milli/src/update/facet/mod.rs
@@ -95,7 +95,7 @@ use crate::heed_codec::facet::{FacetGroupKey, FacetGroupKeyCodec, FacetGroupValu
 use crate::heed_codec::ByteSliceRefCodec;
 use crate::update::index_documents::create_sorter;
 use crate::update::merge_btreeset_string;
-use crate::{BEU16StrCodec, Index, Result, BEU16, MAX_FACET_VALUE_LENGTH};
+use crate::{BEU16StrCodec, Index, Result, MAX_FACET_VALUE_LENGTH};
 
 pub mod bulk;
 pub mod incremental;
@@ -207,8 +207,8 @@ impl<'i> FacetsUpdate<'i> {
                 }
                 let set = BTreeSet::from_iter(std::iter::once(left_bound));
                 let key = (field_id, normalized_facet.as_ref());
-                let key = BEU16StrCodec::bytes_encode(&key).ok_or(heed::Error::Encoding)?;
-                let val = SerdeJson::bytes_encode(&set).ok_or(heed::Error::Encoding)?;
+                let key = BEU16StrCodec::bytes_encode(&key).map_err(heed::Error::Encoding)?;
+                let val = SerdeJson::bytes_encode(&set).map_err(heed::Error::Encoding)?;
                 sorter.insert(key, val)?;
             }
         }
@@ -252,7 +252,7 @@ impl<'i> FacetsUpdate<'i> {
 
         // We write those FSTs in LMDB now
         for (field_id, fst) in text_fsts {
-            self.index.facet_id_string_fst.put(wtxn, &BEU16::new(field_id), &fst)?;
+            self.index.facet_id_string_fst.put(wtxn, &field_id, &fst)?;
         }
 
         Ok(())
diff --git a/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs b/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs
index 3fcec3e79..b7de1e621 100644
--- a/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs
+++ b/milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs
@@ -6,8 +6,8 @@ use std::io::{self, BufReader};
 use std::mem::size_of;
 use std::result::Result as StdResult;
 
+use bytemuck::bytes_of;
 use grenad::Sorter;
-use heed::zerocopy::AsBytes;
 use heed::BytesEncode;
 use itertools::EitherOrBoth;
 use ordered_float::OrderedFloat;
@@ -20,9 +20,7 @@ use crate::error::InternalError;
 use crate::facet::value_encoding::f64_into_bytes;
 use crate::update::del_add::{DelAdd, KvWriterDelAdd};
 use crate::update::index_documents::{create_writer, writer_into_reader};
-use crate::{
-    CboRoaringBitmapCodec, DocumentId, Error, FieldId, Result, BEU32, MAX_FACET_VALUE_LENGTH,
-};
+use crate::{CboRoaringBitmapCodec, DocumentId, Error, FieldId, Result, MAX_FACET_VALUE_LENGTH};
 
 /// The length of the elements that are always in the buffer when inserting new values.
 const TRUNCATE_SIZE: usize = size_of::<FieldId>() + size_of::<DocumentId>();
@@ -94,7 +92,7 @@ pub fn extract_fid_docid_facet_values<R: io::Read + io::Seek>(
                 strings_key_buffer.extend_from_slice(&field_id.to_be_bytes());
 
                 let document: [u8; 4] = docid_bytes[..4].try_into().ok().unwrap();
-                let document = BEU32::from(document).get();
+                let document = DocumentId::from_be_bytes(document);
 
                 // For the other extraction tasks, prefix the key with the field_id and the document_id
                 numbers_key_buffer.extend_from_slice(docid_bytes);
@@ -323,7 +321,7 @@ where
                     // We insert only the Del part of the Obkv to inform
                     // that we only want to remove all those numbers.
                     let mut obkv = KvWriterDelAdd::memory();
-                    obkv.insert(DelAdd::Deletion, ().as_bytes())?;
+                    obkv.insert(DelAdd::Deletion, bytes_of(&()))?;
                     let bytes = obkv.into_inner()?;
                     fid_docid_facet_numbers_sorter.insert(&key_buffer, bytes)?;
                 }
@@ -336,7 +334,7 @@ where
                     // We insert only the Add part of the Obkv to inform
                     // that we only want to remove all those numbers.
                     let mut obkv = KvWriterDelAdd::memory();
-                    obkv.insert(DelAdd::Addition, ().as_bytes())?;
+                    obkv.insert(DelAdd::Addition, bytes_of(&()))?;
                     let bytes = obkv.into_inner()?;
                     fid_docid_facet_numbers_sorter.insert(&key_buffer, bytes)?;
                 }
diff --git a/milli/src/update/index_documents/extract/extract_word_docids.rs b/milli/src/update/index_documents/extract/extract_word_docids.rs
index f278012c7..66092821f 100644
--- a/milli/src/update/index_documents/extract/extract_word_docids.rs
+++ b/milli/src/update/index_documents/extract/extract_word_docids.rs
@@ -118,7 +118,7 @@ pub fn extract_word_docids<R: io::Read + io::Seek>(
         }
 
         let (word, fid) = StrBEU16Codec::bytes_decode(key)
-            .ok_or(SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
+            .map_err(|_| SerializationError::Decoding { db_name: Some(DOCID_WORD_POSITIONS) })?;
 
         // every words contained in an attribute set to exact must be pushed in the exact_words list.
         if exact_attributes.contains(&fid) {
diff --git a/milli/src/update/index_documents/mod.rs b/milli/src/update/index_documents/mod.rs
index 113114681..82858a09d 100644
--- a/milli/src/update/index_documents/mod.rs
+++ b/milli/src/update/index_documents/mod.rs
@@ -68,8 +68,8 @@ impl Default for IndexDocumentsMethod {
     }
 }
 
-pub struct IndexDocuments<'t, 'u, 'i, 'a, FP, FA> {
-    wtxn: &'t mut heed::RwTxn<'i, 'u>,
+pub struct IndexDocuments<'t, 'i, 'a, FP, FA> {
+    wtxn: &'t mut heed::RwTxn<'i>,
     index: &'i Index,
     config: IndexDocumentsConfig,
     indexer_config: &'a IndexerConfig,
@@ -90,19 +90,19 @@ pub struct IndexDocumentsConfig {
     pub autogenerate_docids: bool,
 }
 
-impl<'t, 'u, 'i, 'a, FP, FA> IndexDocuments<'t, 'u, 'i, 'a, FP, FA>
+impl<'t, 'i, 'a, FP, FA> IndexDocuments<'t, 'i, 'a, FP, FA>
 where
     FP: Fn(UpdateIndexingStep) + Sync,
     FA: Fn() -> bool + Sync,
 {
     pub fn new(
-        wtxn: &'t mut heed::RwTxn<'i, 'u>,
+        wtxn: &'t mut heed::RwTxn<'i>,
         index: &'i Index,
         indexer_config: &'a IndexerConfig,
         config: IndexDocumentsConfig,
         progress: FP,
         should_abort: FA,
-    ) -> Result<IndexDocuments<'t, 'u, 'i, 'a, FP, FA>> {
+    ) -> Result<IndexDocuments<'t, 'i, 'a, FP, FA>> {
         let transform = Some(Transform::new(
             wtxn,
             index,
diff --git a/milli/src/update/index_documents/transform.rs b/milli/src/update/index_documents/transform.rs
index 323bc3da7..0c70b592f 100644
--- a/milli/src/update/index_documents/transform.rs
+++ b/milli/src/update/index_documents/transform.rs
@@ -24,9 +24,7 @@ use crate::index::{db_name, main_key};
 use crate::update::del_add::{into_del_add_obkv, DelAdd, DelAddOperation, KvReaderDelAdd};
 use crate::update::index_documents::GrenadParameters;
 use crate::update::{AvailableDocumentsIds, ClearDocuments, UpdateIndexingStep};
-use crate::{
-    FieldDistribution, FieldId, FieldIdMapMissingEntry, FieldsIdsMap, Index, Result, BEU32,
-};
+use crate::{FieldDistribution, FieldId, FieldIdMapMissingEntry, FieldsIdsMap, Index, Result};
 
 pub struct TransformOutput {
     pub primary_key: String,
@@ -245,7 +243,7 @@ impl<'a, 'i> Transform<'a, 'i> {
 
             let mut skip_insertion = false;
             if let Some(original_docid) = original_docid {
-                let original_key = BEU32::new(original_docid);
+                let original_key = original_docid;
                 let base_obkv = self
                     .index
                     .documents
@@ -499,7 +497,7 @@ impl<'a, 'i> Transform<'a, 'i> {
         self.replaced_documents_ids.insert(internal_docid);
 
         // fetch the obkv document
-        let original_key = BEU32::new(internal_docid);
+        let original_key = internal_docid;
         let base_obkv = self
             .index
             .documents
@@ -811,7 +809,7 @@ impl<'a, 'i> Transform<'a, 'i> {
     // TODO this can be done in parallel by using the rayon `ThreadPool`.
     pub fn prepare_for_documents_reindexing(
         self,
-        wtxn: &mut heed::RwTxn<'i, '_>,
+        wtxn: &mut heed::RwTxn<'i>,
         old_fields_ids_map: FieldsIdsMap,
         mut new_fields_ids_map: FieldsIdsMap,
     ) -> Result<TransformOutput> {
@@ -857,7 +855,6 @@ impl<'a, 'i> Transform<'a, 'i> {
             let obkv = self.index.documents.get(wtxn, &docid)?.ok_or(
                 InternalError::DatabaseMissingEntry { db_name: db_name::DOCUMENTS, key: None },
             )?;
-            let docid = docid.get();
 
             obkv_buffer.clear();
             let mut obkv_writer = KvWriter::<_, FieldId>::new(&mut obkv_buffer);
diff --git a/milli/src/update/index_documents/typed_chunk.rs b/milli/src/update/index_documents/typed_chunk.rs
index 4f9f0ef6f..6ec00caae 100644
--- a/milli/src/update/index_documents/typed_chunk.rs
+++ b/milli/src/update/index_documents/typed_chunk.rs
@@ -7,7 +7,7 @@ use bytemuck::allocation::pod_collect_to_vec;
 use charabia::{Language, Script};
 use grenad::MergerBuilder;
 use heed::types::ByteSlice;
-use heed::RwTxn;
+use heed::{PutFlags, RwTxn};
 use log::error;
 use obkv::{KvReader, KvWriter};
 use ordered_float::OrderedFloat;
@@ -27,9 +27,7 @@ use crate::index::Hnsw;
 use crate::update::del_add::{deladd_serialize_add_side, DelAdd, KvReaderDelAdd};
 use crate::update::facet::FacetsUpdate;
 use crate::update::index_documents::helpers::{as_cloneable_grenad, try_split_array_at};
-use crate::{
-    lat_lng_to_xyz, DocumentId, FieldId, GeoPoint, Index, Result, SerializationError, BEU32,
-};
+use crate::{lat_lng_to_xyz, DocumentId, FieldId, GeoPoint, Index, Result, SerializationError};
 
 pub(crate) enum TypedChunk {
     FieldIdDocidFacetStrings(grenad::Reader<CursorClonableMmap>),
@@ -149,7 +147,7 @@ pub(crate) fn write_typed_chunk_into_index(
                 let db = index.documents.remap_data_type::<ByteSlice>();
 
                 if !writer.is_empty() {
-                    db.put(wtxn, &BEU32::new(docid), &writer.into_inner().unwrap())?;
+                    db.put(wtxn, &docid, &writer.into_inner().unwrap())?;
                     operations.push(DocumentOperation {
                         external_id: external_id.to_string(),
                         internal_id: docid,
@@ -157,7 +155,7 @@ pub(crate) fn write_typed_chunk_into_index(
                     });
                     docids.insert(docid);
                 } else {
-                    db.delete(wtxn, &BEU32::new(docid))?;
+                    db.delete(wtxn, &docid)?;
                     operations.push(DocumentOperation {
                         external_id: external_id.to_string(),
                         internal_id: docid,
@@ -362,8 +360,8 @@ pub(crate) fn write_typed_chunk_into_index(
             // We extract and store the previous vectors
             if let Some(hnsw) = index.vector_hnsw(wtxn)? {
                 for (pid, point) in hnsw.iter() {
-                    let pid_key = BEU32::new(pid.into_inner());
-                    let docid = index.vector_id_docid.get(wtxn, &pid_key)?.unwrap().get();
+                    let pid_key = pid.into_inner();
+                    let docid = index.vector_id_docid.get(wtxn, &pid_key)?.unwrap();
                     let vector: Vec<_> = point.iter().copied().map(OrderedFloat).collect();
                     vectors_set.insert((docid, vector));
                 }
@@ -424,11 +422,7 @@ pub(crate) fn write_typed_chunk_into_index(
             // Store the vectors in the point-docid relation database
             index.vector_id_docid.clear(wtxn)?;
             for (docid, pid) in docids.into_iter().zip(pids) {
-                index.vector_id_docid.put(
-                    wtxn,
-                    &BEU32::new(pid.into_inner()),
-                    &BEU32::new(docid),
-                )?;
+                index.vector_id_docid.put(wtxn, &pid.into_inner(), &docid)?;
             }
 
             log::debug!("There are {} entries in the HNSW so far", hnsw_length);
@@ -568,14 +562,17 @@ where
     while let Some((key, value)) = cursor.move_on_next()? {
         if valid_lmdb_key(key) {
             debug_assert!(
-                K::bytes_decode(key).is_some(),
+                K::bytes_decode(key).is_ok(),
                 "Couldn't decode key with the database decoder, key length: {} - key bytes: {:x?}",
                 key.len(),
                 &key
             );
             buffer.clear();
             let value = serialize_value(value, &mut buffer)?;
-            unsafe { database.append(key, value)? };
+            unsafe {
+                // safety: We do not keep a reference to anything that lives inside the database
+                database.put_current_with_options::<ByteSlice>(PutFlags::APPEND, key, value)?
+            };
         }
     }
 
diff --git a/milli/src/update/settings.rs b/milli/src/update/settings.rs
index fd7ffa760..926c89cf5 100644
--- a/milli/src/update/settings.rs
+++ b/milli/src/update/settings.rs
@@ -100,8 +100,8 @@ impl<'de, T: Deserialize<'de>> Deserialize<'de> for Setting<T> {
     }
 }
 
-pub struct Settings<'a, 't, 'u, 'i> {
-    wtxn: &'t mut heed::RwTxn<'i, 'u>,
+pub struct Settings<'a, 't, 'i> {
+    wtxn: &'t mut heed::RwTxn<'i>,
     index: &'i Index,
 
     indexer_config: &'a IndexerConfig,
@@ -129,12 +129,12 @@ pub struct Settings<'a, 't, 'u, 'i> {
     pagination_max_total_hits: Setting<usize>,
 }
 
-impl<'a, 't, 'u, 'i> Settings<'a, 't, 'u, 'i> {
+impl<'a, 't, 'i> Settings<'a, 't, 'i> {
     pub fn new(
-        wtxn: &'t mut heed::RwTxn<'i, 'u>,
+        wtxn: &'t mut heed::RwTxn<'i>,
         index: &'i Index,
         indexer_config: &'a IndexerConfig,
-    ) -> Settings<'a, 't, 'u, 'i> {
+    ) -> Settings<'a, 't, 'i> {
         Settings {
             wtxn,
             index,
diff --git a/milli/src/update/word_prefix_docids.rs b/milli/src/update/word_prefix_docids.rs
index 618f451dc..5d60c3765 100644
--- a/milli/src/update/word_prefix_docids.rs
+++ b/milli/src/update/word_prefix_docids.rs
@@ -12,8 +12,8 @@ use crate::update::index_documents::{
 };
 use crate::{CboRoaringBitmapCodec, Result};
 
-pub struct WordPrefixDocids<'t, 'u, 'i> {
-    wtxn: &'t mut heed::RwTxn<'i, 'u>,
+pub struct WordPrefixDocids<'t, 'i> {
+    wtxn: &'t mut heed::RwTxn<'i>,
     word_docids: Database<Str, CboRoaringBitmapCodec>,
     word_prefix_docids: Database<Str, CboRoaringBitmapCodec>,
     pub(crate) chunk_compression_type: CompressionType,
@@ -22,12 +22,12 @@ pub struct WordPrefixDocids<'t, 'u, 'i> {
     pub(crate) max_memory: Option<usize>,
 }
 
-impl<'t, 'u, 'i> WordPrefixDocids<'t, 'u, 'i> {
+impl<'t, 'i> WordPrefixDocids<'t, 'i> {
     pub fn new(
-        wtxn: &'t mut heed::RwTxn<'i, 'u>,
+        wtxn: &'t mut heed::RwTxn<'i>,
         word_docids: Database<Str, CboRoaringBitmapCodec>,
         word_prefix_docids: Database<Str, CboRoaringBitmapCodec>,
-    ) -> WordPrefixDocids<'t, 'u, 'i> {
+    ) -> WordPrefixDocids<'t, 'i> {
         WordPrefixDocids {
             wtxn,
             word_docids,
diff --git a/milli/src/update/words_prefix_integer_docids.rs b/milli/src/update/words_prefix_integer_docids.rs
index e083f510a..a763ecaeb 100644
--- a/milli/src/update/words_prefix_integer_docids.rs
+++ b/milli/src/update/words_prefix_integer_docids.rs
@@ -17,8 +17,8 @@ use crate::update::index_documents::{
 };
 use crate::{CboRoaringBitmapCodec, Result};
 
-pub struct WordPrefixIntegerDocids<'t, 'u, 'i> {
-    wtxn: &'t mut heed::RwTxn<'i, 'u>,
+pub struct WordPrefixIntegerDocids<'t, 'i> {
+    wtxn: &'t mut heed::RwTxn<'i>,
     prefix_database: Database<StrBEU16Codec, CboRoaringBitmapCodec>,
     word_database: Database<StrBEU16Codec, CboRoaringBitmapCodec>,
     pub(crate) chunk_compression_type: CompressionType,
@@ -27,12 +27,12 @@ pub struct WordPrefixIntegerDocids<'t, 'u, 'i> {
     pub(crate) max_memory: Option<usize>,
 }
 
-impl<'t, 'u, 'i> WordPrefixIntegerDocids<'t, 'u, 'i> {
+impl<'t, 'i> WordPrefixIntegerDocids<'t, 'i> {
     pub fn new(
-        wtxn: &'t mut heed::RwTxn<'i, 'u>,
+        wtxn: &'t mut heed::RwTxn<'i>,
         prefix_database: Database<StrBEU16Codec, CboRoaringBitmapCodec>,
         word_database: Database<StrBEU16Codec, CboRoaringBitmapCodec>,
-    ) -> WordPrefixIntegerDocids<'t, 'u, 'i> {
+    ) -> WordPrefixIntegerDocids<'t, 'i> {
         WordPrefixIntegerDocids {
             wtxn,
             prefix_database,
@@ -72,7 +72,8 @@ impl<'t, 'u, 'i> WordPrefixIntegerDocids<'t, 'u, 'i> {
             let mut current_prefixes: Option<&&[String]> = None;
             let mut prefixes_cache = HashMap::new();
             while let Some((key, data)) = new_word_integer_docids_iter.move_on_next()? {
-                let (word, pos) = StrBEU16Codec::bytes_decode(key).ok_or(heed::Error::Decoding)?;
+                let (word, pos) =
+                    StrBEU16Codec::bytes_decode(key).map_err(heed::Error::Decoding)?;
 
                 current_prefixes = match current_prefixes.take() {
                     Some(prefixes) if word.starts_with(&prefixes[0]) => Some(prefixes),
diff --git a/milli/src/update/words_prefixes_fst.rs b/milli/src/update/words_prefixes_fst.rs
index 121b45c4a..f26bf93e5 100644
--- a/milli/src/update/words_prefixes_fst.rs
+++ b/milli/src/update/words_prefixes_fst.rs
@@ -2,21 +2,19 @@ use std::iter::{repeat_with, FromIterator};
 use std::str;
 
 use fst::{SetBuilder, Streamer};
+use heed::RwTxn;
 
 use crate::{Index, Result, SmallString32};
 
-pub struct WordsPrefixesFst<'t, 'u, 'i> {
-    wtxn: &'t mut heed::RwTxn<'i, 'u>,
+pub struct WordsPrefixesFst<'t, 'i> {
+    wtxn: &'t mut RwTxn<'i>,
     index: &'i Index,
     threshold: u32,
     max_prefix_length: usize,
 }
 
-impl<'t, 'u, 'i> WordsPrefixesFst<'t, 'u, 'i> {
-    pub fn new(
-        wtxn: &'t mut heed::RwTxn<'i, 'u>,
-        index: &'i Index,
-    ) -> WordsPrefixesFst<'t, 'u, 'i> {
+impl<'t, 'i> WordsPrefixesFst<'t, 'i> {
+    pub fn new(wtxn: &'t mut RwTxn<'i>, index: &'i Index) -> WordsPrefixesFst<'t, 'i> {
         WordsPrefixesFst { wtxn, index, threshold: 100, max_prefix_length: 4 }
     }