Introduce the ConcurrentAvailableIds struct and rename the other to AvailableIds

milli/src/update/available_ids.rs

@@ -3,12 +3,12 @@ use std::ops::RangeInclusive;
 
 use roaring::bitmap::{IntoIter, RoaringBitmap};
 
-pub struct AvailableDocumentsIds {
+pub struct AvailableIds {
     iter: Chain<IntoIter, RangeInclusive<u32>>,
 }
 
-impl AvailableDocumentsIds {
-    pub fn from_documents_ids(docids: &RoaringBitmap) -> AvailableDocumentsIds {
+impl AvailableIds {
+    pub fn new(docids: &RoaringBitmap) -> AvailableIds {
         match docids.max() {
             Some(last_id) => {
                 let mut available = RoaringBitmap::from_iter(0..last_id);
@@ -20,17 +20,17 @@ impl AvailableDocumentsIds {
                     None => 1..=0, // empty range iterator
                 };
 
-                AvailableDocumentsIds { iter: available.into_iter().chain(iter) }
+                AvailableIds { iter: available.into_iter().chain(iter) }
             }
             None => {
                 let empty = RoaringBitmap::new().into_iter();
-                AvailableDocumentsIds { iter: empty.chain(0..=u32::MAX) }
+                AvailableIds { iter: empty.chain(0..=u32::MAX) }
             }
         }
     }
 }
 
-impl Iterator for AvailableDocumentsIds {
+impl Iterator for AvailableIds {
     type Item = u32;
 
     fn next(&mut self) -> Option<Self::Item> {
@@ -45,7 +45,7 @@ mod tests {
     #[test]
     fn empty() {
         let base = RoaringBitmap::new();
-        let left = AvailableDocumentsIds::from_documents_ids(&base);
+        let left = AvailableIds::new(&base);
         let right = 0..=u32::MAX;
         left.zip(right).take(500).for_each(|(l, r)| assert_eq!(l, r));
     }
@@ -58,7 +58,7 @@ mod tests {
         base.insert(100);
         base.insert(405);
 
-        let left = AvailableDocumentsIds::from_documents_ids(&base);
+        let left = AvailableIds::new(&base);
         let right = (0..=u32::MAX).filter(|&n| n != 0 && n != 10 && n != 100 && n != 405);
         left.zip(right).take(500).for_each(|(l, r)| assert_eq!(l, r));
     }

milli/src/update/concurrent_available_ids.rs

@@ -0,0 +1,59 @@
+use std::sync::atomic::{AtomicBool, AtomicU32, AtomicU64, Ordering};
+
+use roaring::RoaringBitmap;
+
+/// A concurrent ID generate that will never return the same ID twice.
+#[derive(Debug)]
+pub struct ConcurrentAvailableIds {
+    /// The current tree node ID we should use if there is no other IDs available.
+    current: AtomicU32,
+    /// The total number of tree node IDs used.
+    used: AtomicU64,
+
+    /// A list of IDs to exhaust before picking IDs from `current`.
+    available: RoaringBitmap,
+    /// The current Nth ID to select in the bitmap.
+    select_in_bitmap: AtomicU32,
+    /// Tells if you should look in the roaring bitmap or if all the IDs are already exhausted.
+    look_into_bitmap: AtomicBool,
+}
+
+impl ConcurrentAvailableIds {
+    /// Creates an ID generator returning unique IDs, avoiding the specified used IDs.
+    pub fn new(used: RoaringBitmap) -> ConcurrentAvailableIds {
+        let last_id = used.max().map_or(0, |id| id + 1);
+        let used_ids = used.len();
+        let available = RoaringBitmap::from_sorted_iter(0..last_id).unwrap() - used;
+
+        ConcurrentAvailableIds {
+            current: AtomicU32::new(last_id),
+            used: AtomicU64::new(used_ids),
+            select_in_bitmap: AtomicU32::new(0),
+            look_into_bitmap: AtomicBool::new(!available.is_empty()),
+            available,
+        }
+    }
+
+    /// Returns a new unique ID and increase the count of IDs used.
+    pub fn next(&self) -> Option<u32> {
+        if self.used.fetch_add(1, Ordering::Relaxed) > u32::MAX as u64 {
+            None
+        } else if self.look_into_bitmap.load(Ordering::Relaxed) {
+            let current = self.select_in_bitmap.fetch_add(1, Ordering::Relaxed);
+            match self.available.select(current) {
+                Some(id) => Some(id),
+                None => {
+                    self.look_into_bitmap.store(false, Ordering::Relaxed);
+                    Some(self.current.fetch_add(1, Ordering::Relaxed))
+                }
+            }
+        } else {
+            Some(self.current.fetch_add(1, Ordering::Relaxed))
+        }
+    }
+
+    /// Returns the number of used ids in total.
+    pub fn used(&self) -> u64 {
+        self.used.load(Ordering::Relaxed)
+    }
+}

milli/src/update/index_documents/transform.rs

@@ -27,7 +27,7 @@ use crate::update::del_add::{
 };
 use crate::update::index_documents::GrenadParameters;
 use crate::update::settings::{InnerIndexSettings, InnerIndexSettingsDiff};
-use crate::update::{AvailableDocumentsIds, UpdateIndexingStep};
+use crate::update::{AvailableIds, UpdateIndexingStep};
 use crate::vector::parsed_vectors::{ExplicitVectors, VectorOrArrayOfVectors};
 use crate::vector::settings::{EmbedderAction, WriteBackToDocuments};
 use crate::{
@@ -55,7 +55,7 @@ pub struct Transform<'a, 'i> {
 
     indexer_settings: &'a IndexerConfig,
     pub index_documents_method: IndexDocumentsMethod,
-    available_documents_ids: AvailableDocumentsIds,
+    available_documents_ids: AvailableIds,
 
     // Both grenad follows the same format:
     // key | value
@@ -143,7 +143,7 @@ impl<'a, 'i> Transform<'a, 'i> {
             index,
             fields_ids_map: index.fields_ids_map(wtxn)?,
             indexer_settings,
-            available_documents_ids: AvailableDocumentsIds::from_documents_ids(&documents_ids),
+            available_documents_ids: AvailableIds::new(&documents_ids),
             original_sorter,
             flattened_sorter,
             index_documents_method,

milli/src/update/mod.rs

@@ -1,5 +1,6 @@
-pub use self::available_documents_ids::AvailableDocumentsIds;
+pub use self::available_ids::AvailableIds;
 pub use self::clear_documents::ClearDocuments;
+pub use self::concurrent_available_ids::ConcurrentAvailableIds;
 pub use self::facet::bulk::FacetsUpdateBulk;
 pub use self::facet::incremental::FacetsUpdateIncrementalInner;
 pub use self::index_documents::*;
@@ -10,8 +11,9 @@ pub use self::word_prefix_docids::WordPrefixDocids;
 pub use self::words_prefix_integer_docids::WordPrefixIntegerDocids;
 pub use self::words_prefixes_fst::WordsPrefixesFst;
 
-mod available_documents_ids;
+mod available_ids;
 mod clear_documents;
+mod concurrent_available_ids;
 pub(crate) mod del_add;
 pub(crate) mod facet;
 mod index_documents;