diff --git a/src/heed_codec/facet/facet_value_f64_codec.rs b/src/heed_codec/facet/facet_value_f64_codec.rs
index fdacb1f08..228514de5 100644
--- a/src/heed_codec/facet/facet_value_f64_codec.rs
+++ b/src/heed_codec/facet/facet_value_f64_codec.rs
@@ -1,26 +1,24 @@
 use std::borrow::Cow;
 use std::convert::TryInto;
-use std::str;
 
-use crate::heed_codec::StrBytesCodec;
 use crate::facet::value_encoding::f64_into_bytes;
 
 pub struct FacetValueF64Codec;
 
 impl<'a> heed::BytesDecode<'a> for FacetValueF64Codec {
-    type DItem = (&'a str, f64);
+    type DItem = (u8, f64);
 
     fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let (name, buffer) = StrBytesCodec::bytes_decode(bytes)?;
+        let (field_id, buffer) = bytes.split_first()?;
         let value = buffer[8..].try_into().ok().map(f64::from_be_bytes)?;
-        Some((name, value))
+        Some((*field_id, value))
     }
 }
 
-impl<'a> heed::BytesEncode<'a> for FacetValueF64Codec {
-    type EItem = (&'a str, f64);
+impl heed::BytesEncode<'_> for FacetValueF64Codec {
+    type EItem = (u8, f64);
 
-    fn bytes_encode((name, value): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((field_id, value): &Self::EItem) -> Option<Cow<[u8]>> {
         let mut buffer = [0u8; 16];
 
         // Write the globally ordered float.
@@ -31,8 +29,10 @@ impl<'a> heed::BytesEncode<'a> for FacetValueF64Codec {
         let bytes = value.to_be_bytes();
         buffer[8..].copy_from_slice(&bytes[..]);
 
-        let tuple = (*name, &buffer[..]);
-        StrBytesCodec::bytes_encode(&tuple).map(Cow::into_owned).map(Cow::Owned)
+        let mut bytes = Vec::with_capacity(buffer.len() + 1);
+        bytes.push(*field_id);
+        bytes.extend_from_slice(&buffer[..]);
+        Some(Cow::Owned(bytes))
     }
 }
 
@@ -43,8 +43,8 @@ mod tests {
 
     #[test]
     fn globally_ordered_f64() {
-        let bytes = FacetValueF64Codec::bytes_encode(&("hello", -32.0)).unwrap();
+        let bytes = FacetValueF64Codec::bytes_encode(&(3, -32.0)).unwrap();
         let (name, value) = FacetValueF64Codec::bytes_decode(&bytes).unwrap();
-        assert_eq!((name, value), ("hello", -32.0));
+        assert_eq!((name, value), (3, -32.0));
     }
 }
diff --git a/src/heed_codec/facet/facet_value_i64_codec.rs b/src/heed_codec/facet/facet_value_i64_codec.rs
index e3c333883..f99b8a3ea 100644
--- a/src/heed_codec/facet/facet_value_i64_codec.rs
+++ b/src/heed_codec/facet/facet_value_i64_codec.rs
@@ -1,28 +1,28 @@
 use std::borrow::Cow;
 use std::convert::TryInto;
-use std::str;
 
-use crate::heed_codec::StrBytesCodec;
 use crate::facet::value_encoding::{i64_from_bytes, i64_into_bytes};
 
 pub struct FacetValueI64Codec;
 
 impl<'a> heed::BytesDecode<'a> for FacetValueI64Codec {
-    type DItem = (&'a str, i64);
+    type DItem = (u8, i64);
 
     fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let (name, bytes) = StrBytesCodec::bytes_decode(bytes)?;
-        let value = bytes.try_into().map(i64_from_bytes).ok()?;
-        Some((name, value))
+        let (field_id, buffer) = bytes.split_first()?;
+        let value = buffer.try_into().map(i64_from_bytes).ok()?;
+        Some((*field_id, value))
     }
 }
 
-impl<'a> heed::BytesEncode<'a> for FacetValueI64Codec {
-    type EItem = (&'a str, i64);
+impl heed::BytesEncode<'_> for FacetValueI64Codec {
+    type EItem = (u8, i64);
 
-    fn bytes_encode((name, value): &Self::EItem) -> Option<Cow<[u8]>> {
+    fn bytes_encode((field_id, value): &Self::EItem) -> Option<Cow<[u8]>> {
         let value = i64_into_bytes(*value);
-        let tuple = (*name, &value[..]);
-        StrBytesCodec::bytes_encode(&tuple).map(Cow::into_owned).map(Cow::Owned)
+        let mut bytes = Vec::with_capacity(value.len() + 1);
+        bytes.push(*field_id);
+        bytes.extend_from_slice(&value[..]);
+        Some(Cow::Owned(bytes))
     }
 }
diff --git a/src/heed_codec/facet/facet_value_string_codec.rs b/src/heed_codec/facet/facet_value_string_codec.rs
index 8b046192a..faa8b407b 100644
--- a/src/heed_codec/facet/facet_value_string_codec.rs
+++ b/src/heed_codec/facet/facet_value_string_codec.rs
@@ -1,25 +1,25 @@
 use std::borrow::Cow;
 use std::str;
 
-use crate::heed_codec::StrBytesCodec;
-
 pub struct FacetValueStringCodec;
 
 impl<'a> heed::BytesDecode<'a> for FacetValueStringCodec {
-    type DItem = (&'a str, &'a str);
+    type DItem = (u8, &'a str);
 
     fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let (name, bytes) = StrBytesCodec::bytes_decode(bytes)?;
+        let (field_id, bytes) = bytes.split_first()?;
         let value = str::from_utf8(bytes).ok()?;
-        Some((name, value))
+        Some((*field_id, value))
     }
 }
 
 impl<'a> heed::BytesEncode<'a> for FacetValueStringCodec {
-    type EItem = (&'a str, &'a str);
+    type EItem = (u8, &'a str);
 
-    fn bytes_encode((name, value): &Self::EItem) -> Option<Cow<[u8]>> {
-        let tuple = (*name, value.as_bytes());
-        StrBytesCodec::bytes_encode(&tuple).map(Cow::into_owned).map(Cow::Owned)
+    fn bytes_encode((field_id, value): &Self::EItem) -> Option<Cow<[u8]>> {
+        let mut bytes = Vec::with_capacity(value.len() + 1);
+        bytes.push(*field_id);
+        bytes.extend_from_slice(value.as_bytes());
+        Some(Cow::Owned(bytes))
     }
 }
diff --git a/src/heed_codec/mod.rs b/src/heed_codec/mod.rs
index 260e79c4b..e7b8cf256 100644
--- a/src/heed_codec/mod.rs
+++ b/src/heed_codec/mod.rs
@@ -1,16 +1,14 @@
 mod beu32_str_codec;
 mod bo_roaring_bitmap_codec;
 mod cbo_roaring_bitmap_codec;
-mod facet;
 mod obkv_codec;
 mod roaring_bitmap_codec;
-mod str_bytes_codec;
 mod str_str_u8_codec;
+pub mod facet;
 
 pub use self::beu32_str_codec::BEU32StrCodec;
 pub use self::bo_roaring_bitmap_codec::BoRoaringBitmapCodec;
 pub use self::cbo_roaring_bitmap_codec::CboRoaringBitmapCodec;
 pub use self::obkv_codec::ObkvCodec;
 pub use self::roaring_bitmap_codec::RoaringBitmapCodec;
-pub use self::str_bytes_codec::StrBytesCodec;
 pub use self::str_str_u8_codec::StrStrU8Codec;
diff --git a/src/heed_codec/str_bytes_codec.rs b/src/heed_codec/str_bytes_codec.rs
deleted file mode 100644
index 1a864c1fb..000000000
--- a/src/heed_codec/str_bytes_codec.rs
+++ /dev/null
@@ -1,28 +0,0 @@
-use std::borrow::Cow;
-use std::str;
-
-pub struct StrBytesCodec;
-
-impl<'a> heed::BytesDecode<'a> for StrBytesCodec {
-    type DItem = (&'a str, &'a [u8]);
-
-    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
-        let s1_end = bytes.iter().position(|b| *b == 0)?;
-        let (s1_bytes, s2_bytes) = bytes.split_at(s1_end);
-        let s1 = str::from_utf8(s1_bytes).ok()?;
-        let s2 = &s2_bytes[1..];
-        Some((s1, s2))
-    }
-}
-
-impl<'a> heed::BytesEncode<'a> for StrBytesCodec {
-    type EItem = (&'a str, &'a [u8]);
-
-    fn bytes_encode((s1, s2): &Self::EItem) -> Option<Cow<[u8]>> {
-        let mut bytes = Vec::with_capacity(s1.len() + s2.len() + 1);
-        bytes.extend_from_slice(s1.as_bytes());
-        bytes.push(0);
-        bytes.extend_from_slice(s2);
-        Some(Cow::Owned(bytes))
-    }
-}