Implementing an IS EMPTY filter

filter-parser/src/condition.rs

@@ -21,6 +21,7 @@ pub enum Condition<'a> {
     Equal(Token<'a>),
     NotEqual(Token<'a>),
     Null,
+    Empty,
     Exists,
     LowerThan(Token<'a>),
     LowerThanOrEqual(Token<'a>),
@@ -61,6 +62,22 @@ pub fn parse_is_not_null(input: Span) -> IResult<FilterCondition> {
     Ok((input, FilterCondition::Not(Box::new(FilterCondition::Condition { fid: key, op: Null }))))
 }
 
+/// empty          = value "IS" WS+ "EMPTY"
+pub fn parse_is_empty(input: Span) -> IResult<FilterCondition> {
+    let (input, key) = parse_value(input)?;
+
+    let (input, _) = tuple((tag("IS"), multispace1, tag("EMPTY")))(input)?;
+    Ok((input, FilterCondition::Condition { fid: key, op: Empty }))
+}
+
+/// empty          = value "IS" WS+ "NOT" WS+ "EMPTY"
+pub fn parse_is_not_empty(input: Span) -> IResult<FilterCondition> {
+    let (input, key) = parse_value(input)?;
+
+    let (input, _) = tuple((tag("IS"), multispace1, tag("NOT"), multispace1, tag("EMPTY")))(input)?;
+    Ok((input, FilterCondition::Not(Box::new(FilterCondition::Condition { fid: key, op: Empty }))))
+}
+
 /// exist          = value "EXISTS"
 pub fn parse_exists(input: Span) -> IResult<FilterCondition> {
     let (input, key) = terminated(parse_value, tag("EXISTS"))(input)?;

filter-parser/src/error.rs

@@ -143,11 +143,9 @@ impl<'a> Display for Error<'a> {
             ErrorKind::MissingClosingDelimiter(c) => {
                 writeln!(f, "Expression `{}` is missing the following closing delimiter: `{}`.", escaped_input, c)?
             }
-            ErrorKind::InvalidPrimary if input.trim().is_empty() => {
-                writeln!(f, "Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `_geoRadius`, or `_geoBoundingBox` but instead got nothing.")?
-            }
             ErrorKind::InvalidPrimary => {
-                writeln!(f, "Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `_geoRadius`, or `_geoBoundingBox` at `{}`.", escaped_input)?
+                let text = if input.trim().is_empty() { "but instead got nothing.".to_string() } else { format!("at `{}`.", escaped_input) };
+                writeln!(f, "Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `IS EMPTY`, `IS NOT EMPTY`, `_geoRadius`, or `_geoBoundingBox` {}", text)?
             }
             ErrorKind::ExpectedEof => {
                 writeln!(f, "Found unexpected characters at the end of the filter: `{}`. You probably forgot an `OR` or an `AND` rule.", escaped_input)?

filter-parser/src/lib.rs

@@ -47,7 +47,10 @@ mod value;
 use std::fmt::Debug;
 
 pub use condition::{parse_condition, parse_to, Condition};
-use condition::{parse_exists, parse_is_not_null, parse_is_null, parse_not_exists};
+use condition::{
+    parse_exists, parse_is_empty, parse_is_not_empty, parse_is_not_null, parse_is_null,
+    parse_not_exists,
+};
 use error::{cut_with_err, ExpectedValueKind, NomErrorExt};
 pub use error::{Error, ErrorKind};
 use nom::branch::alt;
@@ -416,6 +419,8 @@ fn parse_primary(input: Span, depth: usize) -> IResult<FilterCondition> {
         parse_condition,
         parse_is_null,
         parse_is_not_null,
+        parse_is_empty,
+        parse_is_not_empty,
         parse_exists,
         parse_not_exists,
         parse_to,
@@ -509,6 +514,13 @@ pub mod tests {
         insta::assert_display_snapshot!(p("NOT subscribers IS NOT NULL"), @"{subscribers} IS NULL");
         insta::assert_display_snapshot!(p("subscribers  IS   NOT   NULL"), @"NOT ({subscribers} IS NULL)");
 
+        // Test EMPTY + NOT EMPTY
+        insta::assert_display_snapshot!(p("subscribers IS EMPTY"), @"{subscribers} IS EMPTY");
+        insta::assert_display_snapshot!(p("NOT subscribers IS EMPTY"), @"NOT ({subscribers} IS EMPTY)");
+        insta::assert_display_snapshot!(p("subscribers IS NOT EMPTY"), @"NOT ({subscribers} IS EMPTY)");
+        insta::assert_display_snapshot!(p("NOT subscribers IS NOT EMPTY"), @"{subscribers} IS EMPTY");
+        insta::assert_display_snapshot!(p("subscribers  IS   NOT   EMPTY"), @"NOT ({subscribers} IS EMPTY)");
+
         // Test EXISTS + NOT EXITS
         insta::assert_display_snapshot!(p("subscribers EXISTS"), @"{subscribers} EXISTS");
         insta::assert_display_snapshot!(p("NOT subscribers EXISTS"), @"NOT ({subscribers} EXISTS)");
@@ -587,7 +599,7 @@ pub mod tests {
         "###);
 
         insta::assert_display_snapshot!(p("'OR'"), @r###"
-        Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `_geoRadius`, or `_geoBoundingBox` at `\'OR\'`.
+        Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `IS EMPTY`, `IS NOT EMPTY`, `_geoRadius`, or `_geoBoundingBox` at `\'OR\'`.
         1:5 'OR'
         "###);
 
@@ -597,12 +609,12 @@ pub mod tests {
         "###);
 
         insta::assert_display_snapshot!(p("channel Ponce"), @r###"
-        Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `_geoRadius`, or `_geoBoundingBox` at `channel Ponce`.
+        Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `IS EMPTY`, `IS NOT EMPTY`, `_geoRadius`, or `_geoBoundingBox` at `channel Ponce`.
         1:14 channel Ponce
         "###);
 
         insta::assert_display_snapshot!(p("channel = Ponce OR"), @r###"
-        Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `_geoRadius`, or `_geoBoundingBox` but instead got nothing.
+        Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `IS EMPTY`, `IS NOT EMPTY`, `_geoRadius`, or `_geoBoundingBox` but instead got nothing.
         19:19 channel = Ponce OR
         "###);
 
@@ -667,12 +679,12 @@ pub mod tests {
         "###);
 
         insta::assert_display_snapshot!(p("colour NOT EXIST"), @r###"
-        Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `_geoRadius`, or `_geoBoundingBox` at `colour NOT EXIST`.
+        Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `IS EMPTY`, `IS NOT EMPTY`, `_geoRadius`, or `_geoBoundingBox` at `colour NOT EXIST`.
         1:17 colour NOT EXIST
         "###);
 
         insta::assert_display_snapshot!(p("subscribers 100 TO1000"), @r###"
-        Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `_geoRadius`, or `_geoBoundingBox` at `subscribers 100 TO1000`.
+        Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `IS EMPTY`, `IS NOT EMPTY`, `_geoRadius`, or `_geoBoundingBox` at `subscribers 100 TO1000`.
         1:23 subscribers 100 TO1000
         "###);
 
@@ -812,6 +824,7 @@ impl<'a> std::fmt::Display for Condition<'a> {
             Condition::Equal(token) => write!(f, "= {token}"),
             Condition::NotEqual(token) => write!(f, "!= {token}"),
             Condition::Null => write!(f, "IS NULL"),
+            Condition::Empty => write!(f, "IS EMPTY"),
             Condition::Exists => write!(f, "EXISTS"),
             Condition::LowerThan(token) => write!(f, "< {token}"),
             Condition::LowerThanOrEqual(token) => write!(f, "<= {token}"),

filter-parser/src/value.rs

@@ -188,6 +188,7 @@ fn is_keyword(s: &str) -> bool {
             | "EXISTS"
             | "IS"
             | "NULL"
+            | "EMPTY"
             | "_geoRadius"
             | "_geoBoundingBox"
     )

meilisearch/tests/search/errors.rs

@@ -547,7 +547,7 @@ async fn filter_invalid_syntax_object() {
     index.wait_task(1).await;
 
     let expected_response = json!({
-        "message": "Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `_geoRadius`, or `_geoBoundingBox` at `title & Glass`.\n1:14 title & Glass",
+        "message": "Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `IS EMPTY`, `IS NOT EMPTY`, `_geoRadius`, or `_geoBoundingBox` at `title & Glass`.\n1:14 title & Glass",
         "code": "invalid_search_filter",
         "type": "invalid_request",
         "link": "https://docs.meilisearch.com/errors#invalid_search_filter"
@@ -572,7 +572,7 @@ async fn filter_invalid_syntax_array() {
     index.wait_task(1).await;
 
     let expected_response = json!({
-        "message": "Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `_geoRadius`, or `_geoBoundingBox` at `title & Glass`.\n1:14 title & Glass",
+        "message": "Was expecting an operation `=`, `!=`, `>=`, `>`, `<=`, `<`, `IN`, `NOT IN`, `TO`, `EXISTS`, `NOT EXISTS`, `IS NULL`, `IS NOT NULL`, `IS EMPTY`, `IS NOT EMPTY`, `_geoRadius`, or `_geoBoundingBox` at `title & Glass`.\n1:14 title & Glass",
         "code": "invalid_search_filter",
         "type": "invalid_request",
         "link": "https://docs.meilisearch.com/errors#invalid_search_filter"

milli/src/index.rs

@@ -81,6 +81,7 @@ pub mod db_name {
     pub const FACET_ID_F64_DOCIDS: &str = "facet-id-f64-docids";
     pub const FACET_ID_EXISTS_DOCIDS: &str = "facet-id-exists-docids";
     pub const FACET_ID_IS_NULL_DOCIDS: &str = "facet-id-is-null-docids";
+    pub const FACET_ID_IS_EMPTY_DOCIDS: &str = "facet-id-is-empty-docids";
     pub const FACET_ID_STRING_DOCIDS: &str = "facet-id-string-docids";
     pub const FIELD_ID_DOCID_FACET_F64S: &str = "field-id-docid-facet-f64s";
     pub const FIELD_ID_DOCID_FACET_STRINGS: &str = "field-id-docid-facet-strings";
@@ -130,9 +131,10 @@ pub struct Index {
 
     /// Maps the facet field id and the docids for which this field exists
     pub facet_id_exists_docids: Database<FieldIdCodec, CboRoaringBitmapCodec>,
-
     /// Maps the facet field id and the docids for which this field is set as null
     pub facet_id_is_null_docids: Database<FieldIdCodec, CboRoaringBitmapCodec>,
+    /// Maps the facet field id and the docids for which this field is considered empty
+    pub facet_id_is_empty_docids: Database<FieldIdCodec, CboRoaringBitmapCodec>,
 
     /// Maps the facet field id and ranges of numbers with the docids that corresponds to them.
     pub facet_id_f64_docids: Database<FacetGroupKeyCodec<OrderedF64Codec>, FacetGroupValueCodec>,
@@ -157,7 +159,7 @@ impl Index {
     ) -> Result<Index> {
         use db_name::*;
 
-        options.max_dbs(20);
+        options.max_dbs(21);
         unsafe { options.flag(Flags::MdbAlwaysFreePages) };
 
         let env = options.open(path)?;
@@ -180,6 +182,7 @@ impl Index {
         let facet_id_string_docids = env.create_database(Some(FACET_ID_STRING_DOCIDS))?;
         let facet_id_exists_docids = env.create_database(Some(FACET_ID_EXISTS_DOCIDS))?;
         let facet_id_is_null_docids = env.create_database(Some(FACET_ID_IS_NULL_DOCIDS))?;
+        let facet_id_is_empty_docids = env.create_database(Some(FACET_ID_IS_EMPTY_DOCIDS))?;
 
         let field_id_docid_facet_f64s = env.create_database(Some(FIELD_ID_DOCID_FACET_F64S))?;
         let field_id_docid_facet_strings =
@@ -207,6 +210,7 @@ impl Index {
             facet_id_string_docids,
             facet_id_exists_docids,
             facet_id_is_null_docids,
+            facet_id_is_empty_docids,
             field_id_docid_facet_f64s,
             field_id_docid_facet_strings,
             documents,
@@ -851,6 +855,18 @@ impl Index {
         }
     }
 
+    /// Retrieve all the documents which contain this field id and that is considered empty
+    pub fn empty_faceted_documents_ids(
+        &self,
+        rtxn: &RoTxn,
+        field_id: FieldId,
+    ) -> heed::Result<RoaringBitmap> {
+        match self.facet_id_is_empty_docids.get(rtxn, &BEU16::new(field_id))? {
+            Some(docids) => Ok(docids),
+            None => Ok(RoaringBitmap::new()),
+        }
+    }
+
     /// Retrieve all the documents which contain this field id
     pub fn exists_faceted_documents_ids(
         &self,

milli/src/search/facet/filter.rs

@@ -223,6 +223,10 @@ impl<'a> Filter<'a> {
                 let is_null = index.null_faceted_documents_ids(rtxn, field_id)?;
                 return Ok(is_null);
             }
+            Condition::Empty => {
+                let is_empty = index.empty_faceted_documents_ids(rtxn, field_id)?;
+                return Ok(is_empty);
+            }
             Condition::Exists => {
                 let exist = index.exists_faceted_documents_ids(rtxn, field_id)?;
                 return Ok(exist);

milli/src/update/clear_documents.rs

@@ -35,6 +35,7 @@ impl<'t, 'u, 'i> ClearDocuments<'t, 'u, 'i> {
             facet_id_string_docids,
             facet_id_exists_docids,
             facet_id_is_null_docids,
+            facet_id_is_empty_docids,
             field_id_docid_facet_f64s,
             field_id_docid_facet_strings,
             documents,
@@ -88,6 +89,7 @@ impl<'t, 'u, 'i> ClearDocuments<'t, 'u, 'i> {
         facet_id_f64_docids.clear(self.wtxn)?;
         facet_id_exists_docids.clear(self.wtxn)?;
         facet_id_is_null_docids.clear(self.wtxn)?;
+        facet_id_is_empty_docids.clear(self.wtxn)?;
         facet_id_string_docids.clear(self.wtxn)?;
         field_id_docid_facet_f64s.clear(self.wtxn)?;
         field_id_docid_facet_strings.clear(self.wtxn)?;

milli/src/update/delete_documents.rs

@@ -246,6 +246,7 @@ impl<'t, 'u, 'i> DeleteDocuments<'t, 'u, 'i> {
             script_language_docids,
             facet_id_exists_docids,
             facet_id_is_null_docids,
+            facet_id_is_empty_docids,
             documents,
         } = self.index;
 
@@ -531,6 +532,13 @@ impl<'t, 'u, 'i> DeleteDocuments<'t, 'u, 'i> {
             &self.to_delete_docids,
         )?;
 
+        // We delete the documents ids that are under the facet field id values.
+        remove_docids_from_facet_id_docids(
+            self.wtxn,
+            facet_id_is_empty_docids,
+            &self.to_delete_docids,
+        )?;
+
         self.index.put_soft_deleted_documents_ids(self.wtxn, &RoaringBitmap::new())?;
 
         Ok(DetailedDocumentDeletionResult {

milli/src/update/index_documents/extract/extract_fid_docid_facet_values.rs

@@ -21,6 +21,7 @@ pub struct ExtractedFacetValues {
     pub docid_fid_facet_numbers_chunk: grenad::Reader<File>,
     pub docid_fid_facet_strings_chunk: grenad::Reader<File>,
     pub fid_facet_is_null_docids_chunk: grenad::Reader<File>,
+    pub fid_facet_is_empty_docids_chunk: grenad::Reader<File>,
     pub fid_facet_exists_docids_chunk: grenad::Reader<File>,
 }
 
@@ -56,6 +57,7 @@ pub fn extract_fid_docid_facet_values<R: io::Read + io::Seek>(
 
     let mut facet_exists_docids = BTreeMap::<FieldId, RoaringBitmap>::new();
     let mut facet_is_null_docids = BTreeMap::<FieldId, RoaringBitmap>::new();
+    let mut facet_is_empty_docids = BTreeMap::<FieldId, RoaringBitmap>::new();
 
     let mut key_buffer = Vec::new();
     let mut cursor = obkv_documents.into_cursor()?;
@@ -80,10 +82,14 @@ pub fn extract_fid_docid_facet_values<R: io::Read + io::Seek>(
                 key_buffer.extend_from_slice(docid_bytes);
 
                 let value = from_slice(field_bytes).map_err(InternalError::SerdeJson)?;
+
                 match extract_facet_values(&value) {
                     FilterableValues::Null => {
                         facet_is_null_docids.entry(field_id).or_default().insert(document);
                     }
+                    FilterableValues::Empty => {
+                        facet_is_empty_docids.entry(field_id).or_default().insert(document);
+                    }
                     FilterableValues::Values { numbers, strings } => {
                         // insert facet numbers in sorter
                         for number in numbers {
@@ -140,22 +146,34 @@ pub fn extract_fid_docid_facet_values<R: io::Read + io::Seek>(
     }
     let facet_is_null_docids_reader = writer_into_reader(facet_is_null_docids_writer)?;
 
+    let mut facet_is_empty_docids_writer = create_writer(
+        indexer.chunk_compression_type,
+        indexer.chunk_compression_level,
+        tempfile::tempfile()?,
+    );
+    for (fid, bitmap) in facet_is_empty_docids.into_iter() {
+        let bitmap_bytes = CboRoaringBitmapCodec::bytes_encode(&bitmap).unwrap();
+        facet_is_empty_docids_writer.insert(fid.to_be_bytes(), &bitmap_bytes)?;
+    }
+    let facet_is_empty_docids_reader = writer_into_reader(facet_is_empty_docids_writer)?;
+
     Ok(ExtractedFacetValues {
         docid_fid_facet_numbers_chunk: sorter_into_reader(fid_docid_facet_numbers_sorter, indexer)?,
         docid_fid_facet_strings_chunk: sorter_into_reader(fid_docid_facet_strings_sorter, indexer)?,
         fid_facet_is_null_docids_chunk: facet_is_null_docids_reader,
+        fid_facet_is_empty_docids_chunk: facet_is_empty_docids_reader,
         fid_facet_exists_docids_chunk: facet_exists_docids_reader,
     })
 }
 
 /// Represent what a document field contains.
 enum FilterableValues {
+    /// Corresponds to the JSON `null` value.
     Null,
+    /// Corresponds to either, an empty string `""`, an empty array `[]`, or an empty object `{}`.
+    Empty,
     /// Represents all the numbers and strings values found in this document field.
-    Values {
+    Values { numbers: Vec<f64>, strings: Vec<(String, String)> },
-        numbers: Vec<f64>,
-        strings: Vec<(String, String)>,
-    },
 }
 
 fn extract_facet_values(value: &Value) -> FilterableValues {
@@ -192,6 +210,9 @@ fn extract_facet_values(value: &Value) -> FilterableValues {
 
     match value {
         Value::Null => FilterableValues::Null,
+        Value::String(s) if s.is_empty() => FilterableValues::Empty,
+        Value::Array(a) if a.is_empty() => FilterableValues::Empty,
+        Value::Object(o) if o.is_empty() => FilterableValues::Empty,
         otherwise => {
             let mut numbers = Vec::new();
             let mut strings = Vec::new();

milli/src/update/index_documents/extract/mod.rs

@@ -55,22 +55,23 @@ pub(crate) fn data_from_obkv_documents(
         .collect::<Result<()>>()?;
 
     #[allow(clippy::type_complexity)]
-    let result: Result<(Vec<_>, (Vec<_>, (Vec<_>, (Vec<_>, Vec<_>))))> = flattened_obkv_chunks
+    let result: Result<(Vec<_>, (Vec<_>, (Vec<_>, (Vec<_>, (Vec<_>, Vec<_>)))))> =
-        .par_bridge()
+        flattened_obkv_chunks
-        .map(|flattened_obkv_chunks| {
+            .par_bridge()
-            send_and_extract_flattened_documents_data(
+            .map(|flattened_obkv_chunks| {
-                flattened_obkv_chunks,
+                send_and_extract_flattened_documents_data(
-                indexer,
+                    flattened_obkv_chunks,
-                lmdb_writer_sx.clone(),
+                    indexer,
-                &searchable_fields,
+                    lmdb_writer_sx.clone(),
-                &faceted_fields,
+                    &searchable_fields,
-                primary_key_id,
+                    &faceted_fields,
-                geo_fields_ids,
+                    primary_key_id,
-                &stop_words,
+                    geo_fields_ids,
-                max_positions_per_attributes,
+                    &stop_words,
-            )
+                    max_positions_per_attributes,
-        })
+                )
-        .collect();
+            })
+            .collect();
 
     let (
         docid_word_positions_chunks,
@@ -78,7 +79,10 @@ pub(crate) fn data_from_obkv_documents(
             docid_fid_facet_numbers_chunks,
             (
                 docid_fid_facet_strings_chunks,
-                (facet_is_null_docids_chunks, facet_exists_docids_chunks),
+                (
+                    facet_is_null_docids_chunks,
+                    (facet_is_empty_docids_chunks, facet_exists_docids_chunks),
+                ),
             ),
         ),
     ) = result?;
@@ -115,6 +119,22 @@ pub(crate) fn data_from_obkv_documents(
         });
     }
 
+    // merge facet_is_empty_docids and send them as a typed chunk
+    {
+        let lmdb_writer_sx = lmdb_writer_sx.clone();
+        rayon::spawn(move || {
+            debug!("merge {} database", "facet-id-is-empty-docids");
+            match facet_is_empty_docids_chunks.merge(merge_cbo_roaring_bitmaps, &indexer) {
+                Ok(reader) => {
+                    let _ = lmdb_writer_sx.send(Ok(TypedChunk::FieldIdFacetIsEmptyDocids(reader)));
+                }
+                Err(e) => {
+                    let _ = lmdb_writer_sx.send(Err(e));
+                }
+            }
+        });
+    }
+
     spawn_extraction_task::<_, _, Vec<grenad::Reader<File>>>(
         docid_word_positions_chunks.clone(),
         indexer,
@@ -254,7 +274,10 @@ fn send_and_extract_flattened_documents_data(
     grenad::Reader<CursorClonableMmap>,
     (
         grenad::Reader<CursorClonableMmap>,
-        (grenad::Reader<CursorClonableMmap>, (grenad::Reader<File>, grenad::Reader<File>)),
+        (
+            grenad::Reader<CursorClonableMmap>,
+            (grenad::Reader<File>, (grenad::Reader<File>, grenad::Reader<File>)),
+        ),
     ),
 )> {
     let flattened_documents_chunk =
@@ -304,6 +327,7 @@ fn send_and_extract_flattened_documents_data(
                     docid_fid_facet_numbers_chunk,
                     docid_fid_facet_strings_chunk,
                     fid_facet_is_null_docids_chunk,
+                    fid_facet_is_empty_docids_chunk,
                     fid_facet_exists_docids_chunk,
                 } = extract_fid_docid_facet_values(
                     flattened_documents_chunk.clone(),
@@ -331,7 +355,10 @@ fn send_and_extract_flattened_documents_data(
                     docid_fid_facet_numbers_chunk,
                     (
                         docid_fid_facet_strings_chunk,
-                        (fid_facet_is_null_docids_chunk, fid_facet_exists_docids_chunk),
+                        (
+                            fid_facet_is_null_docids_chunk,
+                            (fid_facet_is_empty_docids_chunk, fid_facet_exists_docids_chunk),
+                        ),
                     ),
                 ))
             },

milli/src/update/index_documents/typed_chunk.rs

@@ -40,6 +40,7 @@ pub(crate) enum TypedChunk {
     FieldIdFacetNumberDocids(grenad::Reader<File>),
     FieldIdFacetExistsDocids(grenad::Reader<File>),
     FieldIdFacetIsNullDocids(grenad::Reader<File>),
+    FieldIdFacetIsEmptyDocids(grenad::Reader<File>),
     GeoPoints(grenad::Reader<File>),
     ScriptLanguageDocids(HashMap<(Script, Language), RoaringBitmap>),
 }
@@ -173,6 +174,17 @@ pub(crate) fn write_typed_chunk_into_index(
             )?;
             is_merged_database = true;
         }
+        TypedChunk::FieldIdFacetIsEmptyDocids(facet_id_is_empty_docids) => {
+            append_entries_into_database(
+                facet_id_is_empty_docids,
+                &index.facet_id_is_empty_docids,
+                wtxn,
+                index_is_empty,
+                |value, _buffer| Ok(value),
+                merge_cbo_roaring_bitmaps,
+            )?;
+            is_merged_database = true;
+        }
         TypedChunk::WordPairProximityDocids(word_pair_proximity_docids_iter) => {
             append_entries_into_database(
                 word_pair_proximity_docids_iter,