feat: support to sepcify ef search param (#1844)

Signed-off-by: BubbleCal <bubble-cal@outlook.com>

nodejs/__test__/table.test.ts

@@ -477,6 +477,54 @@ describe("When creating an index", () => {
     expect(rst.numRows).toBe(1);
   });
 
+  it("should create and search IVF_HNSW indices", async () => {
+    await tbl.createIndex("vec", {
+      config: Index.hnswSq(),
+    });
+
+    // check index directory
+    const indexDir = path.join(tmpDir.name, "test.lance", "_indices");
+    expect(fs.readdirSync(indexDir)).toHaveLength(1);
+    const indices = await tbl.listIndices();
+    expect(indices.length).toBe(1);
+    expect(indices[0]).toEqual({
+      name: "vec_idx",
+      indexType: "IvfHnswSq",
+      columns: ["vec"],
+    });
+
+    // Search without specifying the column
+    let rst = await tbl
+      .query()
+      .limit(2)
+      .nearestTo(queryVec)
+      .distanceType("dot")
+      .toArrow();
+    expect(rst.numRows).toBe(2);
+
+    // Search using `vectorSearch`
+    rst = await tbl.vectorSearch(queryVec).limit(2).toArrow();
+    expect(rst.numRows).toBe(2);
+
+    // Search with specifying the column
+    const rst2 = await tbl
+      .query()
+      .limit(2)
+      .nearestTo(queryVec)
+      .column("vec")
+      .toArrow();
+    expect(rst2.numRows).toBe(2);
+    expect(rst.toString()).toEqual(rst2.toString());
+
+    // test offset
+    rst = await tbl.query().limit(2).offset(1).nearestTo(queryVec).toArrow();
+    expect(rst.numRows).toBe(1);
+
+    // test ef
+    rst = await tbl.query().limit(2).nearestTo(queryVec).ef(100).toArrow();
+    expect(rst.numRows).toBe(2);
+  });
+
   it("should be able to query unindexed data", async () => {
     await tbl.createIndex("vec");
     await tbl.add([

nodejs/lancedb/query.ts

@@ -385,6 +385,20 @@ export class VectorQuery extends QueryBase<NativeVectorQuery> {
     return this;
   }
 
+  /**
+   * Set the number of candidates to consider during the search
+   *
+   * This argument is only used when the vector column has an HNSW index.
+   * If there is no index then this value is ignored.
+   *
+   * Increasing this value will increase the recall of your query but will
+   * also increase the latency of your query. The default value is 1.5*limit.
+   */
+  ef(ef: number): VectorQuery {
+    super.doCall((inner) => inner.ef(ef));
+    return this;
+  }
+
   /**
    * Set the vector column to query
    *

nodejs/src/query.rs

@@ -167,6 +167,11 @@ impl VectorQuery {
         self.inner = self.inner.clone().nprobes(nprobe as usize);
     }
 
+    #[napi]
+    pub fn ef(&mut self, ef: u32) {
+        self.inner = self.inner.clone().ef(ef as usize);
+    }
+
     #[napi]
     pub fn bypass_vector_index(&mut self) {
         self.inner = self.inner.clone().bypass_vector_index()

python/python/lancedb/query.py

@@ -131,6 +131,8 @@ class Query(pydantic.BaseModel):
 
     fast_search: bool = False
 
+    ef: Optional[int] = None
+
 
 class LanceQueryBuilder(ABC):
     """An abstract query builder. Subclasses are defined for vector search,
@@ -257,6 +259,7 @@ class LanceQueryBuilder(ABC):
         self._with_row_id = False
         self._vector = None
         self._text = None
+        self._ef = None
 
     @deprecation.deprecated(
         deprecated_in="0.3.1",
@@ -638,6 +641,28 @@ class LanceVectorQueryBuilder(LanceQueryBuilder):
         self._nprobes = nprobes
         return self
 
+    def ef(self, ef: int) -> LanceVectorQueryBuilder:
+        """Set the number of candidates to consider during search.
+
+        Higher values will yield better recall (more likely to find vectors if
+        they exist) at the expense of latency.
+
+        This only applies to the HNSW-related index.
+        The default value is 1.5 * limit.
+
+        Parameters
+        ----------
+        ef: int
+            The number of candidates to consider during search.
+
+        Returns
+        -------
+        LanceVectorQueryBuilder
+            The LanceQueryBuilder object.
+        """
+        self._ef = ef
+        return self
+
     def refine_factor(self, refine_factor: int) -> LanceVectorQueryBuilder:
         """Set the refine factor to use, increasing the number of vectors sampled.
 
@@ -700,6 +725,7 @@ class LanceVectorQueryBuilder(LanceQueryBuilder):
             with_row_id=self._with_row_id,
             offset=self._offset,
             fast_search=self._fast_search,
+            ef=self._ef,
         )
         result_set = self._table._execute_query(query, batch_size)
         if self._reranker is not None:
@@ -1071,6 +1097,8 @@ class LanceHybridQueryBuilder(LanceQueryBuilder):
             self._vector_query.nprobes(self._nprobes)
         if self._refine_factor:
             self._vector_query.refine_factor(self._refine_factor)
+        if self._ef:
+            self._vector_query.ef(self._ef)
 
         with ThreadPoolExecutor() as executor:
             fts_future = executor.submit(self._fts_query.with_row_id(True).to_arrow)
@@ -1197,6 +1225,29 @@ class LanceHybridQueryBuilder(LanceQueryBuilder):
         self._nprobes = nprobes
         return self
 
+    def ef(self, ef: int) -> LanceHybridQueryBuilder:
+        """
+        Set the number of candidates to consider during search.
+
+        Higher values will yield better recall (more likely to find vectors if
+        they exist) at the expense of latency.
+
+        This only applies to the HNSW-related index.
+        The default value is 1.5 * limit.
+
+        Parameters
+        ----------
+        ef: int
+            The number of candidates to consider during search.
+
+        Returns
+        -------
+        LanceHybridQueryBuilder
+            The LanceHybridQueryBuilder object.
+        """
+        self._ef = ef
+        return self
+
     def metric(self, metric: Literal["L2", "cosine", "dot"]) -> LanceHybridQueryBuilder:
         """Set the distance metric to use.
 
@@ -1644,6 +1695,21 @@ class AsyncVectorQuery(AsyncQueryBase):
         self._inner.nprobes(nprobes)
         return self
 
+    def ef(self, ef: int) -> AsyncVectorQuery:
+        """
+        Set the number of candidates to consider during search
+
+        This argument is only used when the vector column has an HNSW index.
+        If there is no index then this value is ignored.
+
+        Increasing this value will increase the recall of your query but will also
+        increase the latency of your query.  The default value is 1.5 * limit.  This
+        default is good for many cases but the best value to use will depend on your
+        data and the recall that you need to achieve.
+        """
+        self._inner.ef(ef)
+        return self
+
     def refine_factor(self, refine_factor: int) -> AsyncVectorQuery:
         """
         A multiplier to control how many additional rows are taken during the refine

python/python/lancedb/table.py

@@ -1959,6 +1959,7 @@ class LanceTable(Table):
                 "metric": query.metric,
                 "nprobes": query.nprobes,
                 "refine_factor": query.refine_factor,
+                "ef": query.ef,
             }
         return ds.scanner(
             columns=query.columns,
@@ -2736,6 +2737,8 @@ class AsyncTable:
                 async_query = async_query.refine_factor(query.refine_factor)
             if query.vector_column:
                 async_query = async_query.column(query.vector_column)
+            if query.ef:
+                async_query = async_query.ef(query.ef)
 
         if not query.prefilter:
             async_query = async_query.postfilter()

python/python/tests/test_remote_db.py

@@ -185,6 +185,7 @@ def test_query_sync_minimal():
             "k": 10,
             "prefilter": False,
             "refine_factor": None,
+            "ef": None,
             "vector": [1.0, 2.0, 3.0],
             "nprobes": 20,
         }
@@ -223,6 +224,7 @@ def test_query_sync_maximal():
             "refine_factor": 10,
             "vector": [1.0, 2.0, 3.0],
             "nprobes": 5,
+            "ef": None,
             "filter": "id > 0",
             "columns": ["id", "name"],
             "vector_column": "vector2",
@@ -318,6 +320,7 @@ def test_query_sync_hybrid():
                 "refine_factor": None,
                 "vector": [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0],
                 "nprobes": 20,
+                "ef": None,
                 "with_row_id": True,
             }
             return pa.table({"_rowid": [1, 2, 3], "_distance": [0.1, 0.2, 0.3]})

python/src/query.rs

@@ -195,6 +195,10 @@ impl VectorQuery {
         self.inner = self.inner.clone().nprobes(nprobe as usize);
     }
 
+    pub fn ef(&mut self, ef: u32) {
+        self.inner = self.inner.clone().ef(ef as usize);
+    }
+
     pub fn bypass_vector_index(&mut self) {
         self.inner = self.inner.clone().bypass_vector_index()
     }

rust/lancedb/src/query.rs

@@ -704,6 +704,9 @@ pub struct VectorQuery {
     // IVF PQ - ANN search.
     pub(crate) query_vector: Vec<Arc<dyn Array>>,
     pub(crate) nprobes: usize,
+    // The number of candidates to return during the refine step for HNSW,
+    // defaults to 1.5 * limit.
+    pub(crate) ef: Option<usize>,
     pub(crate) refine_factor: Option<u32>,
     pub(crate) distance_type: Option<DistanceType>,
     /// Default is true. Set to false to enforce a brute force search.
@@ -717,6 +720,7 @@ impl VectorQuery {
             column: None,
             query_vector: Vec::new(),
             nprobes: 20,
+            ef: None,
             refine_factor: None,
             distance_type: None,
             use_index: true,
@@ -776,6 +780,18 @@ impl VectorQuery {
         self
     }
 
+    /// Set the number of candidates to return during the refine step for HNSW
+    ///
+    /// This argument is only used when the vector column has an HNSW index.
+    /// If there is no index then this value is ignored.
+    ///
+    /// Increasing this value will increase the recall of your query but will
+    /// also increase the latency of your query.  The default value is 1.5*limit.
+    pub fn ef(mut self, ef: usize) -> Self {
+        self.ef = Some(ef);
+        self
+    }
+
     /// A multiplier to control how many additional rows are taken during the refine step
     ///
     /// This argument is only used when the vector column has an IVF PQ index.

rust/lancedb/src/remote/table.rs

@@ -196,6 +196,7 @@ impl<S: HttpSend> RemoteTable<S> {
         body["prefilter"] = query.base.prefilter.into();
         body["distance_type"] = serde_json::json!(query.distance_type.unwrap_or_default());
         body["nprobes"] = query.nprobes.into();
+        body["ef"] = query.ef.into();
         body["refine_factor"] = query.refine_factor.into();
         if let Some(vector_column) = query.column.as_ref() {
             body["vector_column"] = serde_json::Value::String(vector_column.clone());
@@ -1121,6 +1122,7 @@ mod tests {
                 "prefilter": true,
                 "distance_type": "l2",
                 "nprobes": 20,
+                "ef": Option::<usize>::None,
                 "refine_factor": null,
             });
             // Pass vector separately to make sure it matches f32 precision.
@@ -1166,6 +1168,7 @@ mod tests {
                 "bypass_vector_index": true,
                 "columns": ["a", "b"],
                 "nprobes": 12,
+                "ef": Option::<usize>::None,
                 "refine_factor": 2,
             });
             // Pass vector separately to make sure it matches f32 precision.

rust/lancedb/src/table.rs

@@ -1904,6 +1904,9 @@ impl TableInternal for NativeTable {
             query.base.offset.map(|offset| offset as i64),
         )?;
         scanner.nprobs(query.nprobes);
+        if let Some(ef) = query.ef {
+            scanner.ef(ef);
+        }
         scanner.use_index(query.use_index);
         scanner.prefilter(query.base.prefilter);
         match query.base.select {