feat: support to build FTS without positions (#1621)

docs/src/fts.md

@@ -62,7 +62,7 @@ Consider that we have a LanceDB table named `my_table`, whose string column `tex
     });
 
     await tbl
-        .search("puppy")
+        .search("puppy", queryType="fts")
         .select(["text"])
         .limit(10)
         .toArray();
@@ -205,7 +205,7 @@ table.create_fts_index(["text_field"], use_tantivy=True, ordering_field_names=["
 ## Phrase queries vs. terms queries
 
 !!! warning "Warn"
-    Phrase queries are available for only Tantivy-based FTS
+    Lance-based FTS doesn't support queries combining by boolean operators `OR`, `AND`.
 
 For full-text search you can specify either a **phrase** query like `"the old man and the sea"`,
 or a **terms** search query like `"(Old AND Man) AND Sea"`. For more details on the terms

nodejs/__test__/table.test.ts

@@ -844,6 +844,38 @@ describe.each([arrow13, arrow14, arrow15, arrow16, arrow17])(
       expect(results[0].text).toBe(data[0].text);
     });
 
+    test("full text search without positions", async () => {
+      const db = await connect(tmpDir.name);
+      const data = [
+        { text: "hello world", vector: [0.1, 0.2, 0.3] },
+        { text: "goodbye world", vector: [0.4, 0.5, 0.6] },
+      ];
+      const table = await db.createTable("test", data);
+      await table.createIndex("text", {
+        config: Index.fts({ withPositions: false }),
+      });
+
+      const results = await table.search("hello").toArray();
+      expect(results[0].text).toBe(data[0].text);
+    });
+
+    test("full text search phrase query", async () => {
+      const db = await connect(tmpDir.name);
+      const data = [
+        { text: "hello world", vector: [0.1, 0.2, 0.3] },
+        { text: "goodbye world", vector: [0.4, 0.5, 0.6] },
+      ];
+      const table = await db.createTable("test", data);
+      await table.createIndex("text", {
+        config: Index.fts(),
+      });
+
+      const results = await table.search("world").toArray();
+      expect(results.length).toBe(2);
+      const phraseResults = await table.search('"hello world"').toArray();
+      expect(phraseResults.length).toBe(1);
+    });
+
     test.each([
       [0.4, 0.5, 0.599], // number[]
       Float32Array.of(0.4, 0.5, 0.599), // Float32Array

nodejs/lancedb/indices.ts

@@ -113,6 +113,19 @@ export interface IvfPqOptions {
   sampleRate?: number;
 }
 
+/**
+ * Options to create a full text search index
+ */
+export interface FtsOptions {
+  /**
+   * Whether to build the index with positions.
+   * True by default.
+   * If set to false, the index will not store the positions of the tokens in the text,
+   * which will make the index smaller and faster to build, but will not support phrase queries.
+   */
+  withPositions?: boolean;
+}
+
 export class Index {
   private readonly inner: LanceDbIndex;
   private constructor(inner: LanceDbIndex) {
@@ -211,8 +224,8 @@ export class Index {
    *
    * For now, the full text search index only supports English, and doesn't support phrase search.
    */
-  static fts() {
-    return new Index(LanceDbIndex.fts());
+  static fts(options?: Partial<FtsOptions>) {
+    return new Index(LanceDbIndex.fts(options?.withPositions));
   }
 }
 

nodejs/src/index.rs

@@ -92,9 +92,13 @@ impl Index {
     }
 
     #[napi(factory)]
-    pub fn fts() -> Self {
+    pub fn fts(with_position: Option<bool>) -> Self {
+        let mut opts = FtsIndexBuilder::default();
+        if let Some(with_position) = with_position {
+            opts = opts.with_position(with_position);
+        }
         Self {
-            inner: Mutex::new(Some(LanceDbIndex::FTS(FtsIndexBuilder::default()))),
+            inner: Mutex::new(Some(LanceDbIndex::FTS(opts))),
         }
     }
 }

python/python/lancedb/index.py

@@ -78,8 +78,8 @@ class FTS:
     For example, it works with `title`, `description`, `content`, etc.
     """
 
-    def __init__(self):
-        self._inner = LanceDbIndex.fts()
+    def __init__(self, with_position: bool = True):
+        self._inner = LanceDbIndex.fts(with_position=with_position)
 
 
 class IvfPq:

python/python/lancedb/remote/table.py

@@ -126,6 +126,7 @@ class RemoteTable(Table):
         column: str,
         *,
         replace: bool = False,
+        with_position: bool = True,
     ):
         data = {
             "column": column,

python/python/lancedb/table.py

@@ -468,6 +468,7 @@ class Table(ABC):
         ordering_field_names: Union[str, List[str]] = None,
         *,
         replace: bool = False,
+        with_position: bool = True,
         writer_heap_size: Optional[int] = 1024 * 1024 * 1024,
         tokenizer_name: str = "default",
         use_tantivy: bool = True,
@@ -500,6 +501,12 @@ class Table(ABC):
         use_tantivy: bool, default True
             If True, use the legacy full-text search implementation based on tantivy.
             If False, use the new full-text search implementation based on lance-index.
+        with_position: bool, default True
+            Only available with use_tantivy=False
+            If False, do not store the positions of the terms in the text.
+            This can reduce the size of the index and improve indexing speed.
+            But it will not be possible to use phrase queries.
+
         """
         raise NotImplementedError
 
@@ -1305,6 +1312,7 @@ class LanceTable(Table):
         ordering_field_names: Union[str, List[str]] = None,
         *,
         replace: bool = False,
+        with_position: bool = True,
         writer_heap_size: Optional[int] = 1024 * 1024 * 1024,
         tokenizer_name: str = "default",
         use_tantivy: bool = True,
@@ -1318,7 +1326,10 @@ class LanceTable(Table):
                 if exist:
                     fs.delete_dir(path)
             self._dataset_mut.create_scalar_index(
-                field_names, index_type="INVERTED", replace=replace
+                field_names,
+                index_type="INVERTED",
+                replace=replace,
+                with_position=with_position,
             )
             return
 

python/python/tests/test_fts.py

@@ -140,8 +140,11 @@ def test_create_index_with_stemming(tmp_path, table):
 
 
 @pytest.mark.parametrize("use_tantivy", [True, False])
-def test_create_inverted_index(table, use_tantivy):
-    table.create_fts_index("text", use_tantivy=use_tantivy)
+@pytest.mark.parametrize("with_position", [True, False])
+def test_create_inverted_index(table, use_tantivy, with_position):
+    if use_tantivy and not with_position:
+        pytest.skip("we don't support to build tantivy index without position")
+    table.create_fts_index("text", use_tantivy=use_tantivy, with_position=with_position)
 
 
 def test_populate_index(tmp_path, table):
@@ -166,6 +169,40 @@ def test_search_fts(table, use_tantivy):
     assert len(results) == 5
 
 
+def test_search_fts_phrase_query(table):
+    table.create_fts_index("text", use_tantivy=False, with_position=False)
+    try:
+        phrase_results = table.search('"puppy runs"').limit(100).to_list()
+        assert False
+    except Exception:
+        pass
+    table.create_fts_index("text", use_tantivy=False, replace=True)
+    results = table.search("puppy").limit(100).to_list()
+    phrase_results = table.search('"puppy runs"').limit(100).to_list()
+    assert len(results) > len(phrase_results)
+    assert len(phrase_results) > 0
+
+
+@pytest.mark.asyncio
+async def test_search_fts_phrase_query_async(async_table):
+    async_table = await async_table
+    await async_table.create_index("text", config=FTS(with_position=False))
+    try:
+        phrase_results = (
+            await async_table.query().nearest_to_text("puppy runs").limit(100).to_list()
+        )
+        assert False
+    except Exception:
+        pass
+    await async_table.create_index("text", config=FTS())
+    results = await async_table.query().nearest_to_text("puppy").limit(100).to_list()
+    phrase_results = (
+        await async_table.query().nearest_to_text('"puppy runs"').limit(100).to_list()
+    )
+    assert len(results) > len(phrase_results)
+    assert len(phrase_results) > 0
+
+
 def test_search_fts_specify_column(table):
     table.create_fts_index("text", use_tantivy=False)
     table.create_fts_index("text2", use_tantivy=False)

python/src/index.rs

@@ -14,6 +14,7 @@
 
 use std::sync::Mutex;
 
+use lancedb::index::scalar::FtsIndexBuilder;
 use lancedb::{
     index::{scalar::BTreeIndexBuilder, vector::IvfPqIndexBuilder, Index as LanceDbIndex},
     DistanceType,
@@ -100,10 +101,14 @@ impl Index {
     }
 
     #[staticmethod]
-    pub fn fts() -> PyResult<Self> {
-        Ok(Self {
-            inner: Mutex::new(Some(LanceDbIndex::FTS(Default::default()))),
-        })
+    pub fn fts(with_position: Option<bool>) -> Self {
+        let mut opts = FtsIndexBuilder::default();
+        if let Some(with_position) = with_position {
+            opts = opts.with_position(with_position);
+        }
+        Self {
+            inner: Mutex::new(Some(LanceDbIndex::FTS(opts))),
+        }
     }
 }
 

rust/lancedb/src/index/scalar.rs

@@ -51,9 +51,25 @@ pub struct LabelListIndexBuilder {}
 /// Builder for a full text search index
 ///
 /// A full text search index is an index on a string column that allows for full text search
-#[derive(Debug, Clone, Default)]
-pub struct FtsIndexBuilder {}
+#[derive(Debug, Clone)]
+pub struct FtsIndexBuilder {
+    pub(crate) with_position: bool,
+}
 
-impl FtsIndexBuilder {}
+impl Default for FtsIndexBuilder {
+    fn default() -> Self {
+        Self {
+            with_position: true,
+        }
+    }
+}
+
+impl FtsIndexBuilder {
+    /// Set the with_position flag
+    pub fn with_position(mut self, with_position: bool) -> Self {
+        self.with_position = with_position;
+        self
+    }
+}
 
 pub use lance_index::scalar::FullTextSearchQuery;

rust/lancedb/src/table.rs

@@ -52,6 +52,7 @@ use crate::arrow::IntoArrow;
 use crate::connection::NoData;
 use crate::embeddings::{EmbeddingDefinition, EmbeddingRegistry, MaybeEmbedded, MemoryRegistry};
 use crate::error::{Error, Result};
+use crate::index::scalar::FtsIndexBuilder;
 use crate::index::vector::{
     IvfHnswPqIndexBuilder, IvfHnswSqIndexBuilder, IvfPqIndexBuilder, VectorIndex,
 };
@@ -1609,7 +1610,12 @@ impl NativeTable {
         Ok(())
     }
 
-    async fn create_fts_index(&self, field: &Field, opts: IndexBuilder) -> Result<()> {
+    async fn create_fts_index(
+        &self,
+        field: &Field,
+        fts_opts: FtsIndexBuilder,
+        replace: bool,
+    ) -> Result<()> {
         if !Self::supported_fts_data_type(field.data_type()) {
             return Err(Error::Schema {
                 message: format!(
@@ -1621,16 +1627,16 @@ impl NativeTable {
         }
 
         let mut dataset = self.dataset.get_mut().await?;
-        let lance_idx_params = lance_index::scalar::ScalarIndexParams {
-            force_index_type: Some(lance_index::scalar::ScalarIndexType::Inverted),
+        let fts_params = lance_index::scalar::InvertedIndexParams {
+            with_position: fts_opts.with_position,
         };
         dataset
             .create_index(
                 &[field.name()],
-                IndexType::Scalar,
+                IndexType::Inverted,
                 None,
-                &lance_idx_params,
-                opts.replace,
+                &fts_params,
+                replace,
             )
             .await?;
         Ok(())
@@ -1802,7 +1808,7 @@ impl TableInternal for NativeTable {
             Index::BTree(_) => self.create_btree_index(field, opts).await,
             Index::Bitmap(_) => self.create_bitmap_index(field, opts).await,
             Index::LabelList(_) => self.create_label_list_index(field, opts).await,
-            Index::FTS(_) => self.create_fts_index(field, opts).await,
+            Index::FTS(fts_opts) => self.create_fts_index(field, fts_opts, opts.replace).await,
             Index::IvfPq(ivf_pq) => self.create_ivf_pq_index(ivf_pq, field, opts.replace).await,
             Index::IvfHnswPq(ivf_hnsw_pq) => {
                 self.create_ivf_hnsw_pq_index(ivf_hnsw_pq, field, opts.replace)