feat: add drop_index

protos/transaction.proto

@@ -67,7 +67,9 @@ message Transaction {
 
   // Add or replace a new secondary index.
   //
-  // - new_indices: the modified indices
+  // This is also used to remove an index (we are replacing it with nothing)
+  //
+  // - new_indices: the modified indices, empty if dropping indices only
   // - removed_indices: the indices that are being replaced
   message CreateIndex {
     repeated IndexMetadata new_indices = 1;

python/python/lance/dataset.py

@@ -2222,6 +2222,17 @@ def create_index(
             )
         return self
 
+    def drop_index(self, name: str):
+        """
+        Drops an index from the dataset
+
+        Note: Indices are dropped by "index name".  This is not the same as the field
+        name. If you did not specify a name when you created the index then a name was
+        generated for you.  You can use the `list_indices` method to get the names of
+        the indices.
+        """
+        return self._ds.drop_index(name)
+
     def session(self) -> Session:
         """
         Return the dataset session, which holds the dataset's state.

python/python/lance/lance/__init__.pyi

@@ -265,6 +265,7 @@ class _Dataset:
         storage_options: Optional[Dict[str, str]] = None,
         kwargs: Optional[Dict[str, Any]] = None,
     ): ...
+    def drop_index(self, name: str): ...
     def count_fragments(self) -> int: ...
     def num_small_files(self, max_rows_per_group: int) -> int: ...
     def get_fragments(self) -> List[_Fragment]: ...

python/python/tests/test_scalar_index.py

@@ -675,3 +675,35 @@ def test_optimize_no_new_data(tmp_path: Path):
 
     assert dataset.to_table(filter="btree IS NULL").num_rows == 2
     assert dataset.to_table(filter="bitmap IS NULL").num_rows == 2
+
+
+def test_drop_index(tmp_path):
+    test_table_size = 100
+    test_table = pa.table(
+        {
+            "btree": list(range(test_table_size)),
+            "bitmap": list(range(test_table_size)),
+            "fts": ["a" for _ in range(test_table_size)],
+        }
+    )
+    ds = lance.write_dataset(test_table, tmp_path)
+    ds.create_scalar_index("btree", index_type="BTREE")
+    ds.create_scalar_index("bitmap", index_type="BITMAP")
+    ds.create_scalar_index("fts", index_type="INVERTED")
+
+    assert len(ds.list_indices()) == 3
+
+    # Attempt to drop index (name does not exist)
+    with pytest.raises(RuntimeError, match="index not found"):
+        ds.drop_index("nonexistent_name")
+
+    for idx in ds.list_indices():
+        idx_name = idx["name"]
+        ds.drop_index(idx_name)
+
+    assert len(ds.list_indices()) == 0
+
+    # Ensure we can still search columns
+    assert ds.to_table(filter="btree = 1").num_rows == 1
+    assert ds.to_table(filter="bitmap = 1").num_rows == 1
+    assert ds.to_table(filter="fts = 'a'").num_rows == test_table_size

python/python/tests/test_vector_index.py

@@ -1105,3 +1105,27 @@ def test_optimize_indices(indexed_dataset):
     indexed_dataset.optimize.optimize_indices(num_indices_to_merge=0)
     indices = indexed_dataset.list_indices()
     assert len(indices) == 2
+
+
+def test_drop_indices(indexed_dataset):
+    idx_name = indexed_dataset.list_indices()[0]["name"]
+
+    indexed_dataset.drop_index(idx_name)
+    indices = indexed_dataset.list_indices()
+    assert len(indices) == 0
+
+    test_vec = (
+        indexed_dataset.take([0], columns=["vector"]).column("vector").to_pylist()[0]
+    )
+
+    # make sure we can still search the column (will do flat search)
+    results = indexed_dataset.to_table(
+        nearest={
+            "column": "vector",
+            "q": test_vec,
+            "k": 15,
+            "nprobes": 1,
+        },
+    )
+
+    assert len(results) == 15

python/src/dataset.rs

@@ -1266,6 +1266,15 @@ impl Dataset {
         Ok(())
     }
 
+    fn drop_index(&mut self, name: &str) -> PyResult<()> {
+        let mut new_self = self.ds.as_ref().clone();
+        RT.block_on(None, new_self.drop_index(name))?
+            .infer_error()?;
+        self.ds = Arc::new(new_self);
+
+        Ok(())
+    }
+
     fn count_fragments(&self) -> usize {
         self.ds.count_fragments()
     }

rust/lance-index/src/traits.rs

@@ -34,6 +34,15 @@ pub trait DatasetIndexExt {
         replace: bool,
     ) -> Result<()>;
 
+    /// Drop indices by name.
+    ///
+    /// Upon finish, a new dataset version is generated.
+    ///
+    /// Parameters:
+    ///
+    /// - `name`: the name of the index to drop.
+    async fn drop_index(&mut self, name: &str) -> Result<()>;
+
     /// Read all indices of this Dataset version.
     ///
     /// The indices are lazy loaded and cached in memory within the [`Dataset`] instance.

rust/lance/src/index.rs

@@ -347,6 +347,42 @@ impl DatasetIndexExt for Dataset {
         Ok(())
     }
 
+    async fn drop_index(&mut self, name: &str) -> Result<()> {
+        let indices = self.load_indices_by_name(name).await?;
+        if indices.is_empty() {
+            return Err(Error::IndexNotFound {
+                identity: format!("name={}", name),
+                location: location!(),
+            });
+        }
+
+        let transaction = Transaction::new(
+            self.manifest.version,
+            Operation::CreateIndex {
+                new_indices: vec![],
+                removed_indices: indices.clone(),
+            },
+            /*blobs_op= */ None,
+            None,
+        );
+
+        let (new_manifest, manifest_path) = commit_transaction(
+            self,
+            self.object_store(),
+            self.commit_handler.as_ref(),
+            &transaction,
+            &Default::default(),
+            &Default::default(),
+            self.manifest_naming_scheme,
+        )
+        .await?;
+
+        self.manifest = Arc::new(new_manifest);
+        self.manifest_file = manifest_path;
+
+        Ok(())
+    }
+
     async fn load_indices(&self) -> Result<Arc<Vec<IndexMetadata>>> {
         let dataset_dir = self.base.to_string();
         if let Some(indices) = self
@@ -909,6 +945,7 @@ impl DatasetIndexInternalExt for Dataset {
 #[cfg(test)]
 mod tests {
     use crate::dataset::builder::DatasetBuilder;
+    use crate::utils::test::{DatagenExt, FragmentCount, FragmentRowCount};
 
     use super::*;
 
@@ -984,19 +1021,79 @@ mod tests {
             .is_err());
     }
 
-    #[tokio::test]
-    async fn test_count_index_rows() {
-        let test_dir = tempdir().unwrap();
+    fn sample_vector_field() -> Field {
         let dimensions = 16;
         let column_name = "vec";
-        let field = Field::new(
+        Field::new(
             column_name,
             DataType::FixedSizeList(
                 Arc::new(Field::new("item", DataType::Float32, true)),
                 dimensions,
             ),
             false,
-        );
+        )
+    }
+
+    #[tokio::test]
+    async fn test_drop_index() {
+        let test_dir = tempdir().unwrap();
+        let schema = Schema::new(vec![
+            sample_vector_field(),
+            Field::new("ints", DataType::Int32, false),
+        ]);
+        let mut dataset = lance_datagen::rand(&schema)
+            .into_dataset(
+                test_dir.path().to_str().unwrap(),
+                FragmentCount::from(1),
+                FragmentRowCount::from(256),
+            )
+            .await
+            .unwrap();
+
+        let idx_name = "name".to_string();
+        dataset
+            .create_index(
+                &["vec"],
+                IndexType::Vector,
+                Some(idx_name.clone()),
+                &VectorIndexParams::ivf_pq(2, 8, 2, MetricType::L2, 10),
+                true,
+            )
+            .await
+            .unwrap();
+        dataset
+            .create_index(
+                &["ints"],
+                IndexType::BTree,
+                None,
+                &ScalarIndexParams::default(),
+                true,
+            )
+            .await
+            .unwrap();
+
+        assert_eq!(dataset.load_indices().await.unwrap().len(), 2);
+
+        dataset.drop_index(&idx_name).await.unwrap();
+
+        assert_eq!(dataset.load_indices().await.unwrap().len(), 1);
+
+        // Even though we didn't give the scalar index a name it still has an auto-generated one we can use
+        let scalar_idx_name = &dataset.load_indices().await.unwrap()[0].name;
+        dataset.drop_index(scalar_idx_name).await.unwrap();
+
+        assert_eq!(dataset.load_indices().await.unwrap().len(), 0);
+
+        // Make sure it returns an error if the index doesn't exist
+        assert!(dataset.drop_index(scalar_idx_name).await.is_err());
+    }
+
+    #[tokio::test]
+    async fn test_count_index_rows() {
+        let test_dir = tempdir().unwrap();
+        let dimensions = 16;
+        let column_name = "vec";
+        let field = sample_vector_field();
         let schema = Arc::new(Schema::new(vec![field]));
 
         let float_arr = generate_random_array(512 * dimensions as usize);