diff --git a/docarray/index/backends/hnswlib.py b/docarray/index/backends/hnswlib.py
index 022ab8d818..9d59af0120 100644
--- a/docarray/index/backends/hnswlib.py
+++ b/docarray/index/backends/hnswlib.py
@@ -137,7 +137,7 @@ def __init__(self, db_config=None, **kwargs):
         self._column_names: List[str] = []
         self._create_docs_table()
         self._sqlite_conn.commit()
-        self._num_docs = self._get_num_docs_sqlite()
+        self._num_docs = 0  # recompute again when needed
         self._logger.info(f'{self.__class__.__name__} has been initialized')
 
     @property
@@ -281,7 +281,7 @@ def index(self, docs: Union[BaseDoc, Sequence[BaseDoc]], **kwargs):
 
         self._send_docs_to_sqlite(docs_validated)
         self._sqlite_conn.commit()
-        self._num_docs = self._get_num_docs_sqlite()
+        self._num_docs = 0  # recompute again when needed
 
     def execute_query(self, query: List[Tuple[str, Dict]], *args, **kwargs) -> Any:
         """
@@ -318,9 +318,6 @@ def _find_batched(
     def _find(
         self, query: np.ndarray, limit: int, search_field: str = ''
     ) -> _FindResult:
-        if self.num_docs() == 0:
-            return _FindResult(documents=[], scores=[])  # type: ignore
-
         query_batched = np.expand_dims(query, axis=0)
         docs, scores = self._find_batched(
             queries=query_batched, limit=limit, search_field=search_field
@@ -385,7 +382,7 @@ def _del_items(self, doc_ids: Sequence[str]):
 
         self._delete_docs_from_sqlite(doc_ids)
         self._sqlite_conn.commit()
-        self._num_docs = self._get_num_docs_sqlite()
+        self._num_docs = 0  # recompute again when needed
 
     def _get_items(self, doc_ids: Sequence[str], out: bool = True) -> Sequence[TSchema]:
         """Get Documents from the hnswlib index, by `id`.
@@ -410,6 +407,8 @@ def num_docs(self) -> int:
         """
         Get the number of documents.
         """
+        if self._num_docs == 0:
+            self._num_docs = self._get_num_docs_sqlite()
         return self._num_docs
 
     ###############################################
@@ -605,7 +604,7 @@ def _search_and_filter(
             documents and their corresponding scores.
         """
         # If there are no documents or hashed_ids is an empty set, return an empty _FindResultBatched
-        if self.num_docs() == 0 or (hashed_ids is not None and len(hashed_ids) == 0):
+        if hashed_ids is not None and len(hashed_ids) == 0:
             return _FindResultBatched(documents=[], scores=[])  # type: ignore
 
         # Set limit as the minimum of the provided limit and the total number of documents
@@ -628,8 +627,11 @@ def accept_hashed_ids(id):
 
         # If hashed_ids is provided, k is the minimum of limit and the length of hashed_ids; else it is limit
         k = min(limit, len(hashed_ids)) if hashed_ids else limit
-
-        labels, distances = index.knn_query(queries, k=k, **extra_kwargs)
+        try:
+            labels, distances = index.knn_query(queries, k=k, **extra_kwargs)
+        except RuntimeError:  # logic to avoid calling num_docs in most of the cases which comes at performance cost when many docs are indexed
+            k = min(k, self.num_docs())
+            labels, distances = index.knn_query(queries, k=k, **extra_kwargs)
 
         result_das = [
             self._get_docs_sqlite_hashed_id(