Perf/fix: stop building a full-library IN filter for unrestricted RAG context

get_context_for_document() always materialized every document id a user
can see into a Python list, even for a superuser (or no user at all),
passing it through as a SQL IN filter. For a superuser, that's the whole
library:

- Past ~32,763 documents, this crashes outright:
  sqlite3.OperationalError: too many SQL variables (SQLite's
  SQLITE_MAX_VARIABLE_NUMBER is 32766 by default, and the query already
  binds embedding + k + a NE self-exclusion clause alongside the ids).
- Below that cliff, vec0's IN-list evaluation is a nested loop (strncmp
  per row per allowed id), so it's quadratic in library size for no
  reason -- the filter was never going to exclude anything.

get_objects_for_user_owner_aware() already returns every Document for a
superuser (guardian's own with_superuser shortcut), so skipping straight
to document_ids=None changes nothing about which documents are
considered, only how we get there.

Also:
- Drop the pointless sorted() in _document_id_filters(): a SQL IN clause
  doesn't care about order, so it was pure overhead on every call.
- Add a hard guard in _build_where() so a future regression (or a
  legitimately huge permission-restricted user) fails closed -- no rows,
  a logged warning -- instead of a cryptic OperationalError. Since this
  filter scopes document access, failing closed rather than skipping the
  filter is the only safe way to handle an oversized list.

First item from VECTOR_STORE_PERF_BACKLOG.md (an audit done alongside
perf/13314-vecstore-point-delete, deferred to its own branch since that
one was already large).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/paperless_ai/ai_classifier.py

@@ -96,19 +96,26 @@ def get_context_for_document(
     user: User | None = None,
     max_docs: int = 5,
 ) -> str:
-    visible_documents = (
-        get_objects_for_user_owner_aware(
-            user,
-            "view_document",
-            Document,
-        )
-        if user
-        else None
-    )
+    # None means "no restriction" to query_similar_documents. A superuser
+    # (like no user at all) can see every document, so skip materializing
+    # every visible pk into a Python list and passing it through as a SQL
+    # IN filter: for a large library that is a wasted quadratic scan in the
+    # vector store at best, and past ~32,763 documents a hard
+    # sqlite3.OperationalError (SQLite's bound-parameter limit) at worst.
+    # get_objects_for_user_owner_aware() would return every Document for a
+    # superuser anyway (guardian's own with_superuser shortcut), so this
+    # changes nothing about which documents are considered -- only how we
+    # get there.
     visible_document_ids = (
-        list(visible_documents.values_list("pk", flat=True))
-        if visible_documents is not None
-        else None
+        None
+        if user is None or user.is_superuser
+        else list(
+            get_objects_for_user_owner_aware(
+                user,
+                "view_document",
+                Document,
+            ).values_list("pk", flat=True),
+        )
     )
     similar_docs = query_similar_documents(
         document=doc,

src/paperless_ai/indexing.py

@@ -397,7 +397,7 @@ def _document_id_filters(doc_ids):
             MetadataFilter(
                 key="document_id",
                 operator=FilterOperator.IN,
-                value=sorted(doc_ids),
+                value=list(doc_ids),
             ),
         ],
     )

src/paperless_ai/tests/test_ai_classifier.py

@@ -3,6 +3,8 @@ from unittest.mock import MagicMock
 from unittest.mock import patch
 
 import pytest
+import pytest_mock
+from django.contrib.auth.models import User
 from django.test import override_settings
 
 from documents.models import Document
@@ -278,3 +280,104 @@ def test_get_context_for_document_no_similar_docs(mock_document):
     with patch("paperless_ai.ai_classifier.query_similar_documents", return_value=[]):
         result = get_context_for_document(mock_document)
         assert result == ""
+
+
+class TestGetContextForDocumentVisibility:
+    """get_context_for_document must not materialize every visible document
+    id for a user who can already see the whole library: a superuser (like
+    no user at all) gets document_ids=None (no restriction) straight
+    through to query_similar_documents(), instead of a full-library IN
+    filter that is wasteful at best and, past ~32,763 documents, a hard
+    sqlite3.OperationalError at worst (SQLite's bound-parameter limit).
+    """
+
+    def test_skips_permission_lookup_for_superuser(
+        self,
+        mock_document: MagicMock,
+        mock_similar_documents: list[MagicMock],
+        mocker: pytest_mock.MockerFixture,
+    ) -> None:
+        """
+        GIVEN:
+            - A superuser
+        WHEN:
+            - get_context_for_document() is called
+        THEN:
+            - get_objects_for_user_owner_aware() is never called, and
+              query_similar_documents() is called with document_ids=None
+        """
+        mock_query = mocker.patch(
+            "paperless_ai.ai_classifier.query_similar_documents",
+            return_value=mock_similar_documents,
+        )
+        mock_get_objects = mocker.patch(
+            "paperless_ai.ai_classifier.get_objects_for_user_owner_aware",
+        )
+        user = mocker.MagicMock(spec=User)
+        user.is_superuser = True
+
+        get_context_for_document(mock_document, user, max_docs=2)
+
+        mock_get_objects.assert_not_called()
+        assert mock_query.call_args.kwargs["document_ids"] is None
+
+    def test_skips_permission_lookup_when_no_user(
+        self,
+        mock_document: MagicMock,
+        mock_similar_documents: list[MagicMock],
+        mocker: pytest_mock.MockerFixture,
+    ) -> None:
+        """
+        GIVEN:
+            - No user (user=None)
+        WHEN:
+            - get_context_for_document() is called
+        THEN:
+            - get_objects_for_user_owner_aware() is never called, and
+              query_similar_documents() is called with document_ids=None
+        """
+        mock_query = mocker.patch(
+            "paperless_ai.ai_classifier.query_similar_documents",
+            return_value=mock_similar_documents,
+        )
+        mock_get_objects = mocker.patch(
+            "paperless_ai.ai_classifier.get_objects_for_user_owner_aware",
+        )
+
+        get_context_for_document(mock_document, None, max_docs=2)
+
+        mock_get_objects.assert_not_called()
+        assert mock_query.call_args.kwargs["document_ids"] is None
+
+    def test_restricts_to_visible_documents_for_non_superuser(
+        self,
+        mock_document: MagicMock,
+        mock_similar_documents: list[MagicMock],
+        mocker: pytest_mock.MockerFixture,
+    ) -> None:
+        """
+        GIVEN:
+            - A non-superuser with a specific set of visible documents
+        WHEN:
+            - get_context_for_document() is called
+        THEN:
+            - query_similar_documents() is called with exactly that user's
+              visible document ids, unchanged from before this optimization
+        """
+        mock_query = mocker.patch(
+            "paperless_ai.ai_classifier.query_similar_documents",
+            return_value=mock_similar_documents,
+        )
+        mock_queryset = mocker.MagicMock()
+        mock_queryset.values_list.return_value = [1, 2, 3]
+        mock_get_objects = mocker.patch(
+            "paperless_ai.ai_classifier.get_objects_for_user_owner_aware",
+            return_value=mock_queryset,
+        )
+        user = mocker.MagicMock(spec=User)
+        user.is_superuser = False
+
+        get_context_for_document(mock_document, user, max_docs=2)
+
+        mock_get_objects.assert_called_once_with(user, "view_document", Document)
+        assert mock_query.call_args.kwargs["document_ids"] == [1, 2, 3]

src/paperless_ai/tests/test_vector_store.py

@@ -17,6 +17,7 @@ from paperless_ai.migrations import Migration
 from paperless_ai.migrations import m0001_v1_to_v2
 from paperless_ai.tables import DocumentChunksTable
 from paperless_ai.tables import DocumentMetaTable
+from paperless_ai.vector_store import _MAX_IN_VALUES
 from paperless_ai.vector_store import DB_FILENAME
 from paperless_ai.vector_store import DEFAULT_TABLE_NAME
 from paperless_ai.vector_store import SCHEMA_VERSION
@@ -296,8 +297,47 @@ class TestBuildWhere:
         assert where == "1 = 0"
         assert params == []
 
-    def test_query_with_untranslatable_filter_returns_no_rows(self, store) -> None:
-        store.add([make_node("a1", 1), make_node("b1", 2)])
+    def test_fails_closed_when_in_filter_exceeds_max_values(
+        self,
+        caplog: pytest.LogCaptureFixture,
+    ) -> None:
+        """
+        GIVEN:
+            - An IN filter with more values than _MAX_IN_VALUES (SQLite's
+              own bound-parameter limit is 32766; this guard sits below
+              that with headroom for the query's other bound parameters)
+        WHEN:
+            - _build_where() translates it to SQL
+        THEN:
+            - It fails closed ("1 = 0", no params) instead of building an
+              IN clause SQLite would reject, and logs a warning -- this
+              filter scopes document access, so refusing to build it must
+              never widen the scope to "everything" by accident
+        """
+        oversized = _in_filter([str(i) for i in range(_MAX_IN_VALUES + 1)])
+
+        with caplog.at_level("WARNING"):
+            where, params = _build_where(oversized)
+
+        assert where == "(1 = 0)"
+        assert params == []
+        assert "document_id" in caplog.text
+
+    def test_query_with_untranslatable_filter_returns_no_rows(
+        self,
+        store: PaperlessSqliteVecVectorStore,
+    ) -> None:
+        """
+        GIVEN:
+            - A store with one chunk each for documents 1 and 2
+        WHEN:
+            - A query and a get_nodes() call are issued with a filter whose
+              only clause is an untranslatable nested MetadataFilters
+        THEN:
+            - Neither call raises, and both fail closed by returning no rows
+              (rather than emitting invalid or unfiltered SQL)
+        """
+        store.add([make_node("a1", "1"), make_node("b1", "2")])
         nested = MetadataFilters(
             filters=[
                 MetadataFilter(

src/paperless_ai/vector_store.py

@@ -75,6 +75,17 @@ class _Row(NamedTuple):
     embedding: bytes
 
 
+# _build_where(): the largest IN value list translated into bound SQL
+# parameters. SQLite's own hard limit (SQLITE_MAX_VARIABLE_NUMBER) is 32766
+# by default; this leaves headroom below that for the query's other bound
+# parameters (the embedding blob, k, and any NE clause) and for the limit
+# itself to move. An IN filter this large should not happen in practice --
+# callers are expected to pass None (no filter) rather than every id when
+# the filter would not actually narrow anything -- so this is a guard
+# against a future regression, not a normal code path.
+_MAX_IN_VALUES = 32700
+
+
 def _pack(embedding: Sequence[float]) -> bytes:
     return struct.pack(f"{len(embedding)}f", *embedding)
 
@@ -119,6 +130,21 @@ def _build_where(filters: MetadataFilters | None) -> tuple[str, list[int]]:
             if not values:  # pragma: no cover
                 clauses.append("1 = 0")
                 continue
+            if len(values) > _MAX_IN_VALUES:
+                # Fail closed (see the empty-clauses case below) rather than
+                # let SQLite raise "too many SQL variables" past its own
+                # limit: this filter scopes document access, so an IN list
+                # too large to safely bind must match no rows, never widen
+                # the scope to "everything" by accident.
+                logger.warning(
+                    "Refusing to build an IN filter on %r with %d values "
+                    "(over the %d-value safety limit); returning no rows.",
+                    f.key,
+                    len(values),
+                    _MAX_IN_VALUES,
+                )
+                clauses.append("1 = 0")
+                continue
             placeholders = ",".join("?" for _ in values)
             clauses.append(f"{f.key} IN ({placeholders})")
             params.extend(values)