Fix: skip incremental index writes when a re-embed migration is pending

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

docker/rootfs/etc/s6-overlay/s6-rc.d/init-llmindex-migrate/run

@@ -0,0 +1,12 @@
+#!/command/with-contenv /usr/bin/bash
+# shellcheck shell=bash
+
+declare -r log_prefix="[init-llmindex-migrate]"
+
+echo "${log_prefix} Checking for pending LLM index migrations..."
+cd "${PAPERLESS_SRC_DIR}"
+if [[ -n "${USER_IS_NON_ROOT}" ]]; then
+	python3 manage.py document_llmindex migrate
+else
+	s6-setuidgid paperless python3 manage.py document_llmindex migrate
+fi

docker/rootfs/etc/s6-overlay/s6-rc.d/init-llmindex-migrate/type

@@ -0,0 +1 @@
+oneshot

docker/rootfs/etc/s6-overlay/s6-rc.d/init-llmindex-migrate/up

@@ -0,0 +1 @@
+/etc/s6-overlay/s6-rc.d/init-llmindex-migrate/run

docs/administration.md

@@ -212,6 +212,16 @@ following:
     This is a no-op if the index is already up to date, so it is safe to
     run on every upgrade.
 
+5.  Migrate the LLM index if needed.
+
+    ```shell-session
+    cd src
+    python3 manage.py document_llmindex migrate
+    ```
+
+    This is a no-op if the index schema is already current, so it is safe
+    to run on every upgrade.
+
 ### Database Upgrades
 
 Paperless-ngx is compatible with Django-supported versions of PostgreSQL and MariaDB and it is generally
@@ -532,7 +542,7 @@ index is updated automatically on the schedule set by
 can manage it manually:
 
 ```
-document_llmindex {rebuild,update,compact}
+document_llmindex {rebuild,update,compact,migrate}
 ```
 
 Specify `rebuild` to build the index from scratch from all documents in the database. Use

src-ui/src/app/components/common/pdf-viewer/pdf-viewer.component.spec.ts

@@ -129,13 +129,25 @@ describe('PngxPdfViewerComponent', () => {
     ;(component as any).applyScale()
     expect(viewer.currentScaleValue).toBe(PdfZoomScale.PageFit)
     expect(viewer.currentScale).toBe(2)
+  })
 
+  it('does not reapply scale for page-only changes', async () => {
+    await initComponent()
+
+    const pdf = (component as any).pdf as { numPages: number }
+    pdf.numPages = 3
+    const viewer = (component as any).pdfViewer as PDFViewer
+    viewer.setDocument(pdf)
     const applyScaleSpy = jest.spyOn(component as any, 'applyScale')
     component.page = 2
-    ;(component as any).lastViewerPage = 2
-    ;(component as any).applyViewerState()
+
+    component.ngOnChanges({
+      page: new SimpleChange(1, 2, false),
+    })
+
+    expect(viewer.currentPageNumber).toBe(2)
     expect((component as any).lastViewerPage).toBeUndefined()
-    expect(applyScaleSpy).toHaveBeenCalled()
+    expect(applyScaleSpy).not.toHaveBeenCalled()
   })
 
   it('does not reset the viewer when it is already on the requested page', async () => {

src-ui/src/app/components/common/pdf-viewer/pdf-viewer.component.ts

@@ -116,7 +116,10 @@ export class PngxPdfViewerComponent
       changes['zoomScale'] ||
       changes['rotation']
     ) {
-      this.applyViewerState()
+      // Prevent loop with page / scale application see https://github.com/paperless-ngx/paperless-ngx/issues/13404
+      this.applyViewerState(
+        !!(changes['zoom'] || changes['zoomScale'] || changes['rotation'])
+      )
     }
 
     if (changes['searchQuery']) {
@@ -240,7 +243,7 @@ export class PngxPdfViewerComponent
     }
   }
 
-  private applyViewerState(): void {
+  private applyViewerState(applyScale = true): void {
     if (!this.pdfViewer) {
       return
     }
@@ -264,7 +267,7 @@ export class PngxPdfViewerComponent
     if (this.page === this.lastViewerPage) {
       this.lastViewerPage = undefined
     }
-    if (hasPages) {
+    if (hasPages && applyScale) {
       this.applyScale()
     }
     this.dispatchFindIfReady()

src/documents/mail.py

@@ -36,6 +36,9 @@ def send_email(
 
     TODO: re-evaluate this pending https://code.djangoproject.com/ticket/35581 / https://github.com/django/django/pull/18966
     """
+    if "\r" in subject or "\n" in subject:
+        subject = " ".join(line.strip(" \t") for line in subject.splitlines())
+
     email = EmailMessage(
         subject=subject,
         body=body,

src/documents/management/commands/document_importer.py

@@ -386,10 +386,19 @@ class Command(CryptMixin, PaperlessCommand):
                 raise DeserializationError(
                     f"{model.__name__} has no updatable fields; PK-only models are not supported by the importer",
                 )
+            # MySQL/MariaDB support upserts via ON DUPLICATE KEY UPDATE but,
+            # unlike PostgreSQL/SQLite, cannot target a specific unique field
+            # for the conflict -- passing unique_fields there raises
+            # NotSupportedError.
+            unique_fields = (
+                [model._meta.pk.attname]
+                if connection.features.supports_update_conflicts_with_target
+                else None
+            )
             model.objects.bulk_create(  # type: ignore[attr-defined]
                 instances,
                 update_conflicts=True,
-                unique_fields=[model._meta.pk.attname],
+                unique_fields=unique_fields,
                 update_fields=update_fields,
             )
             loaded_models.add(model)

src/documents/management/commands/document_llmindex.py

@@ -3,6 +3,7 @@ from typing import Any
 from documents.management.commands.base import PaperlessCommand
 from documents.tasks import llmindex_index
 from paperless_ai.indexing import llm_index_compact
+from paperless_ai.indexing import llm_index_migrate
 
 
 class Command(PaperlessCommand):
@@ -13,12 +14,18 @@ class Command(PaperlessCommand):
 
     def add_arguments(self, parser: Any) -> None:
         super().add_arguments(parser)
-        parser.add_argument("command", choices=["rebuild", "update", "compact"])
+        parser.add_argument(
+            "command",
+            choices=["rebuild", "update", "compact", "migrate"],
+        )
 
     def handle(self, *args: Any, **options: Any) -> None:
         if options["command"] == "compact":
             llm_index_compact()
             return
+        if options["command"] == "migrate":
+            llm_index_migrate()
+            return
         llmindex_index(
             rebuild=options["command"] == "rebuild",
             iter_wrapper=lambda docs: self.track(

src/documents/tests/management/test_management_document_llmindex.py

@@ -9,6 +9,7 @@ if TYPE_CHECKING:
 
 _COMPACT = "documents.management.commands.document_llmindex.llm_index_compact"
 _INDEX = "documents.management.commands.document_llmindex.llmindex_index"
+_MIGRATE = "documents.management.commands.document_llmindex.llm_index_migrate"
 
 
 class TestDocumentLlmindexCommand:
@@ -17,6 +18,11 @@ class TestDocumentLlmindexCommand:
         call_command("document_llmindex", "compact")
         mock_compact.assert_called_once_with()
 
+    def test_migrate_calls_llm_index_migrate(self, mocker: MockerFixture) -> None:
+        mock_migrate = mocker.patch(_MIGRATE)
+        call_command("document_llmindex", "migrate")
+        mock_migrate.assert_called_once_with()
+
     def test_rebuild_calls_llmindex_index_with_rebuild_true(
         self,
         mocker: MockerFixture,

src/documents/tests/test_api_email.py

@@ -75,7 +75,7 @@ class TestEmail(DirectoriesMixin, SampleDirMixin, APITestCase):
                 {
                     "documents": [self.doc1.pk, self.doc2.pk],
                     "addresses": "hello@paperless-ngx.com,test@example.com",
-                    "subject": "Bulk email test",
+                    "subject": "Bulk email\n test",
                     "message": "Here are your documents",
                 },
             ),

src/paperless_ai/indexing.py

@@ -144,6 +144,24 @@ def _exclude_readers():
         lock.close()
 
 
+def _with_exclusive_access(operation: str, fn):
+    """Run ``fn()`` with exclusive index access (see ``_exclude_readers()``),
+    for compaction/migration file swaps that must not run while readers are
+    active. Returns ``fn()``'s result, or None (after logging) if active
+    readers do not drain within ``LLM_INDEX_COMPACTION_LOCK_TIMEOUT`` --
+    callers skip the operation this run; it retries next time.
+    """
+    try:
+        with _exclude_readers():
+            return fn()
+    except Timeout:
+        logger.info(
+            "Skipping LLM index %s: index readers are active; will retry next run.",
+            operation,
+        )
+        return None
+
+
 @contextmanager
 def write_store(embed_model_name: str | None = None):
     """Acquire the write lock and yield the vector store.
@@ -168,6 +186,21 @@ def write_store(embed_model_name: str | None = None):
         yield store
 
 
+def _check_and_run_migrations(store: "PaperlessSqliteVecVectorStore") -> bool:
+    """Run any pending structural migrations, returning True if a pending
+    re-embed migration needs the caller to force a rebuild -- never
+    triggered automatically here. Safe to call before any write, including
+    delete()/upsert_document(): has_pending_migration() (see its docstring)
+    keeps this a no-op, with no exclusive access taken, once the store is
+    current.
+    """
+    if not store.has_pending_migration():
+        return False
+    return bool(
+        _with_exclusive_access("migration check", store.check_and_run_migrations),
+    )
+
+
 def _safe_related_name(document: Document, field: str) -> str | None:
     """
     Returns the ``name`` of a related object (correspondent, document_type,
@@ -339,15 +372,7 @@ def update_llm_index(
     happens, since a rebuild always covers the whole library regardless.
     """
     with write_store() as store:
-        try:
-            with _exclude_readers():
-                needs_reembed = store.check_and_run_migrations()
-        except Timeout:
-            logger.info(
-                "Skipping LLM index migration check: index readers are active; "
-                "will retry next run.",
-            )
-            needs_reembed = False
+        needs_reembed = _check_and_run_migrations(store)
         if needs_reembed:
             logger.warning(
                 "LLM index migration requires re-embedding; forcing rebuild.",
@@ -412,14 +437,7 @@ def update_llm_index(
                 else "No changes detected in LLM index."
             )
 
-        try:
-            with _exclude_readers():
-                store.compact()
-        except Timeout:
-            logger.info(
-                "Skipping LLM index compaction: index readers are active; "
-                "will retry next run.",
-            )
+        _with_exclusive_access("compaction", store.compact)
     return msg
 
 
@@ -434,25 +452,60 @@ def llm_index_add_or_update_document(document: Document):
         _embed_nodes(new_nodes, get_embedding_model(config))
 
     with write_store(embed_model_name=get_configured_model_name(config)) as store:
+        needs_reembed = _check_and_run_migrations(store)
+        if needs_reembed:
+            logger.warning(
+                "Skipping incremental LLM index update for document %s: the "
+                "index requires re-embedding first. Run 'document_llmindex "
+                "rebuild' to resolve.",
+                document.id,
+            )
+            return
         store.upsert_document(str(document.id), new_nodes)
 
 
+def llm_index_migrate() -> None:
+    """Apply any pending LLM index schema migrations, with no reindex.
+
+    Intended to run unconditionally on every startup (see the
+    init-llmindex-migrate container step and the bare-metal upgrade docs):
+    has_pending_migration() short-circuits to a metadata-only read once the
+    store is current, so a healthy install pays almost nothing here. Only
+    ever applies structural migrations -- a pending re-embed migration is
+    left for the explicit, deliberate rebuild path (``document_llmindex
+    update``/``rebuild``) to resolve, since re-embedding can be slow and,
+    for a metered embedding backend, cost money.
+    """
+    if not AIConfig().llm_index_enabled:
+        return
+    with write_store() as store:
+        needs_reembed = _check_and_run_migrations(store)
+    if needs_reembed:
+        logger.warning(
+            "LLM index requires re-embedding, which this automatic migration "
+            "check will not do on its own -- it can be slow and, for a "
+            "metered embedding backend, cost money. Run "
+            "'document_llmindex rebuild' manually when ready.",
+        )
+
+
 def llm_index_compact() -> None:
     """Compact the index immediately, rebuilding the table to reclaim space."""
     with write_store() as store:
-        try:
-            with _exclude_readers():
-                store.compact(force=True)
-        except Timeout:
-            logger.info(
-                "Skipping LLM index compaction: index readers are active; "
-                "will retry next run.",
-            )
+        _with_exclusive_access("compaction", lambda: store.compact(force=True))
 
 
 def llm_index_remove_document(document: Document):
     """Remove a document's chunks from the LLM index."""
     with write_store() as store:
+        if _check_and_run_migrations(store):
+            logger.warning(
+                "Skipping removal of document %s from the LLM index: the "
+                "index requires re-embedding first. Run 'document_llmindex "
+                "rebuild' to resolve.",
+                document.id,
+            )
+            return
         store.delete(str(document.id))
 
 

src/paperless_ai/migrations/__init__.py

@@ -0,0 +1,60 @@
+"""Schema migrations for the sqlite-vec vector store.
+
+Each migration lives in its own module here, named ``mNNNN_description.py``
+(e.g. ``m0001_v1_to_v2.py`` -- a leading digit isn't a valid Python
+identifier, hence the ``m`` prefix, unlike Django's own numbered migrations,
+which load via a dynamic ``importlib.import_module()`` call rather than a
+static import statement), and registers itself into ``MIGRATIONS`` at import
+time. ``vector_store.py`` imports those modules at the bottom of the file,
+purely for that registration side effect, after ``PaperlessSqliteVecVectorStore``
+is fully defined -- migrations need it to implement ``apply()`` (see
+``Migration`` below).
+
+To add a new migration: add a new ``mNNNN_description.py`` module here that
+imports ``PaperlessSqliteVecVectorStore`` from ``paperless_ai.vector_store``,
+defines its ``apply()``, and appends a ``Migration`` to ``MIGRATIONS``; then
+import that module at the bottom of ``vector_store.py`` and bump
+``SCHEMA_VERSION`` there. A migration must freeze its own historical DDL for
+any side table its target version depends on (``DROP TABLE IF EXISTS`` +
+its own literal ``CREATE TABLE``/``CREATE INDEX`` statements) rather than
+delegating to any "current schema" helper -- see ``m0001_v1_to_v2.py`` for
+why and the worked example.
+"""
+
+import sqlite3
+from collections.abc import Callable
+from dataclasses import dataclass
+from dataclasses import field
+from typing import Literal
+
+
+@dataclass
+class Migration:
+    """A schema migration for the sqlite-vec vector store.
+
+    kind="structural": rows are copied into a new-schema file with no
+    re-embedding needed.  Supply ``apply(src_conn, dst_conn, dim)``, which
+    must create every table its target schema needs in ``dst_conn`` and copy
+    ``src_conn``'s rows and relevant ``index_meta`` keys into it.
+    ``schema_version`` is written by the migration runner after ``apply``
+    returns, not by ``apply`` itself.
+
+    kind="re-embed": the new schema requires fresh embeddings.
+    ``check_and_run_migrations()`` returns True when it encounters one of
+    these so the caller can force a full rebuild (which recreates the table
+    at the current SCHEMA_VERSION).
+    """
+
+    from_version: int
+    to_version: int
+    kind: Literal["structural", "re-embed"]
+    description: str
+    apply: Callable[[sqlite3.Connection, sqlite3.Connection, int], None] | None = field(
+        default=None,
+        repr=False,
+    )
+
+
+# Registry of all schema migrations in order, populated by each migration
+# module's import-time registration (see the module docstring above).
+MIGRATIONS: list[Migration] = []

src/paperless_ai/tests/test_ai_indexing.py

@@ -1,3 +1,4 @@
+import logging
 from pathlib import Path
 from unittest.mock import MagicMock
 from unittest.mock import patch
@@ -737,6 +738,7 @@ class TestLlmIndexLocking:
         mocker: pytest_mock.MockerFixture,
     ) -> None:
         mock_store = MagicMock()
+        mock_store.has_pending_migration.return_value = False
         mocker.patch(
             "paperless_ai.indexing.write_store",
             return_value=mocker.MagicMock(
@@ -757,12 +759,45 @@ class TestLlmIndexLocking:
 
         mock_store.upsert_document.assert_called_once()
 
+    def test_add_or_update_document_skips_write_when_reembed_pending(
+        self,
+        temp_llm_index_dir: Path,
+        mock_embed_model: FakeEmbedding,
+        mocker: pytest_mock.MockerFixture,
+    ) -> None:
+        """A pending re-embed migration must block the incremental write,
+        not let it proceed against a schema that just changed underneath it.
+        """
+        mock_store = MagicMock()
+        mock_store.has_pending_migration.return_value = True
+        mock_store.check_and_run_migrations.return_value = True
+        mocker.patch(
+            "paperless_ai.indexing.write_store",
+            return_value=mocker.MagicMock(
+                __enter__=mocker.MagicMock(return_value=mock_store),
+                __exit__=mocker.MagicMock(return_value=False),
+            ),
+        )
+        mock_node = MagicMock()
+        mock_node.get_content.return_value = "fake node text"
+        mocker.patch(
+            "paperless_ai.indexing.build_document_node",
+            return_value=[mock_node],
+        )
+
+        doc = MagicMock(spec=Document)
+        doc.id = 1
+        indexing.llm_index_add_or_update_document(doc)
+
+        mock_store.upsert_document.assert_not_called()
+
     def test_remove_document_uses_write_store(
         self,
         temp_llm_index_dir: Path,
         mocker: pytest_mock.MockerFixture,
     ) -> None:
         mock_store = MagicMock()
+        mock_store.has_pending_migration.return_value = False
         mocker.patch(
             "paperless_ai.indexing.write_store",
             return_value=mocker.MagicMock(
@@ -777,6 +812,31 @@ class TestLlmIndexLocking:
 
         mock_store.delete.assert_called_once_with("1")
 
+    def test_remove_document_skips_write_when_reembed_pending(
+        self,
+        temp_llm_index_dir: Path,
+        mocker: pytest_mock.MockerFixture,
+    ) -> None:
+        """A pending re-embed migration must block the delete too, for the
+        same consistency reason as the incremental-update path.
+        """
+        mock_store = MagicMock()
+        mock_store.has_pending_migration.return_value = True
+        mock_store.check_and_run_migrations.return_value = True
+        mocker.patch(
+            "paperless_ai.indexing.write_store",
+            return_value=mocker.MagicMock(
+                __enter__=mocker.MagicMock(return_value=mock_store),
+                __exit__=mocker.MagicMock(return_value=False),
+            ),
+        )
+
+        doc = MagicMock(spec=Document)
+        doc.id = 1
+        indexing.llm_index_remove_document(doc)
+
+        mock_store.delete.assert_not_called()
+
     def test_update_llm_index_rebuild_uses_write_store(
         self,
         temp_llm_index_dir: Path,
@@ -849,6 +909,76 @@ class TestVectorStoreIndexing:
             assert rows >= 1
 
 
+class TestLlmIndexMigrate:
+    def test_noop_when_ai_disabled(self, mocker: pytest_mock.MockerFixture) -> None:
+        """
+        GIVEN:
+            - AI/LLM index support is disabled in configuration
+        WHEN:
+            - llm_index_migrate() is called
+        THEN:
+            - No store is opened and no migration check runs
+        """
+        mocker.patch(
+            "paperless_ai.indexing.AIConfig",
+            return_value=mocker.Mock(llm_index_enabled=False),
+        )
+        write_store_mock = mocker.patch("paperless_ai.indexing.write_store")
+        indexing.llm_index_migrate()
+        write_store_mock.assert_not_called()
+
+    def test_runs_pending_migration_when_enabled(
+        self,
+        mocker: pytest_mock.MockerFixture,
+    ) -> None:
+        """
+        GIVEN:
+            - AI/LLM index support is enabled
+        WHEN:
+            - llm_index_migrate() is called
+        THEN:
+            - The store is opened for write and a migration check runs
+        """
+        mocker.patch(
+            "paperless_ai.indexing.AIConfig",
+            return_value=mocker.Mock(llm_index_enabled=True),
+        )
+        store_mock = mocker.MagicMock()
+        store_mock.has_pending_migration.return_value = False
+        write_store_cm = mocker.patch("paperless_ai.indexing.write_store")
+        write_store_cm.return_value.__enter__.return_value = store_mock
+        indexing.llm_index_migrate()
+        store_mock.has_pending_migration.assert_called_once()
+
+    def test_logs_warning_when_reembed_needed(
+        self,
+        mocker: pytest_mock.MockerFixture,
+        caplog: pytest.LogCaptureFixture,
+    ) -> None:
+        """
+        GIVEN:
+            - AI/LLM index support is enabled
+            - A pending migration requires re-embedding
+        WHEN:
+            - llm_index_migrate() is called
+        THEN:
+            - A warning directs the operator to run a manual rebuild, since
+              this automatic check must never re-embed on its own
+        """
+        mocker.patch(
+            "paperless_ai.indexing.AIConfig",
+            return_value=mocker.Mock(llm_index_enabled=True),
+        )
+        store_mock = mocker.MagicMock()
+        store_mock.has_pending_migration.return_value = True
+        store_mock.check_and_run_migrations.return_value = True
+        write_store_cm = mocker.patch("paperless_ai.indexing.write_store")
+        write_store_cm.return_value.__enter__.return_value = store_mock
+        with caplog.at_level(logging.WARNING, logger="paperless_ai.indexing"):
+            indexing.llm_index_migrate()
+        assert "requires re-embedding" in caplog.text
+
+
 @pytest.mark.django_db
 class TestQuerySimilarDocuments:
     def test_query_similar_documents_respects_allowed_ids(

src/paperless_ai/tests/test_vector_store.py

@@ -9,11 +9,11 @@ from llama_index.core.vector_stores.types import MetadataFilter
 from llama_index.core.vector_stores.types import MetadataFilters
 from llama_index.core.vector_stores.types import VectorStoreQuery
 
+from paperless_ai.migrations import MIGRATIONS
+from paperless_ai.migrations import Migration
 from paperless_ai.vector_store import DB_FILENAME
 from paperless_ai.vector_store import DEFAULT_TABLE_NAME
-from paperless_ai.vector_store import MIGRATIONS
 from paperless_ai.vector_store import SCHEMA_VERSION
-from paperless_ai.vector_store import Migration
 from paperless_ai.vector_store import PaperlessSqliteVecVectorStore
 from paperless_ai.vector_store import _build_where
 
@@ -646,3 +646,50 @@ class TestMigrations:
 
         assert result is True
         assert self._schema_version(store) == 2
+
+    def test_has_pending_migration_false_when_no_table(
+        self,
+        store: PaperlessSqliteVecVectorStore,
+    ) -> None:
+        """
+        GIVEN:
+            - A vector store with no table created yet
+        WHEN:
+            - has_pending_migration() is checked
+        THEN:
+            - False is returned (nothing to migrate before anything exists)
+        """
+        assert store.has_pending_migration() is False
+
+    def test_has_pending_migration_false_at_current_version(
+        self,
+        store: PaperlessSqliteVecVectorStore,
+    ) -> None:
+        """
+        GIVEN:
+            - A store at the current SCHEMA_VERSION
+        WHEN:
+            - has_pending_migration() is checked
+        THEN:
+            - False is returned
+        """
+        store.add([make_node("a1", "1")])
+        assert store.has_pending_migration() is False
+
+    def test_has_pending_migration_true_when_behind(
+        self,
+        store: PaperlessSqliteVecVectorStore,
+    ) -> None:
+        """
+        GIVEN:
+            - A store whose schema_version has been forced behind SCHEMA_VERSION
+        WHEN:
+            - has_pending_migration() is checked
+        THEN:
+            - True is returned
+        """
+        store.add([make_node("a1", "1")])
+        store.client.execute(
+            "UPDATE index_meta SET value = '0' WHERE key = 'schema_version'",
+        )
+        assert store.has_pending_migration() is True

src/paperless_ai/vector_store.py

@@ -2,16 +2,12 @@ import json
 import logging
 import sqlite3
 import struct
-from collections.abc import Callable
 from collections.abc import Iterator
 from collections.abc import Sequence
 from contextlib import contextmanager
-from dataclasses import dataclass
-from dataclasses import field
 from pathlib import Path
 from types import TracebackType
 from typing import Any
-from typing import Literal
 
 import sqlite_vec
 from llama_index.core.bridge.pydantic import PrivateAttr
@@ -26,6 +22,9 @@ from llama_index.core.vector_stores.types import VectorStoreQueryResult
 from llama_index.core.vector_stores.utils import metadata_dict_to_node
 from llama_index.core.vector_stores.utils import node_to_metadata_dict
 
+from paperless_ai.migrations import MIGRATIONS
+from paperless_ai.migrations import Migration
+
 logger = logging.getLogger("paperless_ai.vector_store")
 
 DB_FILENAME = "llmindex.db"
@@ -53,38 +52,6 @@ COMPACT_BATCH_SIZE = 500
 _FILTER_COLUMNS = frozenset({"document_id", "modified"})
 
 
-@dataclass
-class Migration:
-    """A schema migration for the sqlite-vec vector store.
-
-    kind="structural": rows are copied into a new-schema file with no
-    re-embedding needed.  Supply ``apply(src_conn, dst_conn, dim)`` which
-    must create the vec0 table in ``dst_conn``, copy all rows from
-    ``src_conn``, and write ``dim`` / ``embed_model`` / ``total_inserts`` to
-    ``dst_conn``'s ``index_meta``.  ``schema_version`` is written by the
-    migration runner after ``apply`` returns.
-
-    kind="re-embed": the new schema requires fresh embeddings.
-    ``check_and_run_migrations()`` returns True when it encounters one of
-    these so the caller can force a full rebuild (which recreates the table
-    at the current SCHEMA_VERSION).
-    """
-
-    from_version: int
-    to_version: int
-    kind: Literal["structural", "re-embed"]
-    description: str
-    apply: Callable[[sqlite3.Connection, sqlite3.Connection, int], None] | None = field(
-        default=None,
-        repr=False,
-    )
-
-
-# Registry of all schema migrations in order. Empty at v1 -- this is the
-# baseline. Add entries here (and bump SCHEMA_VERSION) when the schema changes.
-MIGRATIONS: list[Migration] = []
-
-
 def _pack(embedding: Sequence[float]) -> bytes:
     return struct.pack(f"{len(embedding)}f", *embedding)
 
@@ -551,6 +518,31 @@ class PaperlessSqliteVecVectorStore(BasePydanticVectorStore):
         Path(compact_path).replace(db_path)
         self._conn = self._open_connection(db_path)
 
+    def _stored_schema_version(self) -> int | None:
+        """The schema_version recorded in index_meta, or None if no table
+        exists. A missing key (a store predating version tracking) is
+        treated as SCHEMA_VERSION -- i.e. already current -- since no
+        migration in MIGRATIONS targets a version before tracking began.
+        """
+        if not self.table_exists():
+            return None
+        raw = self._meta_get("schema_version")
+        return int(raw) if raw is not None else SCHEMA_VERSION
+
+    def has_pending_migration(self) -> bool:
+        """Cheaply check whether a migration is pending, with no exclusive
+        access needed -- just a metadata read under the connection callers
+        already hold via the write FileLock.
+
+        Callers should only pay for check_and_run_migrations()'s exclusive
+        access (a structural migration's file swap must not run while
+        readers are active) when this returns True, so that the common
+        case -- already at SCHEMA_VERSION -- never contends with readers
+        or a concurrent compaction.
+        """
+        current = self._stored_schema_version()
+        return current is not None and current < SCHEMA_VERSION
+
     def check_and_run_migrations(self) -> bool:
         """Apply any pending schema migrations to the store.
 
@@ -559,15 +551,13 @@ class PaperlessSqliteVecVectorStore(BasePydanticVectorStore):
         this method returns True when one is encountered so the caller can
         force a full rebuild (which recreates the table at SCHEMA_VERSION).
 
-        Must be called under the write FileLock.  No-op when the table does
-        not exist or is already at SCHEMA_VERSION.
+        Must be called under the write FileLock, with readers excluded (see
+        has_pending_migration() for a cheap pre-check that avoids paying for
+        that exclusion in the common case).  No-op when the table does not
+        exist or is already at SCHEMA_VERSION.
         """
-        if not self.table_exists():
-            return False
-
-        raw = self._meta_get("schema_version")
-        current = int(raw) if raw is not None else SCHEMA_VERSION
-        if current >= SCHEMA_VERSION:
+        current = self._stored_schema_version()
+        if current is None or current >= SCHEMA_VERSION:
             return False
 
         pending = sorted(
@@ -579,7 +569,7 @@ class PaperlessSqliteVecVectorStore(BasePydanticVectorStore):
             if migration.kind == "re-embed":
                 logger.warning(
                     "LLM index schema v%d -> v%d requires re-embedding (%s); "
-                    "forcing full rebuild.",
+                    "the caller must force a rebuild.",
                     migration.from_version,
                     migration.to_version,
                     migration.description,