perf: optimize SQLite WAL connection pragmas

Author: Algorithm5838

backend/open_webui/internal/db.py

@@ -108,6 +108,23 @@ def _make_async_url(url: str) -> str:
 #              Alembic, peewee migration, health checks)
 # ============================================================
 
+# Shared SQLite connection handler, used by both sync and async engines
+def _sqlite_on_connect(dbapi_connection, connection_record):
+    cursor = dbapi_connection.cursor()
+    if DATABASE_ENABLE_SQLITE_WAL:
+        cursor.execute('PRAGMA journal_mode=WAL')
+        # synchronous=NORMAL is safe with WAL: durable on app crash, may roll back
+        # last transactions on OS crash or power loss; acceptable for most web apps.
+        cursor.execute('PRAGMA synchronous=NORMAL')
+        cursor.execute('PRAGMA journal_size_limit=67108864') # Cap WAL file at 64 MB
+        cursor.execute('PRAGMA cache_size=-32768')           # 32 MB page cache
+        cursor.execute('PRAGMA temp_store=MEMORY')
+        cursor.execute('PRAGMA busy_timeout=5000')           # Retry up to 5 s on lock contention
+    else:
+        cursor.execute('PRAGMA journal_mode=DELETE')
+    cursor.close()
+
+
 # Handle SQLCipher URLs
 if SQLALCHEMY_DATABASE_URL.startswith('sqlite+sqlcipher://'):
     database_password = os.environ.get('DATABASE_PASSWORD')
@@ -154,16 +171,7 @@ def create_sqlcipher_connection():
 
 elif 'sqlite' in SQLALCHEMY_DATABASE_URL:
     engine = create_engine(SQLALCHEMY_DATABASE_URL, connect_args={'check_same_thread': False})
-
-    def on_connect(dbapi_connection, connection_record):
-        cursor = dbapi_connection.cursor()
-        if DATABASE_ENABLE_SQLITE_WAL:
-            cursor.execute('PRAGMA journal_mode=WAL')
-        else:
-            cursor.execute('PRAGMA journal_mode=DELETE')
-        cursor.close()
-
-    event.listen(engine, 'connect', on_connect)
+    event.listen(engine, 'connect', _sqlite_on_connect)
 else:
     if isinstance(DATABASE_POOL_SIZE, int):
         if DATABASE_POOL_SIZE > 0:
@@ -212,14 +220,7 @@ def get_session():
         ASYNC_SQLALCHEMY_DATABASE_URL,
         connect_args={'check_same_thread': False},
     )
-
-    if DATABASE_ENABLE_SQLITE_WAL:
-
-        @event.listens_for(async_engine.sync_engine, 'connect')
-        def _set_sqlite_wal(dbapi_connection, connection_record):
-            cursor = dbapi_connection.cursor()
-            cursor.execute('PRAGMA journal_mode=WAL')
-            cursor.close()
+    event.listen(async_engine.sync_engine, 'connect', _sqlite_on_connect)
 else:
     if isinstance(DATABASE_POOL_SIZE, int):
         if DATABASE_POOL_SIZE > 0: