perf(db): set the SQLite pragmas from a connect hook and clear WAL sidecars on db reset

backend/database/session.py

@@ -1,10 +1,9 @@
 """Engine creation, initialization, and session management."""
 
 import logging
-import sqlite3 as _sqlite3
 import uuid
 
-from sqlalchemy import create_engine
+from sqlalchemy import create_engine, event
 from sqlalchemy.orm import sessionmaker
 
 from .. import config
@@ -23,21 +22,6 @@ from .seed import backfill_generation_versions, seed_builtin_presets
 logger = logging.getLogger(__name__)
 
 
-def _make_connection(db_path: str) -> _sqlite3.Connection:
-    """Open a SQLite connection with WAL journal mode and a 5-second busy timeout.
-
-    WAL allows concurrent readers while a write is in progress (the default
-    DELETE journal blocks all readers).  This matters for voicebox because SSE
-    status polls and history queries run concurrently with the generation worker
-    writing to the same database.  The busy timeout prevents "database is
-    locked" errors when two writers briefly contend on the same write slot.
-    """
-    conn = _sqlite3.connect(db_path, check_same_thread=False)
-    conn.execute("PRAGMA journal_mode=WAL")
-    conn.execute("PRAGMA busy_timeout=5000")
-    return conn
-
-
 # Initialized by init_db()
 engine = None
 SessionLocal = None
@@ -54,15 +38,21 @@ def init_db() -> None:
     engine = create_engine(
         f"sqlite:///{_db_path}",
         connect_args={"check_same_thread": False},
-        # Each connection enables WAL journal mode and sets a 5-second busy
-        # timeout.  WAL allows concurrent readers during a write (the default
-        # DELETE/ROLLBACK journal blocks all readers), which matters for
-        # voicebox because SSE status polls and history queries run
+    )
+
+    @event.listens_for(engine, "connect")
+    def _set_sqlite_pragmas(dbapi_connection, _record) -> None:
+        # Each pooled connection enables WAL journal mode and sets a 5-second
+        # busy timeout.  WAL allows concurrent readers during a write (the
+        # default DELETE/ROLLBACK journal blocks all readers), which matters
+        # for voicebox because SSE status polls and history queries run
         # concurrently with the generation worker writing to the same db.
         # busy_timeout prevents "database is locked" errors when two
         # connections briefly contend on the same write slot.
-        creator=lambda: _make_connection(str(_db_path)),
-    )
+        cursor = dbapi_connection.cursor()
+        cursor.execute("PRAGMA journal_mode=WAL")
+        cursor.execute("PRAGMA busy_timeout=5000")
+        cursor.close()
 
     SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)