Simplified storage layer from connection pool to single lazy connection.

config.example.yaml

@@ -49,9 +49,6 @@ owlbot:
   # logs go to stdout only.
   #log_dir: "logs"
 
-  # Maximum number of SQLite connections per module in the connection pool.
-  # Connections are created lazily as needed, up to this limit.
-  pool_size: 4
 
 # Per-module configuration. Each key is a module name (the filename without
 # .py for single-file modules, or the directory name for package modules).

owlbot/api/config.py

@@ -206,20 +206,6 @@ class Config:
             type_fn=float,
         )
 
-    @property
-    def pool_size(self) -> int:
-        """Maximum number of SQLite connections per module storage pool."""
-        return max(
-            1,
-            self._resolve(
-                env="OWLBOT_POOL_SIZE",
-                section="owlbot",
-                key="pool_size",
-                default=4,
-                type_fn=int,
-            ),
-        )
-
     @property
     def command_prefix(self) -> str:
         """Prefix character for chat commands."""

owlbot/api/storage.py

@@ -16,8 +16,6 @@
 
 from __future__ import annotations
 
-import asyncio
-import contextlib
 import contextvars
 import logging
 from contextlib import asynccontextmanager
@@ -35,40 +33,35 @@ class StorageError(Exception):
 
 
 class ModuleStorage:
-    """Module-scoped async SQLite storage backed by a lazy connection pool.
+    """Module-scoped async SQLite storage with a single lazy connection.
 
-    Each module gets its own isolated database file. Connections are created
-    lazily and pooled up to ``pool_size``. WAL mode is enabled so that
-    concurrent readers and a single writer can operate without "database is
-    locked" errors.
+    Each module gets its own isolated database file. The connection is
+    created lazily on the first storage operation and reused for all
+    subsequent calls. WAL mode is enabled for crash resilience.
 
-    Each storage operation (execute, fetch_one, etc.) independently acquires a
-    connection from the pool, auto-commits on success, rolls back on failure,
-    and releases the connection immediately. No connection is held between
-    calls.
+    Each storage operation (execute, fetch_one, etc.) auto-commits on
+    success and rolls back on failure. No transaction state is held
+    between calls.
 
-    For operations that must succeed or fail together, use the transaction()
-    context manager to group them into a single atomic unit.
+    For operations that must succeed or fail together, use the
+    transaction() context manager to group them into a single atomic
+    unit.
     """
 
-    def __init__(self, storage_dir: Path, module_name: str, pool_size: int = 4):
+    def __init__(self, storage_dir: Path, module_name: str):
         """Initialize the storage API.
 
         :param storage_dir: Directory where module databases are stored.
         :param module_name: Name of the module this storage belongs to.
-        :param pool_size: Maximum number of pooled connections.
         """
         self._db_path = storage_dir / f"{module_name}.db"
         self._module_name = module_name
-        self._pool: asyncio.Queue[aiosqlite.Connection] = asyncio.Queue()
-        self._pool_size = pool_size
-        self._all_connections: list[aiosqlite.Connection] = []
+        self._conn: aiosqlite.Connection | None = None
         self._closed = False
         self._txn_conn: contextvars.ContextVar[aiosqlite.Connection | None] = (
             contextvars.ContextVar(f"_txn_conn_{module_name}", default=None)
         )
         self._logger = logging.getLogger(f"owlbot.modules.{module_name}.storage")
-        self._logger.info(f"Database initialized at: {self._db_path.absolute()}")
 
     async def __aenter__(self) -> ModuleStorage:
         """Enter an async context manager that closes the storage on exit.
@@ -91,14 +84,13 @@ class ModuleStorage:
     async def transaction(self) -> AsyncIterator[ModuleStorage]:
         """Context manager for explicit transaction control.
 
-        Use this when you need multiple operations to succeed or fail together.
-        Acquires a dedicated connection from the pool and shares it across all
-        operations within the block. Commits on success, rolls back on exception.
+        Use this when you need multiple operations to succeed or fail
+        together. Shares the single connection across all operations
+        within the block, skipping per-operation auto-commit. Commits on
+        success, rolls back on exception.
 
         Nesting ``transaction()`` calls is not supported and raises
-        ``RuntimeError``.  SQLite only allows one writer at a time, so a
-        nested transaction would deadlock waiting for the outer connection's
-        write lock.
+        ``RuntimeError``.
 
         Example:
             async with ctx.storage.transaction():
@@ -114,7 +106,7 @@ class ModuleStorage:
             raise RuntimeError(
                 "transaction() cannot be nested. Already inside an active transaction."
             )
-        conn = await self._acquire()
+        conn = await self._ensure_connection()
         token = self._txn_conn.set(conn)
         self._logger.debug("Explicit transaction started.")
         try:
@@ -127,7 +119,6 @@ class ModuleStorage:
             raise
         finally:
             self._txn_conn.reset(token)
-            self._release(conn)
 
     async def execute(
         self,
@@ -243,95 +234,46 @@ class ModuleStorage:
             return None
         return row[0]
 
-    async def _create_connection(self) -> aiosqlite.Connection:
-        """Create a new database connection with WAL mode and foreign keys.
-
-        The connection is tracked in ``_all_connections`` immediately after
-        opening so that ``_close()`` can clean it up if the PRAGMA setup is
-        interrupted (e.g. by task cancellation).  A ``busy_timeout`` is set
-        first so that new connections briefly wait for any lock held by a
-        partially-initialised peer instead of failing immediately.
-        """
-        self._db_path.parent.mkdir(parents=True, exist_ok=True)
-        conn = await aiosqlite.connect(self._db_path)
-        # Track immediately so _close() always sees this connection.
-        self._all_connections.append(conn)
-        try:
-            conn.row_factory = aiosqlite.Row
-            await conn.execute("PRAGMA busy_timeout = 1000")
-            await conn.execute("PRAGMA journal_mode = WAL")
-            await conn.execute("PRAGMA foreign_keys = ON")
-        except BaseException:
-            # Setup interrupted (timeout, cancellation, etc.). Close the
-            # connection to release any write lock held by a partially-
-            # executed PRAGMA, then free the pool slot. shield() keeps the
-            # close running on the background thread even if this task is
-            # cancelled; suppress swallows the CancelledError from the await.
-            with contextlib.suppress(ValueError):
-                self._all_connections.remove(conn)
-            with contextlib.suppress(asyncio.CancelledError, Exception):
-                await asyncio.shield(conn.close())
-            raise
-        self._logger.debug(
-            "Pool connection created (%d/%d).",
-            len(self._all_connections),
-            self._pool_size,
-        )
-        return conn
-
-    async def _acquire(self) -> aiosqlite.Connection:
-        """Acquire a connection from the pool, creating one if needed."""
+    async def _ensure_connection(self) -> aiosqlite.Connection:
+        """Return the existing connection or create one on first use."""
         if self._closed:
             raise StorageError("Storage is closed")
-
-        try:
-            return self._pool.get_nowait()
-        except asyncio.QueueEmpty:
-            pass
-
-        if len(self._all_connections) < self._pool_size:
-            return await self._create_connection()
-
-        # Pool exhausted, wait for one to be returned.
-        return await self._pool.get()
-
-    def _release(self, conn: aiosqlite.Connection) -> None:
-        """Return a connection to the pool."""
-        self._pool.put_nowait(conn)
+        if self._conn is not None:
+            return self._conn
+        self._db_path.parent.mkdir(parents=True, exist_ok=True)
+        conn = await aiosqlite.connect(self._db_path)
+        conn.row_factory = aiosqlite.Row
+        await conn.execute("PRAGMA journal_mode = WAL")
+        await conn.execute("PRAGMA foreign_keys = ON")
+        self._conn = conn
+        self._logger.info(f"Database opened at: {self._db_path.absolute()}")
+        return conn
 
     @asynccontextmanager
     async def _connection(self) -> AsyncIterator[aiosqlite.Connection]:
-        """Async context manager that provides a connection.
+        """Async context manager that provides the connection.
 
         If already inside a ``transaction()``, yields the shared connection
         without committing (the transaction block handles that). Otherwise
-        acquires a standalone connection from the pool that auto-commits on
-        success and rolls back on failure before being released.
+        auto-commits on success and rolls back on failure.
         """
         existing = self._txn_conn.get()
         if existing is not None:
             yield existing
             return
 
-        conn = await self._acquire()
+        conn = await self._ensure_connection()
         try:
             yield conn
             await conn.commit()
         except BaseException:
             await conn.rollback()
             raise
-        finally:
-            self._release(conn)
 
     async def _close(self) -> None:
-        """Close all pool connections (internal use by bot)."""
+        """Close the connection (internal use by bot)."""
         self._closed = True
-
-        for conn in self._all_connections:
-            await conn.close()
-
-        while not self._pool.empty():
-            self._pool.get_nowait()
-
-        self._all_connections.clear()
-        self._logger.info("All pool connections closed.")
+        if self._conn is not None:
+            await self._conn.close()
+            self._conn = None
+        self._logger.info("Connection closed.")

owlbot/module_loader.py

@@ -320,9 +320,7 @@ class ModuleLoader:
             module_templates = ModuleTemplates(module_dir, self._core_template_dir)
 
             scoped_config = ModuleConfig(self.config, module_name)
-            storage = ModuleStorage(
-                self.config.storage_dir, module_name, self.config.pool_size
-            )
+            storage = ModuleStorage(self.config.storage_dir, module_name)
             module_commands = ModuleCommands(self.command_dispatcher, module_name)
             module_events = ModuleEvents(self.event_dispatcher, module_name)
             module_routes = ModuleRoutes(

tests/test_storage.py

@@ -39,18 +39,18 @@ async def storage_with_table(storage: ModuleStorage) -> ModuleStorage:
 
 
 class TestLazyConnections:
-    """No connections exist until the first operation."""
+    """No connection exists until the first operation."""
 
-    async def test_no_connections_before_use(self, storage: ModuleStorage) -> None:
-        """Pool is empty immediately after construction."""
-        assert len(storage._all_connections) == 0
+    async def test_no_connection_before_use(self, storage: ModuleStorage) -> None:
+        """Connection is None immediately after construction."""
+        assert storage._conn is None
 
-    async def test_first_operation_creates_one_connection(
+    async def test_first_operation_creates_connection(
         self, storage: ModuleStorage
     ) -> None:
-        """The first execute creates exactly one pooled connection."""
+        """The first execute creates the connection."""
         await storage.execute("SELECT 1")
-        assert len(storage._all_connections) == 1
+        assert storage._conn is not None
 
 
 class TestPragmas:
@@ -196,17 +196,15 @@ class TestAutoCommit:
     async def test_auto_commits_on_success(
         self, storage_with_table: ModuleStorage
     ) -> None:
-        """A successful write is visible from a second storage instance."""
+        """A successful write is visible on the next read."""
         await storage_with_table.execute(
             "INSERT INTO items (name, value) VALUES (?, ?)", ("a", 1)
         )
-        # Open a second storage pointing at the same file to verify commit.
-        async with ModuleStorage(
-            storage_with_table._db_path.parent, "test_module"
-        ) as s2:
-            row = await s2.fetch_one("SELECT name FROM items WHERE id = 1")
-            assert row is not None
-            assert row["name"] == "a"
+        row = await storage_with_table.fetch_one(
+            "SELECT name FROM items WHERE id = 1"
+        )
+        assert row is not None
+        assert row["name"] == "a"
 
     async def test_auto_rollback_on_error(
         self, storage_with_table: ModuleStorage
@@ -267,21 +265,6 @@ class TestTransaction:
                 async with storage_with_table.transaction():
                     pass  # pragma: no cover
 
-    async def test_uncommitted_transaction_invisible_from_other_connection(
-        self, storage_with_table: ModuleStorage
-    ) -> None:
-        """Uncommitted writes inside a transaction are not visible externally."""
-        async with (
-            ModuleStorage(storage_with_table._db_path.parent, "test_module") as s2,
-            storage_with_table.transaction(),
-        ):
-            await storage_with_table.execute(
-                "INSERT INTO items (name, value) VALUES (?, ?)", ("a", 1)
-            )
-            # Before commit, s2 should not see the row.
-            row = await s2.fetch_one("SELECT name FROM items WHERE id = 1")
-            assert row is None
-
     async def test_rolls_back_on_cancellation(
         self, storage_with_table: ModuleStorage
     ) -> None:
@@ -304,48 +287,6 @@ class TestTransaction:
         assert row is None
 
 
-class TestConnectionPool:
-    """Connection pool reuses connections and respects pool_size."""
-
-    async def test_connections_are_reused(self, storage: ModuleStorage) -> None:
-        """After release, the same connection is reused."""
-        await storage.execute("SELECT 1")
-        assert len(storage._all_connections) == 1
-        await storage.execute("SELECT 2")
-        assert len(storage._all_connections) == 1
-
-    async def test_pool_grows_up_to_pool_size(self, tmp_path: Path) -> None:
-        """Concurrent transactions grow the pool up to pool_size."""
-        gate = asyncio.Event()
-
-        async def hold_transaction(storage: ModuleStorage) -> None:
-            async with storage.transaction():
-                gate.set()
-                await asyncio.sleep(0.5)
-
-        async with ModuleStorage(tmp_path, "pool_test", pool_size=2) as s:
-            task = asyncio.create_task(hold_transaction(s))
-            await gate.wait()
-            # First task holds one connection; acquire a second directly.
-            conn = await asyncio.wait_for(s._acquire(), timeout=1.0)
-            assert len(s._all_connections) == 2
-            s._release(conn)
-            task.cancel()
-            with contextlib.suppress(asyncio.CancelledError):
-                await task
-
-    async def test_pool_exhaustion_blocks(self, tmp_path: Path) -> None:
-        """When the pool is exhausted, acquire blocks until a connection is released."""
-        async with (
-            ModuleStorage(tmp_path, "pool_block", pool_size=1) as s,
-            s.transaction(),
-        ):
-            # Pool is exhausted (pool_size=1, one held by transaction).
-            # A second acquire should block, so wait_for should time out.
-            with pytest.raises(TimeoutError):
-                await asyncio.wait_for(s._acquire(), timeout=0.1)
-
-
 class TestStorageError:
     """Invalid SQL raises StorageError wrapping the underlying error."""
 
@@ -412,15 +353,15 @@ class TestStorageError:
 
 
 class TestClose:
-    """_close() drains the pool and marks storage closed."""
+    """_close() closes the connection and marks storage closed."""
 
-    async def test_close_drains_pool(self, storage: ModuleStorage) -> None:
-        """After close, all connections are removed."""
+    async def test_close_releases_connection(self, storage: ModuleStorage) -> None:
+        """After close, the connection is None."""
         await storage.execute("SELECT 1")
-        assert len(storage._all_connections) == 1
+        assert storage._conn is not None
         await storage._close()
-        assert len(storage._all_connections) == 0
-        assert storage._closed is True
+        assert storage._closed
+        assert storage._conn is None
 
     async def test_double_close_is_safe(self, storage: ModuleStorage) -> None:
         """Calling _close() twice does not raise."""
@@ -429,9 +370,9 @@ class TestClose:
         await storage._close()
 
     async def test_context_manager_closes_on_exit(self, tmp_path: Path) -> None:
-        """Exiting the async with block closes all connections."""
+        """Exiting the async with block closes the connection."""
         async with ModuleStorage(tmp_path, "ctx_test") as s:
             await s.execute("SELECT 1")
-            assert len(s._all_connections) == 1
-        assert len(s._all_connections) == 0
-        assert s._closed is True
+            assert s._conn is not None
+        assert s._closed
+        assert s._conn is None