# sqlalchemy/pool.py # Copyright (C) 2005-2013 the SQLAlchemy authors and contributors # # This module is part of SQLAlchemy and is released under # the MIT License: http://www.opensource.org/licenses/mit-license.php """Connection pooling for DB-API connections. Provides a number of connection pool implementations for a variety of usage scenarios and thread behavior requirements imposed by the application, DB-API or database itself. Also provides a DB-API 2.0 connection proxying mechanism allowing regular DB-API connect() methods to be transparently managed by a SQLAlchemy connection pool. """ import time import traceback import weakref from . import exc, log, event, events, interfaces, util from .util import queue as sqla_queue from .util import threading, memoized_property, \ chop_traceback proxies = {} def manage(module, **params): """Return a proxy for a DB-API module that automatically pools connections. Given a DB-API 2.0 module and pool management parameters, returns a proxy for the module that will automatically pool connections, creating new connection pools for each distinct set of connection arguments sent to the decorated module's connect() function. :param module: a DB-API 2.0 database module :param poolclass: the class used by the pool module to provide pooling. Defaults to :class:`.QueuePool`. :param \*\*params: will be passed through to *poolclass* """ try: return proxies[module] except KeyError: return proxies.setdefault(module, _DBProxy(module, **params)) def clear_managers(): """Remove all current DB-API 2.0 managers. All pools and connections are disposed. """ for manager in proxies.itervalues(): manager.close() proxies.clear() reset_rollback = util.symbol('reset_rollback') reset_commit = util.symbol('reset_commit') reset_none = util.symbol('reset_none') class _ConnDialect(object): """partial implementation of :class:`.Dialect` which provides DBAPI connection methods. When a :class:`.Pool` is combined with an :class:`.Engine`, the :class:`.Engine` replaces this with its own :class:`.Dialect`. """ def do_rollback(self, dbapi_connection): dbapi_connection.rollback() def do_commit(self, dbapi_connection): dbapi_connection.commit() def do_close(self, dbapi_connection): dbapi_connection.close() class Pool(log.Identified): """Abstract base class for connection pools.""" _dialect = _ConnDialect() def __init__(self, creator, recycle=-1, echo=None, use_threadlocal=False, logging_name=None, reset_on_return=True, listeners=None, events=None, _dispatch=None, _dialect=None): """ Construct a Pool. :param creator: a callable function that returns a DB-API connection object. The function will be called with parameters. :param recycle: If set to non -1, number of seconds between connection recycling, which means upon checkout, if this timeout is surpassed the connection will be closed and replaced with a newly opened connection. Defaults to -1. :param logging_name: String identifier which will be used within the "name" field of logging records generated within the "sqlalchemy.pool" logger. Defaults to a hexstring of the object's id. :param echo: If True, connections being pulled and retrieved from the pool will be logged to the standard output, as well as pool sizing information. Echoing can also be achieved by enabling logging for the "sqlalchemy.pool" namespace. Defaults to False. :param use_threadlocal: If set to True, repeated calls to :meth:`connect` within the same application thread will be guaranteed to return the same connection object, if one has already been retrieved from the pool and has not been returned yet. Offers a slight performance advantage at the cost of individual transactions by default. The :meth:`unique_connection` method is provided to bypass the threadlocal behavior installed into :meth:`connect`. :param reset_on_return: Configures the action to take on connections as they are returned to the pool. See the argument description in :class:`.QueuePool` for more detail. :param events: a list of 2-tuples, each of the form ``(callable, target)`` which will be passed to event.listen() upon construction. Provided here so that event listeners can be assigned via ``create_engine`` before dialect-level listeners are applied. :param listeners: Deprecated. A list of :class:`~sqlalchemy.interfaces.PoolListener`-like objects or dictionaries of callables that receive events when DB-API connections are created, checked out and checked in to the pool. This has been superseded by :func:`~sqlalchemy.event.listen`. """ if logging_name: self.logging_name = self._orig_logging_name = logging_name else: self._orig_logging_name = None log.instance_logger(self, echoflag=echo) self._threadconns = threading.local() self._creator = creator self._recycle = recycle self._use_threadlocal = use_threadlocal if reset_on_return in ('rollback', True, reset_rollback): self._reset_on_return = reset_rollback elif reset_on_return in (None, False, reset_none): self._reset_on_return = reset_none elif reset_on_return in ('commit', reset_commit): self._reset_on_return = reset_commit else: raise exc.ArgumentError( "Invalid value for 'reset_on_return': %r" % reset_on_return) self.echo = echo if _dispatch: self.dispatch._update(_dispatch, only_propagate=False) if _dialect: self._dialect = _dialect if events: for fn, target in events: event.listen(self, target, fn) if listeners: util.warn_deprecated( "The 'listeners' argument to Pool (and " "create_engine()) is deprecated. Use event.listen().") for l in listeners: self.add_listener(l) dispatch = event.dispatcher(events.PoolEvents) def _close_connection(self, connection): self.logger.debug("Closing connection %r", connection) try: self._dialect.do_close(connection) except (SystemExit, KeyboardInterrupt): raise except: self.logger.debug("Exception closing connection %r", connection) @util.deprecated( 2.7, "Pool.add_listener is deprecated. Use event.listen()") def add_listener(self, listener): """Add a :class:`.PoolListener`-like object to this pool. ``listener`` may be an object that implements some or all of PoolListener, or a dictionary of callables containing implementations of some or all of the named methods in PoolListener. """ interfaces.PoolListener._adapt_listener(self, listener) def unique_connection(self): """Produce a DBAPI connection that is not referenced by any thread-local context. This method is different from :meth:`.Pool.connect` only if the ``use_threadlocal`` flag has been set to ``True``. """ return _ConnectionFairy(self).checkout() def _create_connection(self): """Called by subclasses to create a new ConnectionRecord.""" return _ConnectionRecord(self) def recreate(self): """Return a new :class:`.Pool`, of the same class as this one and configured with identical creation arguments. This method is used in conjunection with :meth:`dispose` to close out an entire :class:`.Pool` and create a new one in its place. """ raise NotImplementedError() def dispose(self): """Dispose of this pool. This method leaves the possibility of checked-out connections remaining open, as it only affects connections that are idle in the pool. See also the :meth:`Pool.recreate` method. """ raise NotImplementedError() def _replace(self): """Dispose + recreate this pool. Subclasses may employ special logic to move threads waiting on this pool to the new one. """ self.dispose() return self.recreate() def connect(self): """Return a DBAPI connection from the pool. The connection is instrumented such that when its ``close()`` method is called, the connection will be returned to the pool. """ if not self._use_threadlocal: return _ConnectionFairy(self).checkout() try: rec = self._threadconns.current() if rec: return rec.checkout() except AttributeError: pass agent = _ConnectionFairy(self) self._threadconns.current = weakref.ref(agent) return agent.checkout() def _return_conn(self, record): """Given a _ConnectionRecord, return it to the :class:`.Pool`. This method is called when an instrumented DBAPI connection has its ``close()`` method called. """ if self._use_threadlocal: try: del self._threadconns.current except AttributeError: pass self._do_return_conn(record) def _do_get(self): """Implementation for :meth:`get`, supplied by subclasses.""" raise NotImplementedError() def _do_return_conn(self, conn): """Implementation for :meth:`return_conn`, supplied by subclasses.""" raise NotImplementedError() def status(self): raise NotImplementedError() class _ConnectionRecord(object): finalize_callback = None def __init__(self, pool): self.__pool = pool self.connection = self.__connect() pool.dispatch.first_connect.\ for_modify(pool.dispatch).\ exec_once(self.connection, self) pool.dispatch.connect(self.connection, self) @util.memoized_property def info(self): return {} def close(self): if self.connection is not None: self.__pool._close_connection(self.connection) def invalidate(self, e=None): if e is not None: self.__pool.logger.info( "Invalidate connection %r (reason: %s:%s)", self.connection, e.__class__.__name__, e) else: self.__pool.logger.info( "Invalidate connection %r", self.connection) self.__close() self.connection = None def get_connection(self): if self.connection is None: self.connection = self.__connect() self.info.clear() if self.__pool.dispatch.connect: self.__pool.dispatch.connect(self.connection, self) elif self.__pool._recycle > -1 and \ time.time() - self.starttime > self.__pool._recycle: self.__pool.logger.info( "Connection %r exceeded timeout; recycling", self.connection) self.__close() self.connection = self.__connect() self.info.clear() if self.__pool.dispatch.connect: self.__pool.dispatch.connect(self.connection, self) return self.connection def checkin(self): self.fairy = None connection = self.connection pool = self.__pool if self.finalize_callback: self.finalize_callback(connection) del self.finalize_callback if pool.dispatch.checkin: pool.dispatch.checkin(connection, self) pool._return_conn(self) def __close(self): self.__pool._close_connection(self.connection) def __connect(self): try: self.starttime = time.time() connection = self.__pool._creator() self.__pool.logger.debug("Created new connection %r", connection) return connection except Exception, e: self.__pool.logger.debug("Error on connect(): %s", e) raise def _finalize_fairy(connection, connection_record, pool, ref, echo): _refs.discard(connection_record) if ref is not None and \ connection_record.fairy is not ref: return if connection_record and echo: pool.logger.debug("Connection %r being returned to pool", connection) if connection is not None: try: if pool.dispatch.reset: pool.dispatch.reset(connection, connection_record) if pool._reset_on_return is reset_rollback: pool._dialect.do_rollback(connection) elif pool._reset_on_return is reset_commit: pool._dialect.do_commit(connection) # Immediately close detached instances if connection_record is None: pool._close_connection(connection) except Exception, e: if connection_record is not None: connection_record.invalidate(e=e) if isinstance(e, (SystemExit, KeyboardInterrupt)): raise if connection_record: connection_record.checkin() _refs = set() class _ConnectionFairy(object): """Proxies a DB-API connection and provides return-on-dereference support.""" def __init__(self, pool): self._pool = pool self.__counter = 0 self._echo = _echo = pool._should_log_debug() try: rec = self._connection_record = pool._do_get() try: conn = self.connection = self._connection_record.get_connection() except: self._connection_record.checkin() raise rec.fairy = weakref.ref( self, lambda ref: _finalize_fairy and \ _finalize_fairy(conn, rec, pool, ref, _echo) ) _refs.add(rec) except: # helps with endless __getattr__ loops later on self.connection = None self._connection_record = None raise if self._echo: self._pool.logger.debug("Connection %r checked out from pool" % self.connection) @property def _logger(self): return self._pool.logger @property def is_valid(self): return self.connection is not None @util.memoized_property def info(self): """Info dictionary associated with the underlying DBAPI connection referred to by this :class:`.ConnectionFairy`, allowing user-defined data to be associated with the connection. The data here will follow along with the DBAPI connection including after it is returned to the connection pool and used again in subsequent instances of :class:`.ConnectionFairy`. """ try: return self._connection_record.info except AttributeError: raise exc.InvalidRequestError("This connection is closed") def invalidate(self, e=None): """Mark this connection as invalidated. The connection will be immediately closed. The containing ConnectionRecord will create a new connection when next used. """ if self.connection is None: raise exc.InvalidRequestError("This connection is closed") if self._connection_record is not None: self._connection_record.invalidate(e=e) self.connection = None self._close() def cursor(self, *args, **kwargs): return self.connection.cursor(*args, **kwargs) def __getattr__(self, key): return getattr(self.connection, key) def checkout(self): if self.connection is None: raise exc.InvalidRequestError("This connection is closed") self.__counter += 1 if not self._pool.dispatch.checkout or self.__counter != 1: return self # Pool listeners can trigger a reconnection on checkout attempts = 2 while attempts > 0: try: self._pool.dispatch.checkout(self.connection, self._connection_record, self) return self except exc.DisconnectionError, e: self._pool.logger.info( "Disconnection detected on checkout: %s", e) self._connection_record.invalidate(e) self.connection = self._connection_record.get_connection() attempts -= 1 self._pool.logger.info("Reconnection attempts exhausted on checkout") self.invalidate() raise exc.InvalidRequestError("This connection is closed") def detach(self): """Separate this connection from its Pool. This means that the connection will no longer be returned to the pool when closed, and will instead be literally closed. The containing ConnectionRecord is separated from the DB-API connection, and will create a new connection when next used. Note that any overall connection limiting constraints imposed by a Pool implementation may be violated after a detach, as the detached connection is removed from the pool's knowledge and control. """ if self._connection_record is not None: _refs.remove(self._connection_record) self._connection_record.fairy = None self._connection_record.connection = None self._pool._do_return_conn(self._connection_record) self.info = self.info.copy() self._connection_record = None def close(self): self.__counter -= 1 if self.__counter == 0: self._close() def _close(self): _finalize_fairy(self.connection, self._connection_record, self._pool, None, self._echo) self.connection = None self._connection_record = None class SingletonThreadPool(Pool): """A Pool that maintains one connection per thread. Maintains one connection per each thread, never moving a connection to a thread other than the one which it was created in. Options are the same as those of :class:`.Pool`, as well as: :param pool_size: The number of threads in which to maintain connections at once. Defaults to five. :class:`.SingletonThreadPool` is used by the SQLite dialect automatically when a memory-based database is used. See :ref:`sqlite_toplevel`. """ def __init__(self, creator, pool_size=5, **kw): kw['use_threadlocal'] = True Pool.__init__(self, creator, **kw) self._conn = threading.local() self._all_conns = set() self.size = pool_size def recreate(self): self.logger.info("Pool recreating") return self.__class__(self._creator, pool_size=self.size, recycle=self._recycle, echo=self.echo, logging_name=self._orig_logging_name, use_threadlocal=self._use_threadlocal, reset_on_return=self._reset_on_return, _dispatch=self.dispatch, _dialect=self._dialect) def dispose(self): """Dispose of this pool.""" for conn in self._all_conns: try: conn.close() except (SystemExit, KeyboardInterrupt): raise except: # pysqlite won't even let you close a conn from a thread # that didn't create it pass self._all_conns.clear() def _cleanup(self): while len(self._all_conns) > self.size: c = self._all_conns.pop() c.close() def status(self): return "SingletonThreadPool id:%d size: %d" % \ (id(self), len(self._all_conns)) def _do_return_conn(self, conn): pass def _do_get(self): try: c = self._conn.current() if c: return c except AttributeError: pass c = self._create_connection() self._conn.current = weakref.ref(c) self._all_conns.add(c) if len(self._all_conns) > self.size: self._cleanup() return c class DummyLock(object): def acquire(self, wait=True): return True def release(self): pass class QueuePool(Pool): """A :class:`.Pool` that imposes a limit on the number of open connections. :class:`.QueuePool` is the default pooling implementation used for all :class:`.Engine` objects, unless the SQLite dialect is in use. """ def __init__(self, creator, pool_size=5, max_overflow=10, timeout=30, **kw): """ Construct a QueuePool. :param creator: a callable function that returns a DB-API connection object. The function will be called with parameters. :param pool_size: The size of the pool to be maintained, defaults to 5. This is the largest number of connections that will be kept persistently in the pool. Note that the pool begins with no connections; once this number of connections is requested, that number of connections will remain. ``pool_size`` can be set to 0 to indicate no size limit; to disable pooling, use a :class:`~sqlalchemy.pool.NullPool` instead. :param max_overflow: The maximum overflow size of the pool. When the number of checked-out connections reaches the size set in pool_size, additional connections will be returned up to this limit. When those additional connections are returned to the pool, they are disconnected and discarded. It follows then that the total number of simultaneous connections the pool will allow is pool_size + `max_overflow`, and the total number of "sleeping" connections the pool will allow is pool_size. `max_overflow` can be set to -1 to indicate no overflow limit; no limit will be placed on the total number of concurrent connections. Defaults to 10. :param timeout: The number of seconds to wait before giving up on returning a connection. Defaults to 30. :param recycle: If set to non -1, number of seconds between connection recycling, which means upon checkout, if this timeout is surpassed the connection will be closed and replaced with a newly opened connection. Defaults to -1. :param echo: If True, connections being pulled and retrieved from the pool will be logged to the standard output, as well as pool sizing information. Echoing can also be achieved by enabling logging for the "sqlalchemy.pool" namespace. Defaults to False. :param use_threadlocal: If set to True, repeated calls to :meth:`connect` within the same application thread will be guaranteed to return the same connection object, if one has already been retrieved from the pool and has not been returned yet. Offers a slight performance advantage at the cost of individual transactions by default. The :meth:`unique_connection` method is provided to bypass the threadlocal behavior installed into :meth:`connect`. :param reset_on_return: Determine steps to take on connections as they are returned to the pool. reset_on_return can have any of these values: * 'rollback' - call rollback() on the connection, to release locks and transaction resources. This is the default value. The vast majority of use cases should leave this value set. * True - same as 'rollback', this is here for backwards compatibility. * 'commit' - call commit() on the connection, to release locks and transaction resources. A commit here may be desirable for databases that cache query plans if a commit is emitted, such as Microsoft SQL Server. However, this value is more dangerous than 'rollback' because any data changes present on the transaction are committed unconditionally. * None - don't do anything on the connection. This setting should only be made on a database that has no transaction support at all, namely MySQL MyISAM. By not doing anything, performance can be improved. This setting should **never be selected** for a database that supports transactions, as it will lead to deadlocks and stale state. * False - same as None, this is here for backwards compatibility. .. versionchanged:: 0.7.6 ``reset_on_return`` accepts values. :param listeners: A list of :class:`~sqlalchemy.interfaces.PoolListener`-like objects or dictionaries of callables that receive events when DB-API connections are created, checked out and checked in to the pool. """ Pool.__init__(self, creator, **kw) self._pool = sqla_queue.Queue(pool_size) self._overflow = 0 - pool_size self._max_overflow = max_overflow self._timeout = timeout self._overflow_lock = threading.Lock() if self._max_overflow > -1 \ else DummyLock() def _do_return_conn(self, conn): try: self._pool.put(conn, False) except sqla_queue.Full: conn.close() self._overflow_lock.acquire() try: self._overflow -= 1 finally: self._overflow_lock.release() def _do_get(self): try: wait = self._max_overflow > -1 and \ self._overflow >= self._max_overflow return self._pool.get(wait, self._timeout) except sqla_queue.SAAbort, aborted: return aborted.context._do_get() except sqla_queue.Empty: if self._max_overflow > -1 and \ self._overflow >= self._max_overflow: if not wait: return self._do_get() else: raise exc.TimeoutError( "QueuePool limit of size %d overflow %d reached, " "connection timed out, timeout %d" % (self.size(), self.overflow(), self._timeout)) self._overflow_lock.acquire() try: if self._max_overflow > -1 and \ self._overflow >= self._max_overflow: return self._do_get() else: con = self._create_connection() self._overflow += 1 return con finally: self._overflow_lock.release() def recreate(self): self.logger.info("Pool recreating") return self.__class__(self._creator, pool_size=self._pool.maxsize, max_overflow=self._max_overflow, timeout=self._timeout, recycle=self._recycle, echo=self.echo, logging_name=self._orig_logging_name, use_threadlocal=self._use_threadlocal, reset_on_return=self._reset_on_return, _dispatch=self.dispatch, _dialect=self._dialect) def dispose(self): while True: try: conn = self._pool.get(False) conn.close() except sqla_queue.Empty: break self._overflow = 0 - self.size() self.logger.info("Pool disposed. %s", self.status()) def _replace(self): self.dispose() np = self.recreate() self._pool.abort(np) return np def status(self): return "Pool size: %d Connections in pool: %d "\ "Current Overflow: %d Current Checked out "\ "connections: %d" % (self.size(), self.checkedin(), self.overflow(), self.checkedout()) def size(self): return self._pool.maxsize def checkedin(self): return self._pool.qsize() def overflow(self): return self._overflow def checkedout(self): return self._pool.maxsize - self._pool.qsize() + self._overflow class NullPool(Pool): """A Pool which does not pool connections. Instead it literally opens and closes the underlying DB-API connection per each connection open/close. Reconnect-related functions such as ``recycle`` and connection invalidation are not supported by this Pool implementation, since no connections are held persistently. .. versionchanged:: 0.7 :class:`.NullPool` is used by the SQlite dialect automatically when a file-based database is used. See :ref:`sqlite_toplevel`. """ def status(self): return "NullPool" def _do_return_conn(self, conn): conn.close() def _do_get(self): return self._create_connection() def recreate(self): self.logger.info("Pool recreating") return self.__class__(self._creator, recycle=self._recycle, echo=self.echo, logging_name=self._orig_logging_name, use_threadlocal=self._use_threadlocal, reset_on_return=self._reset_on_return, _dispatch=self.dispatch, _dialect=self._dialect) def dispose(self): pass class StaticPool(Pool): """A Pool of exactly one connection, used for all requests. Reconnect-related functions such as ``recycle`` and connection invalidation (which is also used to support auto-reconnect) are not currently supported by this Pool implementation but may be implemented in a future release. """ @memoized_property def _conn(self): return self._creator() @memoized_property def connection(self): return _ConnectionRecord(self) def status(self): return "StaticPool" def dispose(self): if '_conn' in self.__dict__: self._conn.close() self._conn = None def recreate(self): self.logger.info("Pool recreating") return self.__class__(creator=self._creator, recycle=self._recycle, use_threadlocal=self._use_threadlocal, reset_on_return=self._reset_on_return, echo=self.echo, logging_name=self._orig_logging_name, _dispatch=self.dispatch, _dialect=self._dialect) def _create_connection(self): return self._conn def _do_return_conn(self, conn): pass def _do_get(self): return self.connection class AssertionPool(Pool): """A :class:`.Pool` that allows at most one checked out connection at any given time. This will raise an exception if more than one connection is checked out at a time. Useful for debugging code that is using more connections than desired. .. versionchanged:: 0.7 :class:`.AssertionPool` also logs a traceback of where the original connection was checked out, and reports this in the assertion error raised. """ def __init__(self, *args, **kw): self._conn = None self._checked_out = False self._store_traceback = kw.pop('store_traceback', True) self._checkout_traceback = None Pool.__init__(self, *args, **kw) def status(self): return "AssertionPool" def _do_return_conn(self, conn): if not self._checked_out: raise AssertionError("connection is not checked out") self._checked_out = False assert conn is self._conn def dispose(self): self._checked_out = False if self._conn: self._conn.close() def recreate(self): self.logger.info("Pool recreating") return self.__class__(self._creator, echo=self.echo, logging_name=self._orig_logging_name, _dispatch=self.dispatch, _dialect=self._dialect) def _do_get(self): if self._checked_out: if self._checkout_traceback: suffix = ' at:\n%s' % ''.join( chop_traceback(self._checkout_traceback)) else: suffix = '' raise AssertionError("connection is already checked out" + suffix) if not self._conn: self._conn = self._create_connection() self._checked_out = True if self._store_traceback: self._checkout_traceback = traceback.format_stack() return self._conn class _DBProxy(object): """Layers connection pooling behavior on top of a standard DB-API module. Proxies a DB-API 2.0 connect() call to a connection pool keyed to the specific connect parameters. Other functions and attributes are delegated to the underlying DB-API module. """ def __init__(self, module, poolclass=QueuePool, **kw): """Initializes a new proxy. module a DB-API 2.0 module poolclass a Pool class, defaulting to QueuePool Other parameters are sent to the Pool object's constructor. """ self.module = module self.kw = kw self.poolclass = poolclass self.pools = {} self._create_pool_mutex = threading.Lock() def close(self): for key in self.pools.keys(): del self.pools[key] def __del__(self): self.close() def __getattr__(self, key): return getattr(self.module, key) def get_pool(self, *args, **kw): key = self._serialize(*args, **kw) try: return self.pools[key] except KeyError: self._create_pool_mutex.acquire() try: if key not in self.pools: kw.pop('sa_pool_key', None) pool = self.poolclass(lambda: self.module.connect(*args, **kw), **self.kw) self.pools[key] = pool return pool else: return self.pools[key] finally: self._create_pool_mutex.release() def connect(self, *args, **kw): """Activate a connection to the database. Connect to the database using this DBProxy's module and the given connect arguments. If the arguments match an existing pool, the connection will be returned from the pool's current thread-local connection instance, or if there is no thread-local connection instance it will be checked out from the set of pooled connections. If the pool has no available connections and allows new connections to be created, a new database connection will be made. """ return self.get_pool(*args, **kw).connect() def dispose(self, *args, **kw): """Dispose the pool referenced by the given connect arguments.""" key = self._serialize(*args, **kw) try: del self.pools[key] except KeyError: pass def _serialize(self, *args, **kw): if "sa_pool_key" in kw: return kw['sa_pool_key'] return tuple( list(args) + [(k, kw[k]) for k in sorted(kw)] )