# pool.py - Connection pooling for SQLAlchemy
# Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Michael Bayer mike_mp@zzzcomputing.com
#
# 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 weakref, time, threading
from sqlalchemy import exc,log
from sqlalchemy import queue
from sqlalchemy.util import threading,pickle,as_interface,memoized_property
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()
class Pool(log.Identified):
"""Abstract base class for connection pools."""
def __init__(self,
creator, recycle=-1, echo=None,
use_threadlocal=False,
logging_name=None,
reset_on_return=True, listeners=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: If true, reset the database state of
connections returned to the pool. This is typically a
ROLLBACK to release locks and transaction resources.
Disable at your own peril. Defaults to True.
: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.
"""
if logging_name:
self.logging_name = logging_name
self.logger = log.instance_logger(self, echoflag=echo)
self._threadconns = threading.local()
self._creator = creator
self._recycle = recycle
self._use_threadlocal = use_threadlocal
self._reset_on_return = reset_on_return
self.echo = echo
self.listeners = []
self._on_connect = []
self._on_first_connect = []
self._on_checkout = []
self._on_checkin = []
if listeners:
for l in listeners:
self.add_listener(l)
def unique_connection(self):
return _ConnectionFairy(self).checkout()
def create_connection(self):
return _ConnectionRecord(self)
def recreate(self):
"""Return a new instance with identical creation arguments."""
raise NotImplementedError()
def dispose(self):
"""Dispose of this pool.
This method leaves the possibility of checked-out connections
remaining open, It is advised to not reuse the pool once dispose()
is called, and to instead use a new pool constructed by the
recreate() method.
"""
raise NotImplementedError()
def connect(self):
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):
if self._use_threadlocal and hasattr(self._threadconns, "current"):
del self._threadconns.current
self.do_return_conn(record)
def get(self):
return self.do_get()
def do_get(self):
raise NotImplementedError()
def do_return_conn(self, conn):
raise NotImplementedError()
def status(self):
raise NotImplementedError()
def add_listener(self, listener):
"""Add a ``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.
"""
listener = as_interface(listener,
methods=('connect', 'first_connect', 'checkout', 'checkin'))
self.listeners.append(listener)
if hasattr(listener, 'connect'):
self._on_connect.append(listener)
if hasattr(listener, 'first_connect'):
self._on_first_connect.append(listener)
if hasattr(listener, 'checkout'):
self._on_checkout.append(listener)
if hasattr(listener, 'checkin'):
self._on_checkin.append(listener)
class _ConnectionRecord(object):
def __init__(self, pool):
self.__pool = pool
self.connection = self.__connect()
self.info = {}
ls = pool.__dict__.pop('_on_first_connect', None)
if ls is not None:
for l in ls:
l.first_connect(self.connection, self)
if pool._on_connect:
for l in pool._on_connect:
l.connect(self.connection, self)
def close(self):
if self.connection is not None:
self.__pool.logger.debug("Closing connection %r", self.connection)
try:
self.connection.close()
except (SystemExit, KeyboardInterrupt):
raise
except:
self.__pool.logger.debug("Exception closing connection %r",
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._on_connect:
for l in self.__pool._on_connect:
l.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._on_connect:
for l in self.__pool._on_connect:
l.connect(self.connection, self)
return self.connection
def __close(self):
try:
self.__pool.logger.debug("Closing connection %r", self.connection)
self.connection.close()
except (SystemExit, KeyboardInterrupt):
raise
except Exception, e:
self.__pool.logger.debug("Connection %r threw an error on close: %s",
self.connection, e)
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=None):
_refs.discard(connection_record)
if ref is not None and (connection_record.fairy is not ref or isinstance(pool, AssertionPool)):
return
if connection is not None:
try:
if pool._reset_on_return:
connection.rollback()
# Immediately close detached instances
if connection_record is None:
connection.close()
except Exception, e:
if connection_record is not None:
connection_record.invalidate(e=e)
if isinstance(e, (SystemExit, KeyboardInterrupt)):
raise
if connection_record is not None:
connection_record.fairy = None
pool.logger.debug("Connection %r being returned to pool", connection)
if pool._on_checkin:
for l in pool._on_checkin:
l.checkin(connection, connection_record)
pool.return_conn(connection_record)
_refs = set()
class _ConnectionFairy(object):
"""Proxies a DB-API connection and provides return-on-dereference support."""
__slots__ = '_pool', '__counter', 'connection', \
'_connection_record', '__weakref__', '_detached_info'
def __init__(self, pool):
self._pool = pool
self.__counter = 0
try:
rec = self._connection_record = pool.get()
conn = self.connection = self._connection_record.get_connection()
rec.fairy = weakref.ref(self, lambda ref:_finalize_fairy(conn, rec, pool, ref))
_refs.add(rec)
except:
self.connection = None # helps with endless __getattr__ loops later on
self._connection_record = None
raise
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
@property
def info(self):
"""An info collection unique to this DB-API connection."""
try:
return self._connection_record.info
except AttributeError:
if self.connection is None:
raise exc.InvalidRequestError("This connection is closed")
try:
return self._detached_info
except AttributeError:
self._detached_info = value = {}
return value
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):
try:
c = self.connection.cursor(*args, **kwargs)
return _CursorFairy(self, c)
except Exception, e:
self.invalidate(e=e)
raise
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._on_checkout or self.__counter != 1:
return self
# Pool listeners can trigger a reconnection on checkout
attempts = 2
while attempts > 0:
try:
for l in self._pool._on_checkout:
l.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._detached_info = \
self._connection_record.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)
self.connection = None
self._connection_record = None
class _CursorFairy(object):
__slots__ = '_parent', 'cursor', 'execute'
def __init__(self, parent, cursor):
self._parent = parent
self.cursor = cursor
self.execute = cursor.execute
def invalidate(self, e=None):
self._parent.invalidate(e=e)
def __iter__(self):
return iter(self.cursor)
def close(self):
try:
self.cursor.close()
except Exception, e:
try:
ex_text = str(e)
except TypeError:
ex_text = repr(e)
self.__parent._logger.warn("Error closing cursor: %s", ex_text)
if isinstance(e, (SystemExit, KeyboardInterrupt)):
raise
def __setattr__(self, key, value):
if key in self.__slots__:
object.__setattr__(self, key, value)
else:
setattr(self.cursor, key, value)
def __getattr__(self, key):
return getattr(self.cursor, key)
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.
This is used for SQLite, which both does not handle multithreading by
default, and also requires a singleton connection if a :memory: database
is being used.
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.
"""
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 SingletonThreadPool(self._creator,
pool_size=self.size,
recycle=self._recycle,
echo=self.echo,
use_threadlocal=self._use_threadlocal,
listeners=self.listeners)
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 dispose_local(self):
if hasattr(self._conn, 'current'):
conn = self._conn.current()
self._all_conns.discard(conn)
del self._conn.current
def cleanup(self):
while len(self._all_conns) > self.size:
self._all_conns.pop()
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 QueuePool(Pool):
"""A Pool that imposes a limit on the number of open connections."""
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. 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. Defaults to 5.
: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: If true, reset the database state of
connections returned to the pool. This is typically a
ROLLBACK to release locks and transaction resources.
Disable at your own peril. Defaults to True.
: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 = self._max_overflow > -1 and threading.Lock() or None
def recreate(self):
self.logger.info("Pool recreating")
return QueuePool(self._creator, pool_size=self._pool.maxsize,
max_overflow=self._max_overflow, timeout=self._timeout,
recycle=self._recycle, echo=self.echo,
use_threadlocal=self._use_threadlocal, listeners=self.listeners)
def do_return_conn(self, conn):
try:
self._pool.put(conn, False)
except sqla_queue.Full:
if self._overflow_lock is None:
self._overflow -= 1
else:
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.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))
if self._overflow_lock is not None:
self._overflow_lock.acquire()
if self._max_overflow > -1 and self._overflow >= self._max_overflow:
if self._overflow_lock is not None:
self._overflow_lock.release()
return self.do_get()
try:
con = self.create_connection()
self._overflow += 1
finally:
if self._overflow_lock is not None:
self._overflow_lock.release()
return con
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 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.
"""
def status(self):
return "NullPool"
def do_return_conn(self, conn):
conn.close()
def do_return_invalid(self, conn):
pass
def do_get(self):
return self.create_connection()
def recreate(self):
self.logger.info("Pool recreating")
return NullPool(self._creator,
recycle=self._recycle,
echo=self.echo,
use_threadlocal=self._use_threadlocal,
listeners=self.listeners)
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,
listeners=self.listeners)
def create_connection(self):
return self._conn
def do_return_conn(self, conn):
pass
def do_return_invalid(self, conn):
pass
def do_get(self):
return self.connection
class AssertionPool(Pool):
"""A 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.
"""
def __init__(self, *args, **kw):
self._conn = None
self._checked_out = False
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 do_return_invalid(self, conn):
self._conn = None
self._checked_out = False
def dispose(self):
self._checked_out = False
if self._conn:
self._conn.close()
def recreate(self):
self.logger.info("Pool recreating")
return AssertionPool(self._creator, echo=self.echo,
listeners=self.listeners)
def do_get(self):
if self._checked_out:
raise AssertionError("connection is already checked out")
if not self._conn:
self._conn = self.create_connection()
self._checked_out = True
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:
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):
return pickle.dumps([args, kw])
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