# pool.py - Connection pooling for SQLAlchemy # Copyright (C) 2005, 2006, 2007 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 """provides a connection pool implementation, which optionally manages connections on a thread local basis. Also provides a DBAPI2 transparency layer so that pools can be managed automatically, based on module type and connect arguments, simply by calling regular DBAPI connect() methods.""" import weakref, string, time, sys, traceback try: import cPickle as pickle except: import pickle from sqlalchemy import exceptions, logging from sqlalchemy import queue as Queue try: import thread except: import dummy_thread as thread proxies = {} def manage(module, **params): """given a DBAPI2 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. Arguments: module : a DBAPI2 database module. poolclass=QueuePool : the class used by the pool module to provide pooling. Options: See Pool for options. """ try: return proxies[module] except KeyError: return proxies.setdefault(module, _DBProxy(module, **params)) def clear_managers(): """removes all current DBAPI2 managers. all pools and connections are disposed.""" for manager in proxies.values(): manager.close() proxies.clear() class Pool(object): """Base Pool class. This is an abstract class, which is implemented by various subclasses including: QueuePool - pools multiple connections using Queue.Queue SingletonThreadPool - stores a single connection per execution thread NullPool - doesnt do any pooling; opens and closes connections AssertionPool - stores only one connection, and asserts that only one connection is checked out at a time. the main argument, "creator", is a callable function that returns a newly connected DBAPI connection object. Options that are understood by Pool are: echo=False : if set to True, connections being pulled and retrieved from/to 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. use_threadlocal=True : if set to True, repeated calls to 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. This allows code to retrieve a connection from the pool, and then while still holding on to that connection, to call other functions which also ask the pool for a connection of the same arguments; those functions will act upon the same connection that the calling method is using. recycle=-1 : if set to non -1, a 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. auto_close_cursors = True : cursors, returned by connection.cursor(), are tracked and are automatically closed when the connection is returned to the pool. some DBAPIs like MySQLDB become unstable if cursors remain open. disallow_open_cursors = False : if auto_close_cursors is False, and disallow_open_cursors is True, will raise an exception if an open cursor is detected upon connection checkin. If auto_close_cursors and disallow_open_cursors are both False, then no cursor processing occurs upon checkin. """ def __init__(self, creator, recycle=-1, echo=None, use_threadlocal=False, auto_close_cursors=True, disallow_open_cursors=False): self.logger = logging.instance_logger(self) self._threadconns = weakref.WeakValueDictionary() self._creator = creator self._recycle = recycle self._use_threadlocal = use_threadlocal self.auto_close_cursors = auto_close_cursors self.disallow_open_cursors = disallow_open_cursors self.echo = echo echo = logging.echo_property() def unique_connection(self): return _ConnectionFairy(self).checkout() def create_connection(self): return _ConnectionRecord(self) def connect(self): if not self._use_threadlocal: return _ConnectionFairy(self).checkout() try: return self._threadconns[thread.get_ident()].connfairy().checkout() except KeyError: agent = _ConnectionFairy(self).checkout() self._threadconns[thread.get_ident()] = agent._threadfairy return agent def return_conn(self, agent): self.do_return_conn(agent._connection_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 log(self, msg): self.logger.info(msg) def dispose(self): raise NotImplementedError() class _ConnectionRecord(object): def __init__(self, pool): self.__pool = pool self.connection = self.__connect() def close(self): self.__pool.log("Closing connection %s" % repr(self.connection)) self.connection.close() def invalidate(self): self.__pool.log("Invalidate connection %s" % repr(self.connection)) self.__close() self.connection = None def get_connection(self): if self.connection is None: self.connection = self.__connect() elif (self.__pool._recycle > -1 and time.time() - self.starttime > self.__pool._recycle): self.__pool.log("Connection %s exceeded timeout; recycling" % repr(self.connection)) self.__close() self.connection = self.__connect() return self.connection def __close(self): try: self.__pool.log("Closing connection %s" % (repr(self.connection))) self.connection.close() except Exception, e: self.__pool.log("Connection %s threw an error on close: %s" % (repr(self.connection), str(e))) def __connect(self): try: self.starttime = time.time() connection = self.__pool._creator() self.__pool.log("Created new connection %s" % repr(connection)) return connection except Exception, e: self.__pool.log("Error on connect(): %s" % (str(e))) raise class _ThreadFairy(object): """marks a thread identifier as owning a connection, for a thread local pool.""" def __init__(self, connfairy): self.connfairy = weakref.ref(connfairy) class _ConnectionFairy(object): """proxies a DBAPI connection object and provides return-on-dereference support""" def __init__(self, pool): self._threadfairy = _ThreadFairy(self) self._cursors = weakref.WeakKeyDictionary() self.__pool = pool self.__counter = 0 try: self._connection_record = pool.get() self.connection = self._connection_record.get_connection() except: self.connection = None # helps with endless __getattr__ loops later on self._connection_record = None raise if self.__pool.echo: self.__pool.log("Connection %s checked out from pool" % repr(self.connection)) def invalidate(self): if self.connection is None: raise exceptions.InvalidRequestError("This connection is closed") self._connection_record.invalidate() self.connection = None self._cursors = None self._close() def cursor(self, *args, **kwargs): try: return _CursorFairy(self, self.connection.cursor(*args, **kwargs)) except Exception, e: self.invalidate() raise def __getattr__(self, key): return getattr(self.connection, key) def checkout(self): if self.connection is None: raise exceptions.InvalidRequestError("This connection is closed") self.__counter +=1 return self def close_open_cursors(self): if self._cursors is not None: for c in list(self._cursors): c.close() def close(self): self.__counter -=1 if self.__counter == 0: self._close() def __del__(self): self._close() def _close(self): if self._cursors is not None: # cursors should be closed before connection is returned to the pool. some dbapis like # mysql have real issues if they are not. if self.__pool.auto_close_cursors: self.close_open_cursors() elif self.__pool.disallow_open_cursors: if len(self._cursors): raise exceptions.InvalidRequestError("This connection still has %d open cursors" % len(self._cursors)) if self.connection is not None: try: self.connection.rollback() except: if self._connection_record is not None: self._connection_record.invalidate() if self._connection_record is not None: if self.__pool.echo: self.__pool.log("Connection %s being returned to pool" % repr(self.connection)) self.__pool.return_conn(self) self.connection = None self._connection_record = None self._threadfairy = None self._cursors = None class _CursorFairy(object): def __init__(self, parent, cursor): self.__parent = parent self.__parent._cursors[self]=True self.cursor = cursor def invalidate(self): self.__parent.invalidate() def close(self): if self in self.__parent._cursors: del self.__parent._cursors[self] self.cursor.close() def __getattr__(self, key): return getattr(self.cursor, key) class SingletonThreadPool(Pool): """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 Pool, as well as: pool_size=5 - the number of threads in which to maintain connections at once.""" def __init__(self, creator, pool_size=5, **params): params['use_threadlocal'] = True Pool.__init__(self, creator, **params) self._conns = {} self.size = pool_size def dispose(self): for key, conn in self._conns.items(): try: conn.close() except: # sqlite won't even let you close a conn from a thread that didn't create it pass del self._conns[key] def dispose_local(self): try: del self._conns[thread.get_ident()] except KeyError: pass def cleanup(self): for key in self._conns.keys(): try: del self._conns[key] except KeyError: pass if len(self._conns) <= self.size: return def status(self): return "SingletonThreadPool id:%d thread:%d size: %d" % (id(self), thread.get_ident(), len(self._conns)) def do_return_conn(self, conn): pass def do_get(self): try: return self._conns[thread.get_ident()] except KeyError: c = self.create_connection() self._conns[thread.get_ident()] = c if len(self._conns) > self.size: self.cleanup() return c class QueuePool(Pool): """uses Queue.Queue to maintain a fixed-size list of connections. Arguments include all those used by the base Pool class, as well as: pool_size=5 : 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. max_overflow=10 : 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. timeout=30 : the number of seconds to wait before giving up on returning a connection """ def __init__(self, creator, pool_size = 5, max_overflow = 10, timeout=30, **params): Pool.__init__(self, creator, **params) self._pool = Queue.Queue(pool_size) self._overflow = 0 - pool_size self._max_overflow = max_overflow self._timeout = timeout def do_return_conn(self, conn): try: self._pool.put(conn, False) except Queue.Full: self._overflow -= 1 def do_get(self): try: return self._pool.get(self._max_overflow > -1 and self._overflow >= self._max_overflow, self._timeout) except Queue.Empty: if self._max_overflow > -1 and self._overflow >= self._max_overflow: raise exceptions.TimeoutError("QueuePool limit of size %d overflow %d reached, connection timed out" % (self.size(), self.overflow())) con = self.create_connection() self._overflow += 1 return con def dispose(self): while True: try: conn = self._pool.get(False) conn.close() except Queue.Empty: break self._overflow = 0 - self.size() self.log("Pool disposed. " + self.status()) def status(self): tup = (self.size(), self.checkedin(), self.overflow(), self.checkedout()) return "Pool size: %d Connections in pool: %d Current Overflow: %d Current Checked out connections: %d" % tup 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 implementation which does not pool connections; instead it literally opens and closes the underlying DBAPI connection per each connection open/close.""" 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() class AssertionPool(Pool): """a Pool implementation which 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. TODO: modify this to handle an arbitrary connection count.""" def __init__(self, creator, **params): Pool.__init__(self, creator, **params) self.connection = _ConnectionRecord(self) self._conn = self.connection def status(self): return "AssertionPool" def create_connection(self): raise "Invalid" def do_return_conn(self, conn): assert conn is self._conn and self.connection is None self.connection = conn def do_return_invalid(self, conn): raise "Invalid" def do_get(self): assert self.connection is not None c = self.connection self.connection = None return c class _DBProxy(object): """proxies a DBAPI2 connect() call to a pooled connection keyed to the specific connect parameters. other attributes are proxied through via __getattr__.""" def __init__(self, module, poolclass = QueuePool, **params): """ module is a DBAPI2 module poolclass is a Pool class, defaulting to QueuePool. other parameters are sent to the Pool object's constructor. """ self.module = module self.params = params self.poolclass = poolclass self.pools = {} 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, **params): key = self._serialize(*args, **params) try: return self.pools[key] except KeyError: pool = self.poolclass(lambda: self.module.connect(*args, **params), **self.params) self.pools[key] = pool return pool def connect(self, *args, **params): """connects to a 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, **params).connect() def dispose(self, *args, **params): """disposes the connection pool referenced by the given connect arguments.""" key = self._serialize(*args, **params) try: del self.pools[key] except KeyError: pass def _serialize(self, *args, **params): return pickle.dumps([args, params])