psycopg2.pool – Connections pooling

Creating new PostgreSQL connections can be an expensive operation. This module offers a few pure Python classes implementing simple connection pooling directly in the client application.

class psycopg2.pool.AbstractConnectionPool(minconn, maxconn, *args, **kwargs)

Base class implementing generic key-based pooling code.

New minconn connections are created automatically. The pool will support a maximum of about maxconn connections. *args and **kwargs are passed to the connect() function.

The following methods are expected to be implemented by subclasses:


Get a free connection from the pool.

The key parameter is optional: if used, the connection will be associated to the key and calling getconn() with the same key again will return the same connection.

putconn(conn, key=None, close=False)

Put away a connection.

If close is True, discard the connection from the pool. key should be used consistently with getconn().


Close all the connections handled by the pool.

Note that all the connections are closed, including ones eventually in use by the application.

The following classes are AbstractConnectionPool subclasses ready to be used.

class psycopg2.pool.SimpleConnectionPool(minconn, maxconn, *args, **kwargs)

A connection pool that can’t be shared across different threads.


This pool class is useful only for single-threaded applications.

class psycopg2.pool.ThreadedConnectionPool(minconn, maxconn, *args, **kwargs)

A connection pool that works with the threading module.


This pool class can be safely used in multi-threaded applications.

class psycopg2.pool.PersistentConnectionPool(minconn, maxconn, *args, **kwargs)

A pool that assigns persistent connections to different threads.

Note that this connection pool generates by itself the required keys using the current thread id. This means that until a thread puts away a connection it will always get the same connection object by successive getconn() calls. This also means that a thread can’t use more than one single connection from the pool.


This pool class is mostly designed to interact with Zope and probably not useful in generic applications.