Connection Pooling {@name=pooling}
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-SQLAlchemy uses *connection pooling* to increase efficiency and control resource consumption. Pooling is setup automaticaly during `Engine` creation and you don't need to do anything special to take advantage of it.
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-A connection pool aims to extend the lifetime of a database connection as long as possible. Instead of closing the connection to the database when work is complete, a pooled connection returns to its "pool" and remains open. It can then be re-used for the next caller that needs a database connection. Callers requesting a connection from the pool may receive a brand new database connection or a recycled connection.
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-In SQLAlchemy, interaction with the pool is largely transaparent. When you request a database connection with ``connect()``, for example, a connection will be retrieved from the pool. Calling ``close()`` on that connection will return it to the pool.
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This section describes the connection pool module of SQLAlchemy. The `Pool` object it provides is normally embedded within an `Engine` instance. For most cases, explicit access to the pool module is not required. However, the `Pool` object can be used on its own, without the rest of SA, to manage DBAPI connections; this section describes that usage. Also, this section will describe in more detail how to customize the pooling strategy used by an `Engine`.
At the base of any database helper library is a system of efficiently acquiring connections to the database. Since the establishment of a database connection is typically a somewhat expensive operation, an application needs a way to get at database connections repeatedly without incurring the full overhead each time. Particularly for server-side web applications, a connection pool is the standard way to maintain a "pool" of database connections which are used over and over again among many requests. Connection pools typically are configured to maintain a certain "size", which represents how many connections can be used simultaneously without resorting to creating more newly-established connections.