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  7. Prepared statements
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Prepared statements

Psycopg uses an automatic system to manage prepared statements. When a query is prepared, its parsing and planning is stored in the server session, so that further executions of the same query on the same connection (even with different parameters) are optimised.

A query is prepared automatically after it is executed more than prepare_threshold times on a connection. psycopg will make sure that no more than prepared_max statements are planned: if further queries are executed, the least recently used ones are deallocated and the associated resources freed.

Statement preparation can be controlled in several ways:

  • You can decide to prepare a query immediately by passing prepare=True to Connection.execute() or Cursor.execute(). The query is prepared, if it wasn’t already, and executed as prepared from its first use.
  • Conversely, passing prepare=False to execute() will avoid to prepare the query, regardless of the number of times it is executed. The default for the parameter is None, meaning that the query is prepared if the conditions described above are met.
  • You can disable the use of prepared statements on a connection by setting its prepare_threshold attribute to None.

Changed in version 3.1: You can set prepare_threshold as a connect() keyword parameter too.

The PREPARE PostgreSQL documentation contains plenty of details about prepared statements in PostgreSQL.

Note however that Psycopg doesn’t use SQL statements such as PREPARE and EXECUTE, but protocol level commands such as the ones exposed by PQsendPrepare, PQsendQueryPrepared.

Using external connection poolers, such as PgBouncer, is not compatible with prepared statements, because the same client connection may change the server session it refers to. If such middleware is used you should disable prepared statements, by setting the Connection.prepare_threshold attribute to None.