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 ~Connection.prepare_threshold times on a connection. !psycopg will make sure that no more than ~Connection.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 ~Connection.prepare_threshold attribute to !None.

.. versionchanged:: 3.1 You can set !prepare_threshold as a ~Connection.connect() keyword parameter too.

.. seealso::

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

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

.. __: https://www.postgresql.org/docs/current/sql-prepare.html

.. _pgbouncer:

Using prepared statements with PgBouncer

.. warning::

Unless a connection pooling middleware explicitly declares otherwise, they
are 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`.

Starting from 3.2, Psycopg supports prepared statements when using the PgBouncer__ middleware, using the following caveats:

PgBouncer version must be version 1.22__ or newer.
PgBouncer max_prepared_statements__ must be greater than 0.
The libpq version on the client must be from PostgreSQL 17 or newer (you can check the ~Capabilities.has_send_close_prepared() capability to verify that the libpq implements the features required by PgBouncer).

.. __: https://www.pgbouncer.org/ .. __: https://www.pgbouncer.org/2024/01/pgbouncer-1-22-0 .. __: https://www.pgbouncer.org/config.html#max_prepared_statements

.. hint::

If libpq 17 is not available on your client, but PgBouncer is 1.22 or
higher, you can still use Psycopg *as long as you disable deallocation*.

You can do so by setting `Connection.prepared_max` to `!None`.