SessionPool Object

Note

This object is an extension to the DB API.

Connection pooling in cx_Oracle is handled by SessionPool objects.

See Connection Pooling for information on connection pooling.

SessionPool.acquire(user=None, password=None, cclass=None, purity=cx_Oracle.ATTR_PURITY_DEFAULT, tag=None, matchanytag=False, shardingkey=[], supershardingkey=[])

Acquire a connection from the session pool and return a connection object.

If the pool is homogeneous, the user and password parameters cannot be specified. If they are, an exception will be raised.

The cclass parameter, if specified, should be a string corresponding to the connection class for database resident connection pooling (DRCP).

The purity parameter is expected to be one of ATTR_PURITY_NEW, ATTR_PURITY_SELF, or ATTR_PURITY_DEFAULT.

The tag parameter, if specified, is expected to be a string with name=value pairs like “k1=v1;k2=v2” and will limit the sessions that can be returned from a session pool unless the matchanytag parameter is set to True. In that case sessions with the specified tag will be preferred over others, but if no such sessions are available a session with a different tag may be returned instead. In any case, untagged sessions will always be returned if no sessions with the specified tag are available. Sessions are tagged when they are released back to the pool.

The shardingkey and supershardingkey parameters, if specified, are expected to be a sequence of values which will be used to identify the database shard to connect to. The key values can be strings, numbers, bytes or dates.

SessionPool.busy

This read-only attribute returns the number of sessions currently acquired.

SessionPool.close(force=False)

Close the session pool now, rather than when the last reference to it is released, which makes it unusable for further work.

If any connections have been acquired and not released back to the pool this method will fail unless the force parameter is set to True.

SessionPool.drop(connection)

Drop the connection from the pool which is useful if the connection is no longer usable (such as when the session is killed).

SessionPool.dsn

This read-only attribute returns the TNS entry of the database to which a connection has been established.

SessionPool.getmode

This read-write attribute determines how connections are returned from the pool. If SPOOL_ATTRVAL_FORCEGET is specified, a new connection will be returned even if there are no free sessions in the pool. SPOOL_ATTRVAL_NOWAIT will raise an exception if there are no free sessions are available in the pool. If SPOOL_ATTRVAL_WAIT is specified and there are no free sessions in the pool, the caller will wait until a free session is available. SPOOL_ATTRVAL_TIMEDWAIT uses the value of wait_timeout to determine how long the caller should wait for a session to become available before returning an error.

SessionPool.homogeneous

This read-write boolean attribute indicates whether the pool is considered homogeneous or not. If the pool is not homogeneous different authentication can be used for each connection acquired from the pool.

SessionPool.increment

This read-only attribute returns the number of sessions that will be established when additional sessions need to be created.

SessionPool.max

This read-only attribute returns the maximum number of sessions that the session pool can control.

SessionPool.max_lifetime_session

This read-write attribute returns the maximum length of time (in seconds) that a pooled session may exist. Sessions that are in use will not be closed. They become candidates for termination only when they are released back to the pool and have existed for longer than max_lifetime_session seconds. Note that termination only occurs when the pool is accessed. A value of 0 means that there is no maximum length of time that a pooled session may exist. This attribute is only available in Oracle Database 12.1.

New in version 5.3.

SessionPool.max_sessions_per_shard

This read-write attribute returns the number of sessions that can be created per shard in the pool. Setting this attribute greater than zero specifies the maximum number of sessions in the pool that can be used for any given shard in a sharded database. This lets connections in the pool be balanced across the shards. A value of zero will not set any maximum number of sessions for each shard. This attribute is only available in Oracle Client 18.3 and higher.

New in version 8.2.

SessionPool.min

This read-only attribute returns the number of sessions with which the session pool was created and the minimum number of sessions that will be controlled by the session pool.

SessionPool.name

This read-only attribute returns the name assigned to the session pool by Oracle.

SessionPool.opened

This read-only attribute returns the number of sessions currently opened by the session pool.

SessionPool.ping_interval

This read-write integer attribute specifies the pool ping interval in seconds. When a connection is acquired from the pool, a check is first made to see how long it has been since the connection was put into the pool. If this idle time exceeds ping_interval, then a round-trip ping to the database is performed. If the connection is unusable, it is discarded and a different connection is selected to be returned by SessionPool.acquire(). Setting ping_interval to a negative value disables pinging. Setting it to 0 forces a ping for every acquire() and is not recommended.

Prior to cx_Oracle 8.2, the ping interval was fixed at 60 seconds.

New in version 8.2.

SessionPool.reconfigure([min, max, increment, getmode, timeout, wait_timeout, max_lifetime_session, max_sessions_per_shard, soda_metadata_cache, stmtcachesize, ping_interval])

Reconfigures various parameters of a connection pool. The pool size can be altered with reconfigure() by passing values for min, max or increment. The getmode, timeout, wait_timeout, max_lifetime_session, max_sessions_per_shard, soda_metadata_cache, stmtcachesize and ping_interval attributes can be set directly or with reconfigure().

All parameters are optional. Unspecified parameters will leave those pool attributes unchanged. The parameters are processed in two stages. After any size change has been processed, reconfiguration on the other parameters is done sequentially. If an error such as an invalid value occurs when changing one attribute, then an exception will be generated but any already changed attributes will retain their new values.

During reconfiguration of a pool’s size, the behavior of SessionPool.acquire() depends on the getmode in effect when acquire() is called:

  • With mode SPOOL_ATTRVAL_FORCEGET, an acquire() call will wait until the pool has been reconfigured.

  • With mode SPOOL_ATTRVAL_TIMEDWAIT, an acquire() call will try to acquire a connection in the time specified by wait_timeout and return an error if the time taken exceeds that value.

  • With mode SPOOL_ATTRVAL_WAIT, an acquire() call will wait until after the pool has been reconfigured and a connection is available.

  • With mode SPOOL_ATTRVAL_NOWAIT, if the number of busy connections is less than the pool size, acquire() will return a new connection after pool reconfiguration is complete.

Closing connections with SessionPool.release() or Connection.close() will wait until any pool size reconfiguration is complete.

Closing the connection pool with SessionPool.close() will wait until reconfiguration is complete.

See Connection Pool Reconfiguration.

New in version 8.2.

SessionPool.release(connection, tag=None)

Release the connection back to the pool now, rather than whenever __del__ is called. The connection will be unusable from this point forward; an Error exception will be raised if any operation is attempted with the connection. Any cursors or LOBs created by the connection will also be marked unusable and an Error exception will be raised if any operation is attempted with them.

Internally, references to the connection are held by cursor objects, LOB objects, etc. Once all of these references are released, the connection itself will be released back to the pool automatically. Either control references to these related objects carefully or explicitly release connections back to the pool in order to ensure sufficient resources are available.

If the tag is not None, it is expected to be a string with name=value pairs like “k1=v1;k2=v2” and will override the value in the property Connection.tag. If either Connection.tag or the tag parameter are not None, the connection will be retagged when it is released back to the pool.

SessionPool.soda_metadata_cache

This read-write boolean attribute returns whether the SODA metadata cache is enabled or not. Enabling the cache significantly improves the performance of methods SodaDatabase.createCollection() (when not specifying a value for the metadata parameter) and SodaDatabase.openCollection(). Note that the cache can become out of date if changes to the metadata of cached collections are made externally.

New in version 8.2.

SessionPool.stmtcachesize

This read-write attribute specifies the size of the statement cache that will be used for connections obtained from the pool.

See Statement Caching for more information.

New in version 6.0.

SessionPool.timeout

This read-write attribute specifies the time (in seconds) after which idle sessions will be terminated in order to maintain an optimum number of open sessions. Note that termination only occurs when the pool is accessed. A value of 0 means that no idle sessions are terminated.

SessionPool.tnsentry

This read-only attribute returns the TNS entry of the database to which a connection has been established.

Deprecated since version 8.2: Use the attribute dsn instead.

SessionPool.username

This read-only attribute returns the name of the user which established the connection to the database.

SessionPool.wait_timeout

This read-write attribute specifies the time (in milliseconds) that the caller should wait for a session to become available in the pool before returning with an error. This value is only used if the getmode parameter to cx_Oracle.SessionPool() was the value cx_Oracle.SPOOL_ATTRVAL_TIMEDWAIT.

New in version 6.4.