Session pool settings

Configure session pool settings.

This administrative console page is common to JMS unified connection factories, queue connection factories and topic connection factories. To view this page, we select an instance of the resource type then click Session pools. For example, click...

        Resources > JMS->Queue connection factories->queue_connection_factory->[Additional Properties] Session pools.

Connection Timeout

The interval, in seconds, after which a connection request times out and a ConnectionWaitTimeoutException is thrown.

The wait is necessary when the maximum value of connections (Max Connections) to a particular connection pool is reached . For example, if Connection Timeout is set to 300 and the maximum number of connections is reached, the Pool Manager waits for 300 seconds for an available physical connection. If a physical connection is not available within this time, the Pool Manager throws a ConnectionWaitTimeoutException. It usually does not make sense to retry the getConnection() method, because if a longer wait time is required, we should set the Connection Timeout setting to a higher value. Therefore, if this exception is caught by the application, the administrator should review the expected usage of the application and tune the connection pool and the database accordingly.

If Connection Timeout is set to 0, the Pool Manager waits as long as necessary until a connection is allocated (which happens when the number of connections falls below the value of Max Connections).

If Max Connections is set to 0, which enables an infinite number of physical connections, then the Connection Timeout value is ignored.

Information	Value
Data type	Integer
Units	Seconds
Default	180
Range	0 to max int

Max Connections

Maximum number of physical connections that we can create in this pool.

These are the physical connections to the backend resource. Once this number is reached, no new physical connections are created and the requester waits until a physical connection that is currently in use returns to the pool, or a ConnectionWaitTimeoutException is thrown.

For example, if the Max Connections value is set to 5, and there are five physical connections in use, the pool manager waits for the amount of time specified in Connection Timeout for a physical connection to become free.

If Max Connections is set to 0, the Connection Timeout value is ignored.

For better performance, set the value for the connection pool lower than the value for the Max Connections option in the web container. Lower settings, such as 10-30 connections, perform better than higher settings, such as 100.

If clones are used, one data pool exists for each clone. Knowing the number of data pools is important when configuring the database maximum connections.

Use the Tivoli Performance Viewer to find the optimal number of connections in a pool. If the number of concurrent waiters is greater than 0, but the CPU load is not close to 100%, consider increasing the connection pool size. If the Percent Used value is consistently low under normal workload, consider decreasing the number of connections in the pool.

Information	Value
Data type	Integer
Default	10
Range	0 to max int

Min Connections

Minimum number of physical connections to maintain.

Until this number is reached, the pool maintenance thread does not discard physical connections. However, no attempt is made to bring the number of connections up to this number. If we set a value for Aged Timeout, the minimum is not maintained. All connections with an expired age are discarded.

For example if the Min Connections value is set to 3, and one physical connection is created, the Unused Timeout thread does not discard that connection. By the same token, the thread does not automatically create two additional physical connections to reach the Min Connections setting.

Information	Value
Data type	Integer
Default	1
Range	0 to max int

Reap Time

The interval, in seconds, between runs of the pool maintenance thread.

For example, if Reap Time is set to 60, the pool maintenance thread runs every 60 seconds. The Reap Time interval affects the accuracy of the Unused Timeout and Aged Timeout settings. The smaller the interval, the greater the accuracy. If the pool maintenance thread is enabled, set the Reap Time value less than the values of Unused Timeout and Aged Timeout. When the pool maintenance thread runs, it discards any connections remaining unused for longer than the time value specified in Unused Timeout, until it reaches the number of connections specified in Min Connections. The pool maintenance thread also discards any connections that remain active longer than the time value specified in Aged Timeout.

The Reap Time interval also affects performance. Smaller intervals mean that the pool maintenance thread runs more often and degrades performance.

To disable the pool maintenance thread set Reap Time to 0, or set both Unused Timeout and Aged Timeout to 0. The recommended way to disable the pool maintenance thread is to set Reap Time to 0, in which case Unused Timeout and Aged Timeout are ignored. However, if Unused Timeout and Aged Timeout are set to 0, the pool maintenance thread runs, but only physical connections that timeout due to non-zero timeout values are discarded.

Information	Value
Data type	Integer
Units	Seconds
Default	180
Range	0 to max int

Unused Timeout

The interval in seconds after which an unused or idle connection is discarded.

Set the Unused Timeout value higher than the Reap Timeout value for optimal performance. Unused physical connections are only discarded if the current number of connections not in use exceeds the Min Connections setting. For example, if the unused timeout value is set to 120, and the pool maintenance thread is enabled (Reap Time is not 0), any physical connection that remains unused for two minutes is discarded. Note that accuracy of this timeout, as well as performance, is affected by the Reap Time value. See Reap Time.

Information	Value
Data type	Integer
Units	Seconds
Default	1800
Range	0 to max int

Aged Timeout

The interval in seconds before a physical connection is discarded.

Set Aged Timeout to 0 supports active physical connections remaining in the pool indefinitely. Set the Aged Timeout value higher than the Reap Timeout value for optimal performance. For example, if the Aged Timeout value is set to 1200, and the Reap Time value is not 0, any physical connection that remains in existence for 1200 seconds (20 minutes) is discarded from the pool. Note that accuracy of this timeout, as well as performance, are affected by the Reap Time value. See Reap Time.

Information	Value
Data type	Integer
Units	Seconds
Default	0
Range	0 to max int

Purge Policy

Specifies how to purge connections when a stale connection or fatal connection error is detected.

Valid values are EntirePool and FailingConnectionOnly. Java EE Connector Architecture (JCA) data sources can have either option. WebSphere Version 4.0 data sources always have a purge policy of EntirePool.

Information	Value
Data type	String
Default	FailingConnectionOnly
Range	EntirePool All connections in the pool are marked stale. Any connection not in use is immediately closed. A connection in use is closed and throws a StaleConnectionException during the next operation on that connection. Subsequent getConnection requests from the application result in new connections to the database opening. When using this purge policy, there is a slight possibility that some connections in the pool are closed unnecessarily when they are not stale. However, this is a rare occurrence. In most cases, a purge policy of EntirePool is the best choice. FailingConnectionOnly Only the connection that caused the StaleConnectionException is closed. Although this setting eliminates the possibility that valid connections are closed unnecessarily, it makes recovery from an application perspective more complicated. Because only the currently failing connection is closed, there is a good possibility that the next getConnection request from the application can return a connection from the pool that is also stale, resulting in more stale connection exceptions.

Related:

Connection pooling

Configure a unified connection factory for the IBM MQ messaging provider

Configure a queue connection factory for the IBM MQ messaging provider

Configure a topic connection factory for the IBM MQ messaging provider

Mapping of administrative console panel names to command names and IBM MQ names

IBM MQ messaging provider queue connection factory settings

IBM MQ messaging provider topic connection factory settings