Connection pool settings
The path to configure connection pool settings depends on the type of resource, but generally you select an instance of the resource provider, then an instance of the resource type, then click Connection Pool. For example...Resources | JDBC Providers | JDBC_provider | Data Sources | data_source | Connection Pool.
Connection Timeout Interval, in seconds, after which a connection request times out and a ConnectionWaitTimeoutException is thrown.
The wait is necessary when 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, 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).
Data type Integer Units Seconds Default 180 Range 0 to max int
Max Connections Maximum number of physical connections that you 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.
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.
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 you 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.
Data type Integer Default 1 Range 0 to max int
Reap Time 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.
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 which timeout due to non-zero timeout values are discarded.
Data type Integer Units Seconds Default 180 Range 0 to max int
Unused Timeout 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 for more information.
Data type Integer Units Seconds Default 1800 Range 0 to max int
Aged Timeout Interval in seconds before a physical connection is discarded.
Setting 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. The accuracy of this timeout, as well as performance, are affected by the Reap Time value. See Reap Time for more information.
Data type Integer Units Seconds Default 0 Range 0 to max int
Purge Policy How to purge connections when a stale connection or fatal connection error is detected. Valid values are EntirePool and FailingConnectionOnly. JCA data sources can have either option.
Data type String Default EntirePool 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.
The Connection pretest function attempts to insulate an application from pooled connections that are not valid. When a backend resource, such as a database, goes down,, pooled connections that are not valid might exist in the free pool. This is especially true when the purge policy is failingConnectionOnly; in this case, the failing connection is removed from the pool. Depending on the failure, the remaining connections in the pool might not be valid.