Sun Java System Application Server 9.1 Performance Tuning Guide

Tuning JDBC Connection Pools

Set JDBC Connection Pool attributes with the Admin Console under Resources > JDBC > Connection Pools > PoolName. The following attributes affect performance:

Pool Size Settings

The following settings control the size of the connection pool:

Initial and Mimimum Pool Size

Size of the pool when created, and its minimum allowable size.

Maximum Pool Size

Upper limit of size of the pool.

Pool Resize Quantity

Number of connections to be removed when the idle timeout expires. Connections that have idled for longer than the timeout are candidates for removal. When the pool size reaches the initial and minimum pool size, removal of connections stops.

The following table summarizes pros and cons to consider when sizing connection pools.

Table 3–4 Connection Pool Sizing

Connection pool  



Small Connection pool 

Faster access on the connection table. 

May not have enough connections to satisfy requests. 

Requests may spend more time in the queue. 

Large Connection pool 

More connections to fulfill requests. 

Requests will spend less (or no) time in the queue 

Slower access on the connection table. 

Timeout Settings

There are two timeout settings:

Isolation Level Settings

Two settings control the connection pool’s transaction isolation level on the database server:

Avoid specifying Transaction Isolation Level. If that is not possible, consider setting Isolation Level Guaranteed to false and make sure applications do not programmatically alter the connections’ isolation level.

If you must specify isolation level, specify the best-performing level possible. The isolation levels listed from best performance to worst are:





Choose the isolation level that provides the best performance, yet still meets the concurrency and consistency needs of the application.

Connection Validation Settings

The following settings determine whether and how the pool performs connection validation.

Connection Validation Required

If true, the pool validates connections (checks to find out if they are usable) before providing them to an application.

If possible, keep the default value, false. Requiring connection validation forces the server to apply the validation algorithm every time the pool returns a connection, which adds overhead to the latency of getConnection(). If the database connectivity is reliable, you can omit validation.

Validation Method

Type of connection validation to perform. Must be one of:

  • auto-commit: attempt to perform an auto-commit on the connection.

  • metadata: attempt to get metadata from the connection.

  • table (performing a query on a specified table). Must also set Table Name. You may have to use this method if the JDBC driver caches calls to setAutoCommit() and getMetaData().

    Note –

    Because many JDBC drivers cache the results of these calls, they do not always provide reliable validations. Check with the driver vendor to determine whether these calls are cached or not.

Table Name

Table name to query when Validation Method is “table.”

Close All Connections On Any Failure

Whether to close all connections in the pool if a single validation check fails. The default is false. One attempt will be made to re-establish failed connections.