Sun Microsystems Sun GlassFish Enterprise Server 2.1 Tuning Manual page 79

Idle Timeout: Maximum time in seconds that a connection can remain idle in the pool.
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After this time, the pool can close this connection. This property does not control
connection timeouts on the database server.
Keep this timeout shorter than the database server timeout (if such timeouts are configured
on the database), to prevent accumulation of unusable connection in Enterprise Server.
For best performance, set Idle Timeout to zero (0) seconds, so that idle connections will not
be removed. This ensures that there is normally no penalty in creating new connections and
disables the idle monitor thread. However, there is a risk that the database server will reset a
connection that is unused for too long.
Isolation Level Settings
Two settings control the connection pool's transaction isolation level on the database server:
Transaction Isolation Level: specifies the transaction isolation level of the pooled database
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connections. If this parameter is unspecified, the pool uses the default isolation level
provided by the JDBC Driver.
Isolation Level Guaranteed: Guarantees that every connection obtained from the pool has
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the isolation specified by the Transaction Isolation Level parameter. Applicable only when
the Transaction Isolation Level is specified. The default value is true.
This setting can have some performance impact on some JDBC drivers. Set to false when
certain that the application does not change the isolation level before returning the
connection.
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:
1. READ_UNCOMMITTED
2. READ_COMMITTED
3. REPEATABLE_READ
4. SERIALIZABLE
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.
Chapter 3 • Tuning the Enterprise Server
Pool Resize Quantity
79