20.1.4 Connection pool clustering operations

(1) Suspending a connection pool

You can block and suspend a member connection pool. If you execute suspend, a member connection pool is blocked and suspended.

When a J2EE application sends a connection request to the root resource adapter, no connection request is sent to a blocked or suspended member connection pool.

You suspend the member connection pool in the following cases:

• When an error occurs in a database node

• When maintenance is performed for a database node

Note that the suspension methods include the following two methods:

• Auto-suspension

• Manual suspension

  Reference note

  With the suspension processing, the connections that the J2EE application has finished using are destroyed, all the connections in the connection pool are destroyed, and then the connection pool is suspended. When a network error or a database node error occurs, a connection is destroyed after waiting for the network to timeout, so the processing from blocking to suspending the connection pool might take time.

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(2) Restarting a connection pool

You can restart a suspended member connection pool. When the J2EE application makes a connection request to the root resource adapter, the connection requests are now sent to the restarted member connection pool again.

Note that to restart a connection pool, the number of unused connection management threads must be equal to or more than the maximum number of connections in the connection pool.

You restart the connection pool in the following cases:

• When the database node error is recovered

• When the maintenance of the database node finishes

The restart methods include the following two methods:

• Auto-restart

• Manual restart

  Reference note

  • If the number of unused connection management threads becomes equal to the maximum number of connections in the connection pool when the connection pool is stopped, a message is output. When the execution of the cjresumepool command fails, check the displayed message and then re-execute the command.

  • When the connection pool warming up functionality is enabled, the member connection pool starts after the minimum number of connections defined in the connection pool settings is pooled. If an attempt to generate a connection fails while the connections are being pooled, the member connection pool returns to the suspended state. Also, if the connection pool warming up functionality is disabled, the member connection pool starts immediately.

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(3) States of the connection pool

A connection pool state only exists for the member connection pools. Note that the connection pool state is maintained even after you restart the J2EE server and resource adapter.

You can check the state of the member connection pool with the following methods. When you execute manual suspension or manual restart, check the connection pool state before you execute the commands.

• cjlistrar command

  The cjlistrar command outputs the names and states of all the deployed resource adapters to the standard output. If you specify -clusterpool, you can also display the states of the member connection pools.

  For the command details, see cjlistrar (list resource adapters) in the uCosminexus Application Server Command Reference Guide.

• cjlistpool command

  The cjlistpool command displays the connection pool information. The command can also display the states of the member connection pools for the member resource adapters. For details on examples of displaying the connection information of a member resource adapter, see the manual uCosminexus Application Server Common Container Functionality Guide.

  For the command details, see cjlistpool (list connection pools) in the uCosminexus Application Server Command Reference Guide.

This section describes the states of the member connection pools.

The state of the member connection pool is maintained even if you restart the J2EE server and member resource adapter. For the procedure for checking the connection pool states, see 20.1.5(1) Checking the connection pool state.

Note that the connection pools other than those for the member resource adapters do not have a state.

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(4) How to select a connection pool

When the J2EE application sends a connection request to the root resource adapter, one member connection pool is selected. The method by which the member connection pool is selected at this time is the round-robin method.

The connection pool that is selected is a member connection pool with the Start status. A member connection pool that has free connections is selected on priority.

However, if only a member connection pool with depleted connections is available, the connection request changes to pending. Furthermore, if a timeout occurs in a pending connection, the connection cannot be obtained. Also, if a connection pool is blocked when a connection request is pending, the connection request is restarted and an attempt is made to obtain a connection from the member connection pool that is next in the priority order. If a connection cannot be obtained from any of the member connection pools, the attempt to obtain the connection fails.

Note that if there is a connection request when a member connection pool with the Start status does not exist, the attempt to obtain the connection fails.

To specify the maximum size of each member connection pool, use the following guideline:

Maximum-size-of -the-member-connection-pool-(number) = Maximum-number-of-concurrent-connections-permitted-for-the-system / number-of-database-nodes

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