Configuring WebLogic Server Environments
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WebLogic Server 9.0 has new features for detecting, avoiding, and recovering from overload conditions. WebLogic Server's overload protection features help prevent the negative consequences—degraded application performance and stability—that can result from continuing to accept requests when the system capacity is reached.
When system capacitiy is reached, if an application server continues to accept requests, application performance and stability can deteriorate. The following sections demonstrate how you can configure WebLogic Server to minimize the negative results of system overload.
In WebLogic Server 9.0, all requests, whether related to system administration or application activity—are processed by a single thread pool. An administrator can throttle the thread pool by defining a maximum queue length. Beyond the configured value, WebLogic Server will refuse requests, except for requests on administration channels.
Note: Administration channels allow access only to administrators. The limit you set on the execute length does not effect administration channel requests, to ensure that reaching the maximum thread pool length does not prevent administrator access to the system. To limit the number of administration requests allowed in the thread pool, you can configure an administration channel, and set the Max Open Socket Value for the channel.
When the maximum number of enqueued requests is reached, WebLogic Server immediately starts rejecting:
Throttle the thread pool by setting the Max execute queue Length field in the Administration Console. (See Environments > Servers > Threads and select an execute queue.) The default value of this field is 65536.
An administrator can configure Work Managers to manage the thread pool at a more granular level, for sets of requests that have similar performance, availability, or reliability requirements. A Work Manager can specify the maximum requests of a particular request class that can be queued. The maximum requests defined in a Work Manager works with global thread pool value. The limit that is reached first is honored.
See Using Work Managers to Optimize Scheduled Work.
An administrator can limit the number of active HTTP sessions based on detection of a low-memory condition. This is useful in avoiding out of memory exceptions.
WebLogic Server refuses requests that create new HTTP sessions after the configured threshold has been reached. In a WebLogic Server cluster, the proxy plug-in redirects a refused request to another Managed Server in the cluster. A non-clustered server instance can re-direct requests to alternative server instance.
The servlet container takes one of the following actions when maximum number of sessions is reached:
You set a limit for the number of simultaneous HTTP sessions in the deployment descriptor for the Web Application. For example, the following element sets a limit of 12 sessions:
<session-descriptor>
<max-in-memory-sessions>12</max-in-memory-sessions>
</session-descriptor>
Administrators can configure WebLogic Server to exit upon an out of memory exception. This feature allows you to minimize the impact of the out of memory condition—automatic shutdown helps avoid application instability, and you can configure Node Manager or another HA tool to automatically restart WebLogic Server, minimizing down-time.
You can configure this using the Administration Console, or by editing the following elements in config.xml:
<overload-protection>
<panic-action>system-exit</panic-action>
</overload-protection>
For more information, see the attributes of the OverloadProtectionMBean.
WebLogic Server checks for stuck threads periodically. If all application threads are stuck, a server instance marks itself failed, if configured to do so, exits. You can configure Node Manager or a third-part high-availability solution to restart the server instance for automatic failure recovery.
You can configure these actions to occur when not all threads are stuck, but the number of stuck threads have exceeded a configured threshold,
For more information, see the attributes of the OverloadProtectionMBean.
The following sections describe WebLogic Server features that aid in determining and reporting overload conditions.
WebLogic Server 9.0 has a new health state—OVERLOADED
—which is returned by the ServerRuntimeMBean.getHealthState()
when a server instance whose life cycle state is RUNNING
becomes overloaded. This condition occurs when Work Manager capacity is exceeded or as a result of low memory.
The server instances health state returns to OK
after the overload condition passes. An administrator can suspend or shut down an OVERLOADED
server instance.
When WebLogic Server exits it returns an exit code. The exit codes can be used by shell scripts or HA agents to decide whether a server restart is necessary. See WebLogic Server Exit Codes and Restarting After Failure in Managing Server Startup and Shutdown.
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