Starting the shared class cache

You can start the shared class cache in three ways:
  1. You can set the shared class cache to start at CICS initialization, by setting the JVMCCSTART system initialization parameter to YES. (This setting also enables autostart.)
  2. You can enable autostart for the shared class cache. If you enable autostart, the shared class cache is started automatically as soon as CICS receives a request to run a Java™ application in a JVM whose profile requires the use of the shared class cache. When you first use CICS, autostart is enabled by default. If you have disabled autostart, there are three ways to enable it again:
    1. To enable autostart for the next CICS execution, set the JVMCCSTART system initialization parameter to either YES, or AUTO. YES makes the shared class cache start at CICS initialization, and also enables autostart. AUTO just enables autostart, and does not make the shared class cache start at CICS initialization.
    2. When CICS is running, use the CEMT SET CLASSCACHE AUTOSTARTST command (or the equivalent EXEC CICS command) to enable autostart.
    3. If you are terminating (phasing out, purging or forcepurging) the shared class cache, use the AUTOSTARTST option on the CEMT PERFORM CLASSCACHE command (or the equivalent EXEC CICS command) to enable autostart.
    Use the CEMT INQUIRE CLASSCACHE command (or the equivalent EXEC CICS command) to find out the current status of autostart for the shared class cache. When you change the autostart status of the shared class cache while CICS is running, subsequent CICS restarts use the most recent setting that you made using the CEMT SET CLASSCACHE command or the CEMT PERFORM CLASSCACHE command (or the equivalent EXEC CICS commands), unless the system is INITIAL or COLD started, or the JVMCCSTART system initialization parameter is specified as an override at startup. In these cases, the setting from the system initialization parameter is used.
  3. When CICS is running, if you have disabled autostart, or if autostart is enabled but no JVM has yet required the shared class cache, you can start the shared class cache manually by entering a CEMT PERFORM CLASSCACHE START command (or the equivalent EXEC CICS command). When you use this command, you can specify the size of the shared class cache (CACHESIZE option), and the profile that is used for the master JVM that initializes the shared class cache (PROFILE option).
If your CICS system is WARM or EMERGENCY started, and the shared class cache was started when the system shut down, then it is started at CICS initialization. This happens whatever the autostart status is, unless the JVMCCSTART system initialization parameter is specified as an override at startup, in which case the behaviour specified by the system initialization parameter is used.

When you start the shared class cache by an explicit command or by the autostart feature, there is a short delay while the master JVM initializes the shared class cache. If CICS receives requests during this period for worker JVMs that require the use of the shared class cache, the requests wait until the startup process is complete and the shared class cache is ready.

When you have decided how and when you normally prefer the shared class cache to start in your CICS system, use the JVMCCSTART system initialization parameter to set the normal behaviour for the shared class cache. The CICS default setting for the JVMCCSTART system initialization parameter is AUTO. This setting means that when you start CICS, the shared class cache does not start up immediately. However, autostart is enabled, so the shared class cache starts automatically when the first worker JVM requires it. This is the situation when you first use CICS.

If you prefer the shared class cache to start up during CICS initialization, so that it is ready and waiting when the first worker JVM requires it, set the JVMCCSTART system initialization parameter to YES. This setting enables autostart, so if you stop the shared class cache, it starts again automatically when the first worker JVM requires it.

If you prefer the shared class cache not to start at all until you enter a specific command, set the JVMCCSTART system initialization parameter to NO. This setting disables autostart, so when you want to start the shared class cache, you need either to enter a CEMT PERFORM CLASSCACHE START command (or the equivalent EXEC CICS command), or to enable autostart by one of the methods described above. If a Java program needs to run in a JVM that uses the shared class cache, and the shared class cache has not been started, and autostart is disabled, then the program cannot run.