Gateway Daemon Memory workspace

The Gateway Daemon Memory workspace provides detailed information about memory usage in CICS Transaction Gateway so that you can generate alerts before Out-Of-Memory (OOM) exceptions occur, and for trending and capacity planning.

The Gateway Daemon Memory workspace is built from attributes provided by the CICSTG Gateway Daemon Memory attribute group, the CICSTG Connection Manager Threads attribute group, and the CICSTG Worker Threads attribute group. The workspace contains this information:

  • The 31-bit Native Memory Statistics subpanel or view shows the extended user private storage (31-bit) usage in the address space.
  • The 31-bit JVM Memory Statistics subpanel or view shows information on JVM 31-bit heap usage and Garbage Collection (GC) information.
  • The 64-bit Memory Statistics subpanel or view shows the effective MEMLIMIT for the CICS TG address space and the current amount of used 64-bit or above the bar memory.

The amount of memory used in a CICSTG address space may increase gradually, leading to Out-Of-Memory (OOM) exception. Besides the user application misbehaviors, this condition may occur if there were too many threads allocated. For this reason, Connection Manager and Worker thread statistics should be considered.

These three subpanels help you address specific memory issues:

  • Problem: The JVM heap size may be unnecessarily too large or too small.

    Advice: The 31-bit JVM Memory Statistics subpanel includes information to help to determine the optimal JVM heap size.

  • Problem: Another reason for OOM condition may be that the REGION size (as specified in the JCL) is too small.

    Advice: The 31-bit Native Memory Statistics subpanel includes information to help determine whether REGION size will have to be increased.

  • Problem: there may be insufficient above the bar memory.

    Advice: The 64-bit Memory Statistics subpanel should help to determine whether enough above the bar memory is available to handle the workload.

The Used 31-bit memory percentage is calculated based on the above two metrics (available and currently allocated memory).

The Gateway daemon JVM heap size after the last garbage collection is the amount of occupied (currently in-use) 31-bit heap memory. This metric is used to calculate heap occupancy – or the used JVM heap size percentage – based on the maximum size of JVM heap in the Gateway daemon.

The total amount of native memory used by the Gateway daemon increases per thread. Two thread subpanels are displayed at the bottom of the Gateway Daemon Memory workspace to make it more convenient to view thread information:
  • The Connection Manager Threads Summary subpanel or view provides detailed information about the current CICS® TG's allocation and use of Connection Manager threads.
  • The Worker Threads Summary table subpanel or view provides detailed information about the selected CICS TG's allocation and use of Worker threads.

For more information on CICS Transaction Gateway statistics, see Tuning the Gateway to avoid out of memory conditions.