When running the Gateway daemon under load and using IPIC connected servers, you might need to increase the size of the JVM heap for the Gateway daemon if performance problems are encountered.
When running with container sizes greater than 1 MB, it might be necessary to increase the JVM resources for the Gateway daemon and CICS®.
- Increase the maximum amount of heap memory available to the Gateway daemon using the -Xmx parameter. Failure to increase the heap could result in a JVM exception as a result of a java.lang.OutOfMemory error. Be aware that increasing the maximum heap size will reduce the amount of available process memory and therefore the number of Java™ threads that can be created. See Tuning the Gateway to avoid out-of-memory conditions for more information.
- Increase the stack available to the Java threads using the -Xss parameter. The default value of -Xss is 512 KB with Java V7 64-bit. The default settings can be found in the Java Diagnostics Guide. Running with the a 256 KB setting for -Xss is suitable for container sizes up to 50 MB. Failure to increase the Java thread stack size might result in a JVM exception as a result of a java.lang.StackOverflowError.
For information on setting the -Xmx and -Xss parameters, refer to Setting Gateway daemon JVM options.
- MEMLIMIT - Is the limit for above-the-bar storage for the CICS server. Abend codes AITJ and APCG are an indication that MEMLIMIT might be too small.
- EDSALIM - The EDSALIM system initialization parameter specifies the upper-limit of the total amount of storage within which CICS can allocate the individual extended dynamic storage areas (EDSAs) that reside above 16 MB but below 2 GB. Abend code AIPE is an indication that the EDSALIM memory might be too small.
For more information about abend codes and their meaning, see CICS Transaction Server Diagnostics reference.
For information about how statistics might indicate that a JVM is short of heap storage see JVM stress causing poor performance in the Gateway daemon.
While the default maximum heap size (128 MB) is adequate for an EXCI workload, it might be necessary to increase this to 256 MB or 512 MB for an IPIC workload. Ensure that the region size is increased accordingly to match any increases in heap size, otherwise the Gateway daemon might fail with a java.lang.OutOfMemory error. See Configuring Java shared classes.