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®.
The
-Xmx and
-Xss parameters
might need to be changed for the Gateway daemon.
- 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 256 KB with Java V7
31-bit, and 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.
The following values might need to increase for a CICS TS server.
- 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 Servers.
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 (128MB) is adequate
for an EXCI workload, it might be necessary to increase this to 256MB
or 512MB 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.