JVMHEAPS - less information for Liberty under CICS than for Z/OS Connect
Article ID: 238248
Updated On:
Products
Issue/Introduction
The JVMHEAPS command displays memory and heap-related storage allocation information for a JVM but this command displays less information for Liberty under CICS than for z/OS Connect.
For example:
JVMHEAPS display for Z/OS Connect:
Jobname ASID Application MemoryUsage
ZABC0001 0112 GSV_ZABC0001_040404B4 Heap Usage Total
ZABC0001 0112 GSV_ZABC0001_040404B4 Nursery-Allocate
ZABC0001 0112 GSV_ZABC0001_040404B4 Nursery-Survivor
ZABC0001 0112 GSV_ZABC0001_040404B4 Tenured-LOA
ZABC0001 0112 GSV_ZABC0001_040404B4 Tenured-SOA
JVMHEAPS display for Liberty under CICS:
Jobname ASID Application MemoryUsage
IKJ3A2ZB 0123 GSV_IKJ3A2ZB_04010DAB Heap Usage Total
IKJ3A2ZB 0123 GSV_IKJ3A2ZB_04010DAB Java heap
How to see Nursery and Tenured details on the JVMHEAPS displays for Liberty under CICS?
Environment
Release : 16.0
Component : SYSVIEW
Cause
The JVMHEAPS and JVMGC commands in SYSVIEW display information that is gathered from JVM MXBeans.
As a simple overview, SYSVIEW asks the JVM for the MXBeans and then SYSVIEW displays whatever the JVM returns.
The JVMBEANS command in SYSVIEW will show all of the beans in a JVM.
SYSVIEW does not influence the information reported on JVMHEAPS and JVMGC; SYSVIEW merely presents whatever the JVM gives back to SYSVIEW.
When it comes to memory specific MXBeans, which we display on JVMHEAPS, the memory pools returned by the JVM MXBeans can be influenced by several JVM arguments.
These arguments mainly revolve around the type of garbage collection policy specified by the -Xgcpolicy JVM argument. However, there is another JVM argument that is coming into play.
In older versions of CICS, when you run a JVMSERVER, the JVM argument -XX:+HeapManagementMXBeanCompatibility gets automatically specified. The JVMARGS command in SYSVIEW will display all the JVM arguments for a given JVM.
This argument tells the JVM to report memory specific MXBeans in a "compatibility mode", where the heap usage information is not split out into the more specific memory pools. It seems this argument no longer gets automatically specified in the newest version of CICS.Resolution
To resolve the issue it is necessary to update the jvm.profile file for the JVMSERVER and add the following line to remove the beans from being reported in a compatibility mode:
-XX:-HeapManagementMXBeanCompatibility
After restarting the CICS region, the JVMHEAPS will display similar information to the z/OS Connect server.
Additional Information
The following link talks about the JVM arguments from a CICS perspective:
Garbage collection and heap expansion
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