Questions on capturing garbage collection data in WebSphere Message Broker

Technote (FAQ)


Q1. How can you capture GC (garbage collection) activity for individual Execution Groups?
Q2. How can you capture GC activity for all the Execution Groups in a broker together?


A1. Starting with WebSphere Message Broker V6.1.0.8 and V7.0.0.1 (and in subsequent fix packs), you can run the following command to capture GC activity at an Execution Group level:
mqsichangeproperties <broker> -e <EG> -o ComIbmJVMManager -n jvmSystemProperty -v"-verbose:gc -Xverbosegclog:/tmp/gc.trc"

A2. The GC activity at the broker level can be captured in one of the following ways:

a. You can export the following environment variable in the broker service Id's profile to capture the GC information for all the Execution Groups in a broker:
export IBM_JAVA_OPTIONS=-Xverbosegclog:<directory with plenty of space>/gc.out
Restart the broker to pick up the above environment variable.
This will log the GC information in the file gc.out

b. The garbage collection activity may be captured by setting the following environment variable:
export MQSIJVERBOSE=-verbose:gc
Restart the broker to pick up the above environment variable

This will log the GC information in stdout/stderr files located in:
<C:\Documents and Settings\All Users\Application Data\IBM\MQSI\components> \<broker name>\<EG UUID>\ (for Windows)
/var/mqsi/components/<broker name>/<EG UUID>/ (for UNIXes)

The Java™ Runtime environment takes the values for its initial, maximum and current heap sizes to calculate how frequently garbage collection needs to be driven. If a large maxJVMHeapSize is set, then this means that garbage collection will be driven less frequently within the broker's JVM.

Historical Number


Product Alias/Synonym

WMB MB Message Broker MQ Integrator WBIMB WBI-MB MQSI WMQI

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Document information

More support for:

WebSphere Message Broker
Execution Group

Software version:

6.1, 7.0, 8.0

Operating system(s):

AIX, HP-UX, Linux, Solaris, Windows

Reference #:


Modified date:


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