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for z/OS
If it is necessary to obtain a dump of an address space in WebSphere
Application Server for z/OS environment when you are experiencing a hang
or loop situation:
- Understand the System Resource Considerations described below.
- Verify that your DUMP dataset is large enough for the dump you are
taking.
- Recreate the problem (the reason why you need to take the dump).
- If this is a possible LOOP or HIGH CPU condition, consider turning on
BRANCH tracing.
- Issue the DUMP command, using the example in this technote.
- Verify that you see message IEA611I in the SYSLOG. This message
indicates that a Complete dump was taken. If a Partial dump
was taken, use the message description contained in WebSphere
Application Server V4.0.1 for z/OS: Messages and Diagnosis or the V5
WebSphere Application Server Information Center to decode the SDRSN
codes and correct any problems you might have.
- Turn off BRANCH tracing if previously enabled.
System resource considerations
CPU utilization
This depends on the size and number of address spaces you are dumping. It
is hard to quantify the impact. Think in terms of the size of your typical
dumps and how long they take. This should give you a feel for the length
of time required to take this dump. You can use SDSF to approximate the
size of the dump.
Paging
During DUMP processing a copy of all the pages in an address space is made
in virtual storage. The amount of virtual storage required depends on the
size of the address spaces you are dumping. If your dump is large,
consider the following:
MAXSPACE setting
This setting limits the amount of virtual storage all dumps currently
being processed can occupy. If this value is exceeded, the result is a
Partial Dump, which is virtually useless. The default setting is 500 meg,
which is small for a WebSphere Application Server for z/OS environment.
Issue the following MVS command to display your existing MAXSPACE setting:
D D,ST
Then issue MVS command, CHNGDUMP, to increase this setting, if
necessary. This command is described in z/OS V1R4.0 MVS SYSTEM
COMMANDS, SA22-7627.
For example, to increase the MAXSPACE setting to 2 gig, issue the
following command:
CD SET,SDUMP,MAXSPACE=2000M
PAGE space setting
These dumps are usually large, anywhere from 500 meg to 1 gig, on an
average. They can be significantly larger if you are dumping several
address spaces. Most of this storage ends up in your PAGE datasets.
MAXSPACE is there to protect your system from running out of PAGE
datasets. If you raise the MAXSPACE, be sure you have the PAGE datasets to
support the same value.
Dump dataset size
If your dataset is not large enough, the result is a partial dump. Look
for message IEA611I.
DUMP command
In the WebSphere Application Server for z/OS environment, the OMVS address
space and its DataSpaces is usually dumped. Following is an example of
such a dump:
DUMP COMM=(Descriptive name for this Webserver dump)
R rn,sdata=(CSA,SQA,RGN,TRT,GRSQ,LPA,LSQA,SUM,NUC,PSA),CONT
R rn,jobname=(OMVS,server_name),CONT
R rn,dspname=('OMVS'.*),END
For a listing of technotes, downloads and educational materials
specific to High CPU, search the WebSphere Application Server for z/OS support
site.
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