I'd like to thank Mike Russell for writing most of this blog article. Mike works on the IBM i Work Management team and was responsible for the changes described in this blog. Thanks, Mike!
Some time ago, I wrote about the job table and permanent job structures in IBM i Job Structures (January 11, 2011). That article reviewed the job table and also discussed compressing the job table.
In the IBM i 7.1 release, IBM restructured the processing of the job table cleanup that at happens during an abnormal IPL as well as the processing that is done when job tables are compressed. The job table cleanup IPL step is also known as Work Control Block Table cleanup (C900 2C40) IPL step.
Prior to 7.1, the job table was processed by one thread during the IPL step; when the job table became large, it could take this one thread quite some time to process all the entries in the job table. In the 7.1 release, this single-threaded processing was changed to be multi-threaded. This change decreases the time the system is unavailable after an unexpected termination as well as when the job tables are compressed during an IPL.
This new news is that this function is now available for the 6.1 release with PTF SI48088.
The performance improvement is seen on systems with a large number of entries in the job table. You can use the Display Job Table (DSPJOBTBL) command to view the number of entries on your system. The Change IPL Attributes (CHGIPLA) command allows you to influence how much cleanup is done at IPL with the Check job tables (CHKJOBTBL) and Compress job tables (CPRJOBTBL) parameters. How the system powered down is the other influence on how much cleanup is done at IPL. You can check the history on your system to see if you have had any recent abnormal IPLs with the Display Log command: DSPLOG PERIOD((*AVAIL *BEGIN)) MSGID(CPI0990 CPI091D)
There is also a 7.1 release PTF (SI48454) that includes a minor performance improvement for job table cleanup and a correction for the IPL status estimated time remaining:
You should not have to run job table cleanup or compression very often, but it is one of those things that when it is necessary, time is most likely important as well. This was an important fix for reducing IPL time in the 7.1 release and it's now available on 6.1.