Performance Advice from a Mysterious Friend, Part 6
April 23, 2008 Ted Holt
This is the last of the performance tips that I received from one of your fellow readers. I hope you’ve enjoyed the previous tips and found some of them useful as well.
Today’s advice: “Increase the journal recovery ratio from the default of 50,000 to 250,000.”
IBM’ers Larry Youngren and Chris Kindinger provide a thorough discussion of this topic at http://www.redbooks.ibm.com/abstracts/tips0625.html”. Although the discussion centers around V5R4, they also provide information for V5R3 and V5R2.
The journal recovery ratio has to do with the IPL process. The journal recovery ratio’s purpose is to limit the number of journal entries that must be reapplied to the database in the event of a system crash when the contents of main memory could not be written to disk. Youngren and Kindinger point out that the default value of 50,000 was set when machinery was much slower than current systems and when the system recovery algorithms were not as good as the ones available today. Hardware and software advances are a good indication that the default value is probably not the most effective setting these days.
To increase the journal recovery ratio, use the Change Journal (CHGJRN) command.
CHGJRN . . . JRNRCYCNT(250000)
Users of V5R3 and V5R2 can find other instructions in the Larry Youngren and Chris Kindinger’s article linked above.