I wanted to follow up on my last blog entry about speeding up the DB2 database restore on an AIX machine. We did some more testing last night by enabling the jfs2 logging back to how it should be. The restore took only 5 minutes when it used to take 5 hours!
So we are very happy about this result. It’s obvious that the change to the kernel parameter MAXREQS from the default of 4096 to 7936 did the trick. If you saw my previous blog post, we are not sure why our 5 hour restores went down to 2.5 hours after disabling JFS2 logging. We are convinced it was an anomoly and had to do with other activity on the system during our test.
If you see any I/O contention on your AIX box, make sure and check out the value for MAXREQS.
>lsattr -E -l aio0 -a maxreqs
Make sure the result is at least 256 times the value for the DB CFG setting of NUM_IOSERVERS. If you have a machine with a number of CPU’s and DB2’s Automatic Tuning increased NUM_IOSERVERS to a high number (in our case it went to 31), it’s possible that the value of MAXREQS needs to be increased.