Windows 2008R2
OpenEdge 10.2B SP8
When the backup is not running, the buffer hit ratio is approx 99.99% and OS-Reads is approx 10.
But when we run an online backup, the buffer hit ratio varies from 75% to 8% and back (several times) andt the OS-Reads is approx 30.000.
We use the following command:
call probkup online <dbname> <backup name> -com -verbose -Bp 10
Before the backup we delete the backup file first.
When the backup is completed, the buffer hit ration is back to 99.99% after a few minutes and the OS-Reads is dropping to aprprox 10.
What can we do to keep the buffer hit ratio as high as possible during the online backup?
Just stop worry about the buffer hit ratio. ;-) Probably it should not count that db accesses for any types of the private buffers but it does.
Just stop worry about the buffer hit ratio. ;-) Probably it should not count that db accesses for any types of the private buffers but it does.
keep doing what you are doing.
the numbers look bad because the backup has to read every single data block below the highwater mark. that makes the hit ratio look low (and it is low, but only for the backup). with Bp 10, performance degradation is minimized and the impact on users is as low as it can be.
Like George says.. don't focus on the buffer hit percentage. Focus on the actual performance impact. Many metrics can be misleading and buffer hits is included in that list.
Are you having performance problems during the backup? If not then just ignore the drop in hit ratio and move on.
If you do have performance problems post more details about your hardware (memory and disk config), database size, how long the backup takes and what kind of performance issues (reads, writes, both) you are running into.
We had a problem with the backup (it was slow), but this was due to the task scheduler in Windows 2008R2 (priority change from 5 to 7). But during our investigations we notice that the buffer hit ratio was changing. The users didn't complaint about it. But I was curious if this was a problem or not.
Thanks for replying.