Re: Read Ahead Pages, etc.

Dianne Pendleton wrote: > > Hi. I have looked in the manuals and cannot find the calculation I am looking > for. Somewhere, I had seen a simple calculation for determining if your RA > parameters were set well. Here is the last line from an onstat -p: > > ixda-RA idx-RA da-RA RA-pgsused > 5366028 0 4461898 9773662 > > > You are supposed to add and/or subtract these numbers in a particular way and I > think the goal was to be close to zero. Exactly. The calulation is: ixda-RA + idx-RA + da-RA ~= RA-pgsused or (ixda-RA + idx-RA + da-RA) - RA-pgsused ~ 0 If the second result is positive then your RA parameters are set too high. Obviously small positive values are just fine but a large descrepancy (more than a few percent of RA-pgsused) should be avoided as wasting resources and forcing buffers to thrash (reduced read cache%). I've never seen this calculation go negative so a result of zero MAY indicate that you can take advantage of more readahead, or it MAY indicate that you have hit on the PERFECT values for the RA parameters. Art S. Kagel