Re: lchwaits, read aheads

In article <341968A8.4F9F@bloomberg.com>, "Art S. Kagel" <kagel@bloomberg.com> writes >Manoj wrote: >> >> All, >> >> Are there any guidelines for the below ? >> >> ixda-RA idx-RA da-RA RA-pgsused lchwaits >> 4398 29 27805 32188 55 > >This shows that the Informix read-ahead logic has prefetched 4398 index >leaves, 29 index nodes, and 27805 data pages for a total of 32232 >pages. You have actually used 32188 of those prefetched pages for a >Read-Ahead utilization rate of 99.86%. Pretty impressive. It shows >that you might benefit from increasing the Read-Ahead parameters in the >ONCONFIG file slightly. The latchwaits shows how often processes are >having to block (spinwaits are not counted here) because they cannot >get access to a shared memory resource. Unless the statistics were >cleared in the last minute or less (tbstat -z) 55 lchwaits is great. >I just cleared stats on one of our servers and about ten minutes later >we had 208 lchwaits with 432491 isamtot operations (just so you can >judge). > >Art S. Kagel The Informix Online Performance Tuning course recommends Read Ahead Utilisation should be 95% or greater. -- David Williams