iostat and Rollback Segments

Running some testing thats simple purpose is to commit as frequently as possible and generate redo. Watching iostat I see redo showing 20% utilization. The volume containing rollback segment maxes out at around .8 MB per second and shows 100% utilization. I have moved the rollback segments around and tried different sizes. What I see is the same volume jump to 15 MB per second at times (i.e. copying an archive log), this can be sustained for 10-20 seconds or so. How come the very same volumes max out at .8 MB per second for rollback segments?

Also in playing around with rollback segment sizes I noticed dramatic differences in amount writen to the rollback segment in the writes column of v$rollstat.

The test runs at almost the exact same rate with all iterations of rollback segment sizes and placement. Disk always hits 100% on rollback segment volume but I see no waits on any rollback segments. Writes increases greatly based on RBS size but time to complete is always the same.

hum...?

Thanks,
Ethan Post Received on Thu Oct 04 2001 - 23:30:08 CDT