Tom Lane <t...@sss.pgh.pa.us> writes: > In principle you should be able to adjust the constant so that vmstat > shows about 50% CPU busy, and then enabling fadvise should improve > matters significantly.
I think in practice individual queries don't interleave much cpu with i/o work. A single random page fetch is 5ms which is an awful lot of cpu cycles to be sinking somewhere. In practice I think this is going to be single-digit percentages. Aside from big sorts and such which tend not to be interleaved with i/o the main time I've seen queries have a significant cpu load is when the data is mostly in cache. In which case prefetching would be hard pressed to help at all. We could construct a synthetic case but the main point of this feature is to make use of raid arrays that are currently going idle, not to pick up a few percentage points for single spindle systems. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's On-Demand Production Tuning -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
