On Dec 5, 2007 12:53 PM, Kenneth Marshall <[EMAIL PROTECTED]> wrote: > On Wed, Dec 05, 2007 at 12:29:13PM -0800, David Rees wrote: > > > > It would be interesting to find out why PostgreSQL was underperforming > > for you. What kind of tuning have you tried? I suspect that the new > > async commit options in 8.3 would improve things a lot. > > The performance problem was caused by the I/O pattern degrading to > completely random I/O over time. The initial performance or the > performance immediately after a CLUSTER of the tables was easily > as good as the MySQL backend (~20 messages/sec). The steady state > (~6 messages/sec) did not provide sufficient headroom for our > system to allow for clearing out a backlog following any type > of delivery problem. The async commit option in 8.3 will help, but > I expect the HOT updates to be the real win, by allowing the tables > to maintain their cluster order over time. We will report back once > we have some test data.
Thanks, that is one performance concern I have with PostgreSQL frequently updated/inserted tables/indexes over time, they tend to get fragmented. I suspect that using XFS along with regular runs of xfs_fsr would take care of any fragmentation issues, but also agree that the HOT patches should also help significantly. Looking at the tables/indexes on one of my systems reveals fairly significant table/index bloat. -Dave
