On Tue, 2006-11-14 at 09:17 -0500, Merlin Moncure wrote: > On 11/14/06, Cosimo Streppone <cosimo@xxxxxxxxxxxx> wrote: > > I must say I lowered "shared_buffers" to 8192, as it was before. > > I tried raising it to 16384, but I can't seem to find a relationship > > between shared_buffers and performance level for this server. > > My findings are pretty much the same here. I don't see any link > between shared buffers and performance. I'm still looking for hard > evidence to rebut this point. Lower shared buffers leaves more > memory for what really matters, which is sorting. In 8.0 there is a performance issue such that bgwriter will cause a performance problem with large shared_buffers setting. That in itself could lead to some fairly poor measurements of the value of shared_buffers. In 7.4 and prior releases setting shared_buffers higher was counter productive in many ways, so isn't highly recommended. In general, setting shared_buffers higher works for some workloads and doesn't for others. So any measurements anybody makes depend upon the workload and the size of the database. The more uniformly/randomly you access a large database, the more benefit you'll see from large shared_buffers. 8.1 benefits from having a higher shared_buffers in some cases because it reduces contention on the buffer lwlocks; 8.2 solves this issue. Even in 8.2 ISTM that a higher shared_buffers setting wastes memory with many connected users since the PrivRefCount array uses memory that could have been used as filesystem cache. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com
