On Tue, 23 Aug 2005 10:10:45 -0700 (PDT) gokulnathbabu manoharan <[EMAIL PROTECTED]> wrote:
> Hi all, > > I like to know the caching policies of Postgresql. > What parameter in the postgresql.conf affects the > cache size used by the Postgresql? As far as I have > searched my knowledge of the parameters are > > 1. shared_buffers - Sets the limit on the amount of > shared memory used. If I take this is as the cache > size then my performance should increase with the > increase in the size of shared_buffers. But it seems > it is not the case and my performance actually > decreases with the increase in the shared_buffers. I > have a RAM size of 32 GB. The table which I use more > frequently has around 68 million rows. Can I cache > this entire table in RAM? increasing shared_buffers to a point helps, but after a certain threshold it can actually degree performance. > 2. work_mem - It is the amount of memory used by an > operation. My guess is once the operation is complete > this is freed and hence has nothing to do with the > caching. This is the amount of memory used for things like sorts and order bys on a per backend process basis. > 3. effective_cache_size - The parameter used by the > query planner and has nothing to do with the actual > caching. The instructs the query planner on how large the operating system's disk cache is. There isn't a built in cache, PostgreSQL relies on the operating system to cache the on disk information based on how often it is used. In most cases this is probably more accurate anyway. I wrote an article on PostgreSQL performance tuning that has links to several other related sites, you can find it here: http://www.revsys.com/writings/postgresql-performance.html --------------------------------- Frank Wiles <[EMAIL PROTECTED]> http://www.wiles.org --------------------------------- ---------------------------(end of broadcast)--------------------------- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
