On Thu, Mar 1, 2012 at 9:57 AM, Jeff Janes <jeff.janes@xxxxxxxxx> wrote: > On Tue, Feb 28, 2012 at 3:46 PM, Stefan Keller <sfkeller@xxxxxxxxx> wrote: >> 2012/2/28 Claudio Freire <klaussfreire@xxxxxxxxx>: >>> >>> In the OP, you say "There is enough main memory to hold all table >>> contents.". I'm assuming, there you refer to your current system, with >>> 4GB memory. >> >> Sorry for the confusion: I'm doing these tests on this machine with >> one table (osm_point) and one country. This table has a size of 2.6GB >> and 10 million tuples. The other machine has to deal with at least 5 >> tables in total and will be hold more than one country plus routing >> etc.. > > What is your shared_buffers set to? 2.6GB is uncomfortably close to > 4GB, considering the computer has other things it needs to use memory > for as well. The real danger here is that the kernel will happily swap ut shared_buffers memory to make room to cache more from the hard disks, especially if that shared_mem hasn't been touched in a while. On a stock kernel with swappinness of 60 etc, it's quite likely the OP is seeing the DB go to get data from shared_buffers, and the OS is actually paging in for shared_buffers. At that point reading from kernel cache is MUCH faster, and reading from the HDs is still probably faster than swapping in shared_buffers. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
