Just curious ... has anyone tried using a ram disk as the PG primary and DRBD as the means to make it persistent? On Mar 1, 2012 11:35 AM, "Scott Marlowe" <scott.marl...@gmail.com> wrote:
> On Thu, Mar 1, 2012 at 9:57 AM, Jeff Janes <jeff.ja...@gmail.com> wrote: > > On Tue, Feb 28, 2012 at 3:46 PM, Stefan Keller <sfkel...@gmail.com> > wrote: > >> 2012/2/28 Claudio Freire <klaussfre...@gmail.com>: > >>> > >>> 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@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance >
