On Sat, 15 Dec 2007, okparanoid@free.fr wrote:
> First when i run htop i see that the memory used is never more than 150 MB.
> I don't understand in this case why setting shmall and shmmax kernel's
> parameters to 16 GB of memory (the server has 32 GB) increase the rapidity of
> the transaction a lot compared to a shmall and shmax in (only) 2 GB ?!
The kernel parameters provide an upper limit for how much memory
PostgreSQL can allocate, but by themselves they don't actually request
more memory. There is a configuration parameters called shared_buffers
that is the main thing to adjust. Since you say you're new to this, see
http://www.westnet.com/~gsmith/content/postgresql/pg-5minute.htm for the
first set of things you should be adjusting.
If you're doing lots of updates, you'll need to increase
checkpoint_segments as well. Once you get the memory allocated and
checkpoint parameters in the right range, at that point you'll be prepared
to look into transaction grouping and application issues in that area.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
