On Tue, 20 Oct 2009, Waldomiro wrote:
So, I put in sharedbuffers the same size my two biggest tables, which are the most read too. 11 GB + 4 GB. total shared buffers = 15 GB
That seems quite reasonable. The rest of the unused RAM in the server is going to be used by the operating system cache, which works as a layer on top of shared_buffers. There are a couple of problems with giving most of your RAM to the database directly. The three most obvious ones are that it doesn't leave anything for other applications, the PostgreSQL shared_buffers design isn't optimized for really large amounts of RAM, and memory given to shared_buffers has to be involved in the database checkpoint computations--whereas OS cached buffers are not.
After that I put 100 MB to each expected user, 300 * 100 MB = 30 GB So, I used only 30 GB + 15GB = 45 GB total RAM
Leaving 19GB for the operating system to cache things with. It's not going to be unused. That's quite reasonable, and more flexible as far as what the server can accomplish than had you given more memory to shared_buffers. It might even perform better--there's been some evidence that shared_buffers starts to degrade going much beyond the 10GB range anyway.
Your starting configuration seems fine to me, I would suggest getting your application running and measure actual memory use before tweaking anything further.
-- * Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
