Re: Amazon High I/O instances

On 09/12/12 4:03 PM, Sébastien Lorion wrote:
> I agree 1GB is a lot, I played around with that value, but it hardly
> makes a difference. Is there a plateau in how that value affects query
> performance ? On a master DB, I would set it low and raise as
> necessary, but what would be a good average value on a read-only DB
> with same spec and max_connections ?

a complex query can require several times work_mem for sorts and hash
merges. how many queries do you expect to ever be executing
concurrently? I'll take 25% of my system memory and divide it by
'max_connections' and use that as work_mem for most cases.

on a large memory system doing dedicated transaction processing, I
generally shoot for about 50% of the server memory as disk cache, 1-2GB
as shared_buffers, 512MB-2GB as maintenance_work_mem, and 20-25% as
work_mem (divided by max_connections)

--
john r pierce N 37, W 122
santa cruz ca mid-left coast