Re: Amazon High I/O instances

[Sébastien Lorion <sl@xxxxxxxxxxxxxxxxxxxxx>]

You set shared_buffers way below what is suggested in Greg Smith book (25% or more of RAM) .. what is the rationale behind that rule of thumb ? Other values are more or less what I set, though I could lower the effective_cache_size and vfs.zfs.arc_max and see how it goes.

Sébastien

On Wed, Sep 12, 2012 at 7:24 PM, John R Pierce <pierce@xxxxxxxxxxxx> wrote:

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)

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




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