Re: effective_cache_size on 32-bits postgres

On Mon, Mar 18, 2013 at 3:47 PM, Kevin Grittner <kgrittn(at)ymail(dot)com> wrote:
> Rodrigo Barboza <rodrigombufrj(at)gmail(dot)com> wrote:
>
>> So setting this as half of ram, as suggested in postgres tuning
>> webpage should be safe?
>
> Half of RAM is likely to be a very bad setting for any work load.
> It will tend to result in the highest possible number of pages
> duplicated in PostgreSQL and OS caches, reducing the cache hit
> ratio. More commonly given advice is to start at 25% of RAM,
> limited to 2GB on Windows or 32-bit systems or 8GB otherwise. Try
> incremental adjustments from that point using your actual workload
> on you actual hardware to find the "sweet spot". Some DW
> environments report better performance assigning over 50% of RAM to
> shared_buffers; OLTP loads often need to reduce this to prevent
> periodic episodes of high latency.

He's asking about effective_cache_size. You seem to be talking about
shared_buffers.

Real question behind this all, is whether the e_c_s GUC is 32-bit on
32-bit systems. Because if so, it ought to be limited too. If not...
not.