Re: Confused about the buffer pool size

On 25/05/10 19:49, MMK wrote:
> Hello All:
> In the code (costsize.c), I see that effective_cache_size is set to DEFAULT_EFFECTIVE_CACHE_SIZE.
> This is defined as follows in cost.h
> #define DEFAULT_EFFECTIVE_CACHE_SIZE 16384
> But when I say
> show shared_buffers in psql I get,
> shared_buffers ---------------- 28MB
> In postgresql.conf file, the following lines appear
> shared_buffers = 28MB # min 128kB # (change requires restart)#temp_buffers = 8MB # min 800kB
>
> So I am assuming that the buffer pool size is 28MB = 28 * 128 = 3584 8K pages.
> So should effective_cache_size be set to 3584 rather than the 16384?

No. Please see the manual for what effective_cache_size means:

http://www.postgresql.org/docs/8.4/interactive/runtime-config-query.html#GUC-EFFECTIVE-CACHE-SIZE

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com