| From: | Greg Smith <greg(at)2ndquadrant(dot)com> |
|---|---|
| To: | Cédric Villemain <cedric(dot)villemain(dot)debian(at)gmail(dot)com> |
| Cc: | Richard Neill <rn214(at)cam(dot)ac(dot)uk>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Limited Shared Buffer Problem |
| Date: | 2010-01-29 22:19:41 |
| Message-ID: | 4B635EFD.7000403@2ndquadrant.com |
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| Lists: | pgsql-performance |
Cédric Villemain wrote:
> AFAIK effective_cache_size is estimation of OS Page Cache + Estimated
> Cache in shared_buffers.
>
Yes, the total value you set is used as is, and should include both
pieces of memory. The planner doesn't add the shared_buffers value to
the total first for you, as some people might guess it would.
The only thing effective_cache_size is used for is estimating how
expensive an index is likely to be to use, to make decisions like when
to do an index-based scan instead of just scanning the table itself.
--
Greg Smith 2ndQuadrant Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.com
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