From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
---|---|
To: | Praveen Kumar N <praveen_n(at)students(dot)iiit(dot)net> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: system cache and buffer cache |
Date: | 2006-09-20 03:33:00 |
Message-ID: | 20060920033300.GG31466@alvh.no-ip.org |
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Lists: | pgsql-hackers |
Praveen Kumar N wrote:
> Hi,
> can anybody explain me what is the difference between system cache
> and buffer cache?
>
> I found that keywords in PostgreSql FAQ
> http://www.postgresql.org/docs/faqs.FAQ_DEV.html#item2.1
Another important cache is the "relation cache", relcache for short,
which is also stored in local memory.
One important point about these (relcache, syscache, catcaches = catalog
caches) is that they are invalidated using the "sinval" system, which
passes messages from one backend to all others via a queue in shared
memory. The buffer cache needs no such thing, precisely because it
lives in shared memory. But it needs to be protected by locks.
--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
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