| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Greg Smith <greg(at)2ndquadrant(dot)com> |
| Cc: | Ben Chobot <bench(at)silentmedia(dot)com>, pgsql-general <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: pg_buffercache's usage count |
| Date: | 2010-02-24 14:02:19 |
| Message-ID: | 20100224140219.GC3790@alvh.no-ip.org |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-general |
Greg Smith wrote:
> Ben Chobot wrote:
> >On Feb 23, 2010, at 3:06 PM, Ben Chobot wrote:
> >
> >>I'm looking at the usage count column of pg_buffercache's info, and I'm confused. Several buffers that supposed have LRU values of 5 belong to non-unique indices which supposedly have never been used. As I understand things, that shouldn't happen. Am I missing something?
> >
> >(And maybe more to the point, when does the LRU go down in value?)
>
> Usage counts only go up when a page is "pinned" because some backend
> requested that particular block for its work via a call to
> BufferAlloc with the file/block it needs.
BTW the only reason you don't see buffers having a larger "usage" is
that the counters are capped at that value.
--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
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