| From: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
|---|---|
| To: | Gokulakannan Somasundaram <gokul007(at)gmail(dot)com> |
| Cc: | Gregory Stark <stark(at)enterprisedb(dot)com>, Neil Conway <neilc(at)samurai(dot)com>, pgsql-hackers list <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: EXPLAIN ANALYZE printing logical and hardware I/O per-node |
| Date: | 2007-12-15 19:33:00 |
| Message-ID: | 47642BEC.1060205@enterprisedb.com |
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| Lists: | pgsql-hackers |
Gokulakannan Somasundaram wrote:
> I was going to say that I'm really only interested in physical I/O. Logical
>> I/O which is satisfied by the kernel cache is only marginally interesting
>> and
>> buffer fetches from Postgres's shared buffer is entirely uninteresting
>> from
>> the point of view of trying to figure out what is slowing down a query.
>
> Ok the Physical I/Os are already visible, if you enable log_statement_stats.
I think you missed the point. What log_statement_stats shows are not
physical I/Os, they're read() system calls. Unfortunately there's no
direct way to tell if a read() is satisfied from OS cache or not. Greg's
suggestion was about how to do that.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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