From: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
---|---|
To: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Piggybacking vacuum I/O |
Date: | 2007-01-24 08:28:35 |
Message-ID: | 45B718B3.5070901@enterprisedb.com |
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Lists: | pgsql-hackers |
Pavan Deolasee wrote:
> I have just counted the number of read/write calls on the CLOG blocks. As
> you can
> see the total number of CLOG reads jumped from 545323 to 1181851 i.e.
> 1181851 - 545323 = 636528 CLOG block reads for 1554697 pages of stock
> table.
Hmm. So there is some activity there. Could you modify the patch to
count how many of those reads came from OS cache? I'm thinking of doing
a gettimeofday() call before and after read, and counting how many
calls finished in less than say < 1 ms. Also, summing up the total time
spent in reads would be interesting.
Or, would it be possible to put the clog to a different drive, and use
iostat to get the numbers?
> This figure is only indicative since it also includes the CLOG block reads
> which would
> have happened as part of other backend operations (VACUUM took almost 55
> minutes to
> complete). Still in the first 210 minutes of the run, the total reads were
> only 545323. So
> most of the 636528 reads in the next 55 minutes can be attributed to
> VACUUM.
Actually, clog reads during normal activity is even worse.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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