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Re: VACUUMing for 30 minutes

From: <ogjunk-pgjedan(at)yahoo(dot)com>
To: pgsql-admin(at)postgresql(dot)org
Subject: Re: VACUUMing for 30 minutes
Date: 2004-12-22 16:38:43
Message-ID: 20041222163844.93592.qmail@web12707.mail.yahoo.com (view raw or flat)
Thread:
Lists: pgsql-admin
Hello,

--- Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> <ogjunk-pgjedan(at)yahoo(dot)com> writes:
> > VACUUMing this DB takes about 30 minutes, and during that time the
> DB
> > is pretty unresponsive, although the PG process is not using a lot
> of
> > CPU (load ~ 1) nor memory (~20MB for the VACUUM process).
> 
> How big is the DB physically ("du $PGDATA" results)?

4.2 GB:

# du -h ~postgres/data
3.6M    /var/lib/pgsql/data/base/1
3.6M    /var/lib/pgsql/data/base/16975
4.0K    /var/lib/pgsql/data/base/16976/pgsql_tmp
4.1G    /var/lib/pgsql/data/base/16976
4.1G    /var/lib/pgsql/data/base
152K    /var/lib/pgsql/data/global
129M    /var/lib/pgsql/data/pg_xlog
1.1M    /var/lib/pgsql/data/pg_clog
4.2G    /var/lib/pgsql/data

> If you've been lax
> about vacuuming or not had your FSM parameters set high enough, there
> could be a whole lot of dead space for VACUUM to scan through.

I've been vacuuming every night, like a good DBwife.

> If so,
> VACUUM FULL or possibly CLUSTER would be the best way to re-compact
> the
> tables.  (VACUUM VERBOSE on your larger tables would be another way
> to
> investigate this.)

I will try VACUUM VERBOSE on the biggest (and most active) table
tonight and report the findings.

> The other possibility is that you have a seriously slow disk drive
> :-(

It looks like I have an ATA-6 drive with only 2MB cache, and the
following throughput:

# /sbin/hdparm -tT /dev/hda
                                                                       
                                                     
/dev/hda:
 Timing buffer-cache reads:   128 MB in  0.56 seconds =228.57 MB/sec
 Timing buffered disk reads:  64 MB in  1.18 seconds = 54.24 MB/sec

Not SCSI, not RAID, but not the slowest HDD on the continent.

Thanks,
Otis


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