On Dec 13, 2007 6:06 AM, Ow Mun Heng <Ow.Mun.Heng@wdc.com> wrote:
> I'm using centos 5 as the OS so, there's no fancy dtrace to look at
> which processes is causing my disks to thrash.
>
> I have 4 disks in the box. (all ide, 7200rpm)
>
> 1 OS disk [hda]
> 2 raided (1) disks [hdb/hdc]
> 1 pg_xlog disk (and also used as an alternate tablespace for [hdd]
> temp/in-transit files via select, insert into tmp table. delete from tmp
> table, insert into footable select * from tmp table)
>
> Problem now I see from both atop and iostat, the Device: (iostat -dx 10)
>
> rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
> hda 98.60 14.69 121.98 15.08 1775.02 2908.29 34.17 47.53 551.67 7.29 99.95
> hdb 0.70 4.20 16.48 2.30 304.50 51.95 18.98 0.21 10.94 8.45 15.86
> hdc 0.00 3.40 12.49 2.00 223.78 43.16 18.43 0.07 5.04 4.42 6.40
> hdd 0.00 56.94 0.50 3.70 53.55 485.91 128.57 0.02 5.48 3.95 1.66
> md0 0.00 0.00 29.57 11.89 526.67 95.10 15.00 0.00 0.00 0.00 0.00
>
> the number of writes and reads on hda is much greater than expected and I'm not sure who/what is causing it.
there are a few things that I can think of that can can cause postgres
to cause i/o on a drive other than the data drive:
* logging (eliminate this by moving logs temporarily)
* swapping (swap is high and changing, other ways)
* dumps, copy statement (check cron)
* procedures, especially the external ones (perl, etc) that write to disk
my seat-of-the-pants guess is that you are looking at swap.
of course, a runaway program other than postgres can be the cause
merlin