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* RES: Bad iostat numbers
@ 2006-12-01 14:29 Carlos H. Reimer <carlos.reimer@opendb.com.br>
2006-12-01 15:32 ` Re: RES: Bad iostat numbers David Boreham <david_list@boreham.org>
0 siblings, 1 reply; 3+ messages in thread
From: Carlos H. Reimer @ 2006-12-01 14:29 UTC (permalink / raw)
To: david_list@boreham.org; +Cc: pgsql-performance
Hi,
I´ve taken a look in the /var/log/messages and found some temperature
messages about the disk drives:
Nov 30 11:08:07 totall smartd[1620]: Device: /dev/sda, Temperature changed 2
Celsius to 51 Celsius since last report
Can this temperature influence in the performance?
Reimer
> -----Mensagem original-----
> De: David Boreham [mailto:david_list@boreham.org]
> Enviada em: sexta-feira, 1 de dezembro de 2006 00:25
> Para: carlos.reimer@opendb.com.br
> Cc: pgsql-performance@postgresql.org
> Assunto: Re: [PERFORM] Bad iostat numbers
>
>
> Carlos H. Reimer wrote:
>
> >
> >
> > avg-cpu: %user %nice %system %iowait %idle
> >
> > 50.40 0.00 0.50 1.10 48.00
> >
> >
> >
> > Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s
> > avgrq-sz avgqu-sz await svctm %util
> >
> > sda 0.00 7.80 0.40 6.40 41.60 113.60 20.80
> > 56.80 22.82 570697.50 10.59 147.06 100.00
> >
> > sdb 0.20 7.80 0.60 6.40 40.00 113.60 20.00
> > 56.80 21.94 570697.50 9.83 142.86 100.00
> >
> > md1 0.00 0.00 1.20 13.40 81.60 107.20 40.80
> > 53.60 12.93 0.00 0.00 0.00 0.00
> >
> > md0 0.00 0.00 0.00 0.00 0.00 0.00 0.00
> > 0.00 0.00 0.00 0.00 0.00 0.00
> >
> >
> >
> > Are they not saturated?
> >
> >
> >
> > What kind of parameters should I pay attention when comparing SCSI
> > controllers and disks? I would like to discover how much cache is
> > present in the controller, how can I find this value from Linux?
> >
> >
> These number look a bit strange. I am wondering if there is a hardware
> problem on one of the drives
> or on the controller. Check in syslog for messages about disk timeouts
> etc. 100% util but 6 writes/s
> is just wrong (unless the drive is a 1980's vintage floppy).
>
>
>
>
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: RES: Bad iostat numbers
2006-12-01 14:29 RES: Bad iostat numbers Carlos H. Reimer <carlos.reimer@opendb.com.br>
@ 2006-12-01 15:32 ` David Boreham <david_list@boreham.org>
0 siblings, 0 replies; 3+ messages in thread
From: David Boreham @ 2006-12-01 15:32 UTC (permalink / raw)
To: carlos.reimer@opendb.com.br; +Cc: pgsql-performance
Carlos H. Reimer wrote:
>I´ve taken a look in the /var/log/messages and found some temperature
>messages about the disk drives:
>
>Nov 30 11:08:07 totall smartd[1620]: Device: /dev/sda, Temperature changed 2
>Celsius to 51 Celsius since last report
>
>Can this temperature influence in the performance?
>
>
it can influence 'working-ness' which I guess in turn affects performance ;)
But I'm not sure if 50C is too high for a disk drive, it might be ok.
If you are able to, I'd say just replace the drives and see if that
improves things.
^ permalink raw reply [nested|flat] 3+ messages in thread
* RES: Bad iostat numbers
@ 2006-12-01 14:47 Carlos H. Reimer <carlos.reimer@opendb.com.br>
0 siblings, 0 replies; 3+ messages in thread
From: Carlos H. Reimer @ 2006-12-01 14:47 UTC (permalink / raw)
To: Mark Kirkwood <markir@paradise.net.nz>; +Cc: pgsql-performance
Hi,
If you look the iostat data it shows that the system is doing much more
writes than reads. It is strange, because if you look in the pg_stat tables
we see a complete different scenario. Much more reads than writes. I was
monitoring the presence of temporary files in the data directory what could
denote big sorts, but nothing there too.
But I think it is explained because of the high number of indexes present in
those tables. One write in the base table, many others in the indexes.
Well, about the server behaviour, it has not changed suddenly but the
performance is becoming worse day by day.
Reimer
> -----Mensagem original-----
> De: Mark Kirkwood [mailto:markir@paradise.net.nz]
> Enviada em: quinta-feira, 30 de novembro de 2006 23:47
> Para: carlos.reimer@opendb.com.br
> Cc: pgsql-performance@postgresql.org
> Assunto: Re: [PERFORM] Bad iostat numbers
>
>
> Carlos H. Reimer wrote:
> > While collecting performance data I discovered very bad numbers in the
> > I/O subsystem and I would like to know if I´m thinking correctly.
> >
> > Here is a typical iostat -x:
> >
> >
> > avg-cpu: %user %nice %system %iowait %idle
> >
> > 50.40 0.00 0.50 1.10 48.00
> >
> >
> >
> > Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s
> > avgrq-sz avgqu-sz await svctm %util
> >
> > sda 0.00 7.80 0.40 6.40 41.60 113.60 20.80
> > 56.80 22.82 570697.50 10.59 147.06 100.00
> >
> > sdb 0.20 7.80 0.60 6.40 40.00 113.60 20.00
> > 56.80 21.94 570697.50 9.83 142.86 100.00
> >
> > md1 0.00 0.00 1.20 13.40 81.60 107.20 40.80
> > 53.60 12.93 0.00 0.00 0.00 0.00
> >
> > md0 0.00 0.00 0.00 0.00 0.00 0.00 0.00
> > 0.00 0.00 0.00 0.00 0.00 0.00
> >
> >
> >
> > Are they not saturated?
> >
>
> They look it (if I'm reading your typical numbers correctly) - %util 100
> and svctime in the region of 100 ms!
>
> On the face of it, looks like you need something better than a RAID1
> setup - probably RAID10 (RAID5 is probably no good as you are writing
> more than you are reading it seems). However read on...
>
> If this is a sudden change in system behavior, then it is probably worth
> trying to figure out what is causing it (i.e which queries) - for
> instance it might be that you have some new queries that are doing disk
> based sorts (this would mean you really need more memory rather than
> better disk...)
>
> Cheers
>
> Mark
>
>
>
>
>
^ permalink raw reply [nested|flat] 3+ messages in thread
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2006-12-01 14:29 RES: Bad iostat numbers Carlos H. Reimer <carlos.reimer@opendb.com.br>
2006-12-01 15:32 ` David Boreham <david_list@boreham.org>
2006-12-01 14:47 RES: Bad iostat numbers Carlos H. Reimer <carlos.reimer@opendb.com.br>
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