Re: Ever Increasing IOWAIT

Ralph Mason wrote:
> We have a database running on a 4 processor machine. As time goes by
> the IO gets worse and worse peeking at about 200% as the machine loads up.
>
> The weird thing is that if we restart postgres it’s fine for hours but
> over time it goes bad again.
>
> (CPU usage graph here HYPERLINK
> "http://www.flickr.com/photos/8347741(at)N02/502596262/"http://www.flickr
> .com/p hotos/8347741(at)N02/502596262/ ) You can clearly see where the
> restart happens in the IO area
>I'm assuming here we're talking about that big block of iowait at about
>4-6am?

Actually no - that is a vacuum of the whole database to double check It's
not a vacuuming problem (I am sure it's not). The restart is at at 22:00
where you see the io drop to nothing, the database is still doing the same
work.

>>I take it vmstat/iostat show a corresponding increase in disk activity
>>at that time.

I didn't know you could have IO/wait without disk activity - I will check
that out.

>>The question is - what?
>>Does the number of PG processes increase at that time? If that's not
>>intentional then you might need to see what your applications are up to.

No the number of connections is stable and the jobs they do stays the same,
just this deteriorating of i/o wait over time.

>>Do you have a vacuum/backup scheduled for that time? Do you have some
>>other process doing a lot of file I/O at that time?

> This is Postgres 8.1.4 64bit.

>You'll want to upgrade to the latest patch release - you're missing 5
>lots of bug-fixes there.

Thanks - will try that.

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