Subject: Re: Disk writes
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: carlosreimer <carlosreimer@terra.com.br>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
In-Reply-To: <J33AN6$0933748F3F76B26B2DA40DD16BAC2950@terra.com.br>
References: <J33AN6$0933748F3F76B26B2DA40DD16BAC2950@terra.com.br>
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Date: Fri, 28 Jul 2006 09:03:07 -0500

On Thu, 2006-07-27 at 20:25, carlosreimer wrote:
> Hi,
>  
> We've a fedora core 3 box with PostgreSQL 8.0.
>  
> There is some performance problems with the server and I discovered
> with vmstat tool that there is some process writing a lot of
> information in the disk subsystem.
>  
> I stopped the database and even so vmstat showed the same rates of
> disk writes.
>  
> I could I discover who is sending so many data to the disks?

Does top show any processes running?

On my FC4 laptop, the one that kept cranking up all the time was
prelink.  I don't really care if it takes an extra couple seconds for an
app to open each time, so I disabled that.

The other process I've seen do this, on older flavors of linux mostly,
is kswapd erroneously writing and reading the swap partition a lot. 
Seems to happen when the swap partition is smaller than physical memory,
and there's a lot of other I/O going on.  But I think that got fixed in
the 2.6 kernel tree.