Re: Linux TOP

On Wed, 21 Oct 2009, Waldomiro wrote:

> top - 16:16:30 up 42 days, 13:23,  4 users,  load average: 3.13, 3.52, 3.36
> Cpu(s):  1.4%us,  1.1%sy,  0.0%ni, 84.4%id, 12.9%wa,  0.0%hi,  0.2%si,  0.0%st
> Mem:  16432240k total, 16344596k used,    87644k free,    27548k buffers
> Swap: 10241428k total,  3680860k used,  6560568k free,  6230376k cached
>
> I'm afraid of two things, one is the "load average", I think 3 is too much

You're at 12.9% waiting for I/O and 84.4% idle. That means your average
load consists of three processes who are stuck waiting for I/O at any
given time. The I/O is what you should be worried about, not the load
average.

> another is the "swap", almost 4GB of swap, I think that is too much
> swap.

It does look like your server is using much more RAM than it actually has,
which is the likely reason for all the disk I/O. If you sort the top
output by memory, you might see why that is.

The information provided by top on Linux isn't very good though; take a
look at /proc/meminfo for more details. Rather than rely on top's math,
instead I usually capture the output from:

ps -e -o pid,rss,vsz,size,user,cmd

And add things up myself instead, taking into account the shared bits each
of the PostgreSQL processes includes.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD
>From pgsql-general-owner(at)postgresql(dot)org Wed Oct 21 19:08:59 2009
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Date: Wed, 21 Oct 2009 16:08:47 -0600
Message-ID: <dcc563d10910211508v73e2f530sad05438b84dbd7cb(at)mail(dot)gmail(dot)com>
Subject: Re: Linux TOP
From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: Greg Smith <gsmith(at)gregsmith(dot)com>
Cc: Waldomiro <waldomiro(at)shx(dot)com(dot)br>, pgsql-general(at)postgresql(dot)org
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On Wed, Oct 21, 2009 at 4:01 PM, Greg Smith <gsmith(at)gregsmith(dot)com> wrote:
> On Wed, 21 Oct 2009, Waldomiro wrote:
>
>> top - 16:16:30 up 42 days, 13:23,=A0 4 users,=A0 load average: 3.13, 3.5=
2,
>> 3.36
>> Cpu(s):=A0 1.4%us,=A0 1.1%sy,=A0 0.0%ni, 84.4%id, 12.9%wa,=A0 0.0%hi,=A0=
0.2%si,
>> 0.0%st
>> Mem:=A0 16432240k total, 16344596k used,=A0=A0=A0 87644k free,=A0=A0=A0 =
27548k buffers
>> Swap: 10241428k total,=A0 3680860k used,=A0 6560568k free,=A0 6230376k c=
ached
>>
>> I'm afraid of two things, one is the "load average", I think 3 is too mu=
ch
>
> You're at 12.9% waiting for I/O and 84.4% idle. =A0That means your averag=
e
> load consists of three processes who are stuck waiting for I/O at any giv=
en
> time. =A0The I/O is what you should be worried about, not the load averag=
e.
>
>> another is the "swap", almost 4GB of swap, I think that is too much swap=
.
>
> It does look like your server is using much more RAM than it actually has=
,
> which is the likely reason for all the disk I/O. =A0If you sort the top o=
utput
> by memory, you might see why that is.

This is a common misunderstanding.

In this:

Mem: 16432240k total, 16344596k used, 87644k free, 27548k buffers
Swap: 10241428k total, 3680860k used, 6560568k free, 6230376k cached

The 6.2G cached is considered part of the 16G used

So it's not using more memory than it has. It's just the accounting
is inobvious.