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Re: Vacuum Problems

From: "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com>
To: "Rafael Domiciano" <rafael(dot)domiciano(at)gmail(dot)com>
Cc: "Matthew T(dot) O'Connor" <matthew(at)zeut(dot)net>, "Rafael Martinez" <r(dot)m(dot)guerrero(at)usit(dot)uio(dot)no>, "pgsql-admin(at)postgresql(dot)org" <pgsql-admin(at)postgresql(dot)org>
Subject: Re: Vacuum Problems
Date: 2008-12-08 17:28:16
Message-ID: dcc563d10812080928s90e324ch2978ffdd4e586225@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-admin
On Mon, Dec 8, 2008 at 10:17 AM, Rafael Domiciano
<rafael(dot)domiciano(at)gmail(dot)com> wrote:
> Here's the output. While the process was running my database get sometime
> without doing anything.
> You said that I probably get low numbers, but what numbers?

We're looking for MB/s and the bi/bo fields in bmstat (blocks in / blocks out)

> [root(at)postgres banco]# time dd if=/dev/zero of=/banco/testfile bs=1000000
> count=500
> 500+0 records in
> 500+0 records out
> 500000000 bytes (500 MB) copied, 85,4485 seconds, 5,9 MB/s
> real    1m25.451s
> user    0m0.003s
> sys     0m1.617s
> [root(at)postgres banco]# time dd of=/dev/null if=/banco/testfile
> 976562+1 records in
> 976562+1 records out
> 500000000 bytes (500 MB) copied, 47,5025 seconds, 10,5 MB/s
> real    0m47.543s
> user    0m0.457s
> sys     0m1.470s
> And the vmstat output:
>
> procs -----------memory---------- ---swap-- -----io---- --system--
> -----cpu------
>  r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id
> wa st
>  0  8 111760  56432  19812 1305692    0    0   744   832 2488  1518  5  3 46
> 46  0

Here, the bi/bo numbers are 768 in and 832 out.  That's k/second we're
looking at.

Lots of the same numbers cut out.

> procs -----------memory---------- ---swap-- -----io---- --system--
> -----cpu------
>  r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id
> wa st
>  0  6 111760  55452  18528 1296412    0    0    88 25040 1843  1436  2  3 34
> 61  0
>  1  7 111760  52352  18540 1296472    0    0    36 15220 1467   944  3  2 27
> 68  0
>  0  6 111760  54152  18552 1296568    0    0    88 42296 1609   822  1  2 38
> 59  0
>  1  8 111760  52412  18580 1296752    0    0   172 27052 1567   950  2  3 27
> 69  0
>  0  6 111724  53904  18632 1297008  320    0   580  1504 1902  2320  5  6 23
> 66  0
>  1  6 111724  54280  18660 1297200    4    0   200  1060 2014  1783  5  3 44
> 48  0
>  1  7 111676  51388  16340 1302348    8    0   156  1212 1684   848  2  2 53
> 42  0
>  1  6 111668  55040  14864 1301048    0    4   152 46328 1595  5108  1  5 40
> 54  0

Now we're showing that we can write to the disk at 25 to 42 Megs a
second, not too bad.  But it looks really bursty, like it can sustain
this throughput for only a few seconds.   Try writing a larger file
and run vmstat 10 or 60 as well and see what the average over a longer
time with a larger file is.  I get a feeling your machine has a hard
time sustaining throughput for some reason.

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