Re: Vacuum Problems

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.