Re: Vacuum Problem

From: plu tard <plutard12(at)hotmail(dot)com>
To: <pgsql-novice(at)postgresql(dot)org>
Subject: Re: Vacuum Problem
Date: 2007-12-12 09:33:33
Message-ID: BAY108-W81140191E5850D3A4571DA6650@phx.gbl
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I seem to be having a similar problem. I'm trying to run a vacuum full on one
of my development machines and it seems really slow.

Take a look at this 'vmstat 1' output. It seems to be pegged in iowait:

r b swpd free buff cache si so bi bo in cs us sy id wa
1 11 34664 55388 6652 1604836 0 0 0 0 1247 3202 1 4 0 95
0 11 34664 55760 6652 1604836 0 0 0 0 1182 3165 1 4 0 95
0 11 34664 56256 6652 1604836 0 0 0 0 1227 3296 0 6 0 94
0 12 34664 56752 6652 1604836 0 0 0 0 1367 3814 1 4 0 95
0 12 34664 57372 6652 1604836 0 0 0 0 1174 3173 0 3 0 97
0 12 34664 57868 6652 1604836 0 0 0 0 1229 3169 1 4 0 95
0 12 34664 58240 6652 1604836 0 0 0 0 1282 3469 0 5 0 95
0 12 34664 58736 6652 1604836 0 0 0 0 1007 2428 1 4 0 95
0 12 34664 59232 6652 1604836 0 0 0 0 1246 3205 1 6 0 93
0 12 34664 59728 6652 1604836 0 0 0 0 1072 2895 1 3 0 96
0 12 34664 60100 6652 1604836 0 0 0 0 1182 3149 1 4 0 95
0 12 34664 60720 6652 1604836 0 0 0 0 1232 3352 0 8 0 92
0 12 34664 61092 6652 1604836 0 0 0 0 1166 2836 1 4 0 95
0 12 34664 61464 6652 1604836 0 0 0 0 1059 2696 0 3 0 97
6 12 34664 61960 6652 1604836 0 0 0 0 1066 2471 1 4 0 95
0 12 34664 62580 6652 1604836 0 0 0 0 1309 3624 1 6 0 93
0 12 34664 62952 6652 1604836 0 0 0 0 1121 2885 0 4 0 96
0 12 34664 63324 6652 1604836 0 0 0 0 925 1999 1 5 0 94
0 12 34664 63944 6652 1604836 0 0 0 0 1102 2938 1 2 0 97
0 12 34664 64440 6652 1604836 0 0 0 32 1016 2609 1 1 0 98
0 12 34664 64796 6652 1604836 0 0 0 0 1020 2684 3 6 0 91
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
7 12 34664 65244 6652 1604836 0 0 0 0 1094 3137 10 4 0 86
0 12 34664 65740 6652 1604836 0 0 0 1144 1135 2932 2 5 0 93
3 12 34664 64872 6652 1604836 0 0 0 4800 1029 3182 33 9 0 58
0 9 34664 65740 6652 1604836 0 0 0 6932 814 1931 5 5 0 90
4 5 34664 65120 6664 1606056 0 0 8 3184 809 813 35 14 0 51
0 6 34664 45344 6684 1606232 0 0 152 164320 1216 612 19 17 0 64
1 12 34664 44912 6688 1607888 0 0 44 0 690 899 31 15 0 54
0 13 34664 44264 6696 1608220 0 0 68 0 983 1508 3 6 0 91
0 13 34664 43832 6696 1608532 0 0 72 0 1052 1415 6 5 0 89

Is that normal? Does it look like a hardware misconfiguration of some sort?

Running Pg 8.2.5 on Ubuntu 7.04 with 2GB ram.
I have two IDE disks running software RAID 1.

postgresql.conf is hasn't been changed much except I increased
effective_cache_size to 1G. I also tried raising maintenance_work_mem
based on a previous message in this thread, but it didn't seem to make
any improvement.

/sbin/hdparm /dev/hda:
multcount = 16 (on)
IO_support = 1 (32-bit)
unmaskirq = 1 (on)
using_dma = 1 (on)
keepsettings = 0 (off)
readonly = 0 (off)
readahead = 256 (on)
geometry = 24792/255/63, sectors = 398297088, start = 0

I have each disk on a separate IDE channel, each configured as master.
One cable has a DVD on it too set as slave.

I have a similar machine, also with two disk RAID 1, and it seems to run
vacuum full much faster. It's on CentOS 4 with Pg 8.2.4. Same config
except it's using effective_cache_size of 2GB with 4GB total ram.

Any ideas for what to investigate?

Thanks.

D

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