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Re: Slow Vacuum was: vacuum output question

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On PostgreSQL 8.1, while a long vacuum is running, the output of
vmstat 10 looks like this (sorry, can't format this very will in this
e-mail client):

r  b   swpd   free     buff     cache     si   so    bi       bo
in   cs      us  sy id wa st
5  2    112  53732   4388 1163404    0    0 13524  1322  941 75053 45
55  0  0  0
3  2    112  51596   2336 1160032    0    0 20731   732  999 196116 35
58  0  7  0
3  2    112  53784   2448 1155388    0    0  5729  1680  716 114442 46
52  0  2  0
7  1    112  52088   2568 1156796    0    0   205  1919  546 28929 56
44  0  0  0
3  2    112  51772   2652 1157028    0    0   162  2010  534 2845 56 44  0  0  0
3  2    112  52296   2736 1156332    0    0   174  1910  517 2648 53 47  0  0  0
2  2    112  52736   2832 1155388    0    0   173  1960  521 2698 57 43  0  0  0
6  1    112  51172   2908 1157400    0    0   173  1825  511 2621 52 48  0  0  0
2  1    112  52156   2984 1155876    0    0   152  1766  495 2669 53 47  0  0  0
5  2    112  53828   3064 1154028    0    0   124  1762  498 2673 54 46  0  0  0
5  0    112  53396   3140 1154684    0    0   122  1803  532 2871 52 48  0  0  0
6  1    112  52004   3240 1155892    0    0   150  2004  522 3712 56 44  0  0  0
5  2    112  53100   3348 1152364    0    0   128  2142  543 2711 54 38  0  8  0
1  2    112  56704   3428 1148132    0    0   102  2229  560 2925 56 44  0  0  0
2  1    112  54876   3500 1150080    0    0    91  2129  598 3068 65 35  0  0  0
3  1    112  53196   3588 1152164    0    0    90  2091  542 2803 57 43  0  0  0
8  2    112  53528   3664 1151868    0    0   106  2180  553 2947 55 39  0  6  0

Vacuum hasn't stopped yet at this point - its been running for many minutes.


On PostgreSQL 8.3, we had this:

 r   b   swpd   free     buff        cache     si   so    bi     bo
 in   cs    us  sy id wa st
 6  0   9604  51932  14276 1138996    0    0     3  1808  523 5115 45
9 42  4  0
 2  0   9580  53284  14124 1138092   10    0   564  2561  585 5126 53
10 19 18  0
 7  0   9564  53412  14144 1137696    0    0     0  1682  497 4985 42
9 48  2  0
 3  0   9532  53320  13880 1137940    6    0    37  1757  538 4979 48  8 41  3

More random data:

On an overnight test of PostgreSQL 8.3 on Fedora Core 6, with
auto-vacuum on (using all default settings) the amount of time that it
takes to run a manual vacuum on a constant sized database (only row
updates, or deletes followed by a replacement add) has doubled from 2
seconds to 4 seconds.  A reindex brings the time back down to 2
seconds.

Dan

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