7.3.4 on Linux: UPDATE .. foo=foo+1 degrades massivly over time

Hello,

postgresql 7.3.4 on Debian or the redhat packaged 7.3.4-8 on RHEL AS3 -
same issue, so I somewhat cut out RH is playing things on me.
Tested on two different PCs, too (say, one debian, one RHEL).

While running
UPDATE banner SET counterhalf=counterhalf+1 WHERE BannerID=50
several thousand times, the return times degrade (somewhat linear).
The relation banner has currently *seven* rows and thus it doesnt matter
(and i checked :>) if counterhalf is indexed, or not.

A following VACCUM brings back return times to 'start' - but I cannot
run VACUUM any other minute (?). And it exactly vaccums as many tuples
as I updated.. sure thing:
INFO:  Removed 5000 tuples in 95 pages.
        CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  Pages 95: Changed 1, Empty 0; Tup 7: Vac 5000, Keep 0, UnUsed 3.
        Total CPU 0.01s/0.03u sec elapsed 0.04 sec.

What I cant explain is the query statistics output:
'In the beginning':
DEBUG:  StartTransactionCommand
LOG:  query: UPDATE banner SET counterhalf=counterhalf+1 WHERE BannerID=50
DEBUG:  ProcessQuery
DEBUG:  CommitTransactionCommand
LOG:  QUERY STATISTICS
! system usage stats:
!       0.001110 elapsed 0.000000 user 0.000000 system sec
!       [0.940000 user 0.080000 sys total]
!       0/0 [0/0] filesystem blocks in/out
!       0/0 [437/192] page faults/reclaims, 0 [0] swaps
!       0 [0] signals rcvd, 0/0 [0/0] messages rcvd/sent
!       0/0 [0/0] voluntary/involuntary context switches
! buffer usage stats:
!       Shared blocks:          0 read,          0 written, buffer hit rate = 100.00
%
!       Local  blocks:          0 read,          0 written, buffer hit rate = 0.00%
!       Direct blocks:          0 read,          0 written

After 5000 updates:
DEBUG:  StartTransactionCommand
LOG:  query: UPDATE banner SET counterhalf=counterhalf+1 WHERE BannerID=50
DEBUG:  ProcessQuery
DEBUG:  CommitTransactionCommand
LOG:  QUERY STATISTICS
! system usage stats:
!       0.002503 elapsed 0.000000 user 0.000000 system sec
!       [8.400000 user 0.740000 sys total]
!       0/0 [0/0] filesystem blocks in/out
!       0/0 [711/192] page faults/reclaims, 0 [0] swaps
!       0 [0] signals rcvd, 0/0 [0/0] messages rcvd/sent
!       0/0 [0/0] voluntary/involuntary context switches
! buffer usage stats:
!       Shared blocks:          0 read,          0 written, buffer hit rate = 100.00%
!       Local  blocks:          0 read,          0 written, buffer hit rate = 0.00%
!       Direct blocks:          0 read,          0 written

I checked all 5000 entries, and (obviously?) never touches the filesystem.
Where I stumble is that it keeps down with 'elapsed' time, but the user/sys
times grow linear (which is corresponding to wallclock).

The effect is the same (only in other ranges) with a default or "tuned"
postgresql.conf and either on debian or the RHEL machine.

I dont know where to go now. I was reading the whole changelog/history from
7.3.4 up to 7.4.2 and only found 'auto vacuum' - which might be a deal, yet
it needs permanent statistics (really?) and thus would eat response time
on the other hand then.

And for the very record I tried this on a mysql4.0.18 where the return time
is in general faster (dont care), but it also doesnt degrade over even 50.000
updates (do care here >:).

Next thing is profiling postgres to see, where it loses the time, but
maybe someone already can point me at something.

Any pointer is appreciated.. link to an archived mail (search on archives is
quite slow, too? :) ), pointer to some "hidden" doc I might have missed or
a different SQL possibility to count banner-views in pgsql.

Thanks for any consideration,
--
Philipp Buehler, aka fips | <double-p>

cvs -d /dev/myself commit -m "it's my life" dont/you/forget