Hi Michael,

Thanls for your response.

Michael Fuhr wrote:
> On Mon, Mar 06, 2006 at 04:29:49PM +0100, Joost Kraaijeveld wrote:
>> Below are some results of running pgbench, run on a machine that
>> is doing nothing else than running PostgreSQL woth pgbench. The
>> strange thing is that the results are *constantly alternating* hight
>> (750-850 transactions)and low (50-80 transactions), no matter how
>> many test I run. If I wait a long time (> 5 minutes) after running
>> the test, I always get a hight score, followed by a low one, followed
>> by a high one, low one etc.
>
> The default checkpoint_timeout is 300 seconds (5 minutes). Is it
> coincidence that the "long time" between fast results is about the
> same?
I have not measured the "long wait time". But I can run multiple test in 3 minutes: the fast test lasts 3 sec, the long one 40 secs (see below). During the tests there is not much activity on the partition where the logfiles are (other controller and disk than the database and swap)

postgres@panoramix:/usr/lib/postgresql/8.1/bin$ time ./pgbench -c 10 -t 150 test
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 100
number of clients: 10
number of transactions per client: 150
number of transactions actually processed: 1500/1500
tps = 531.067258 (including connections establishing)
tps = 541.694790 (excluding connections establishing)

real 0m2.892s
user 0m0.105s
sys 0m0.145s


postgres@panoramix:/usr/lib/postgresql/8.1/bin$ time ./pgbench -c 10 -t 150 test
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 100
number of clients: 10
number of transactions per client: 150
number of transactions actually processed: 1500/1500
tps = 37.064000 (including connections establishing)
tps = 37.114023 (excluding connections establishing)

real 0m40.531s
user 0m0.088s
sys 0m0.132s

>What's your setting?
Default.

> Are your test results more consistent
> if you execute CHECKPOINT between them?
Could you tell me how I could do that?



Groeten,

Joost Kraaijeveld
Askesis B.V.
Molukkenstraat 14
6524NB Nijmegen
tel: 024-3888063 / 06-51855277
fax: 024-3608416
e-mail: J.Kraaijeveld@Askesis.nl
web: www.askesis.nl

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On Mon, Mar 06, 2006 at 07:46:05PM +0100, Joost Kraaijeveld wrote:
> Michael Fuhr wrote:
> > What's your setting?
>
> Default.

Have you tweaked postgresql.conf at all? If so, what non-default
settings are you using?

> > Are your test results more consistent
> > if you execute CHECKPOINT between them?
>
> Could you tell me how I could do that?

Connect to the database as a superuser and execute a CHECKPOINT
statement.

http://www.postgresql.org/docs/8.1/i...heckpoint.html

From the command line you could do something like

psql -c checkpoint
pgbench -c 10 -t 150 test
psql -c checkpoint
pgbench -c 10 -t 150 test
psql -c checkpoint
pgbench -c 10 -t 150 test

--
Michael Fuhr

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