Tom Lane wrote:
> It is notoriously hard to get reproducible results from pgbench.
> However...
>
>
>>- I'm running pgbench with 35 clients and 50 transactions/client
>
>
> (1) what scale factor did you use to size the database? One of the
> gotchas is that you need to use a scale factor at least as large as the
I forgot to mention that - I read the pgbench README, and the scale
factor was set to 40.
> (2) 50 xacts/client is too small to get anything reproducible; you'll
> mostly be measuring startup transients. I usually use 1000 xacts/client.
I was using 100 and 50, hoping that the larger value will help
reproducability and the smaller just what you said - to measure startup
time. What I also forgot to mention was that the numbers I was talking
about were got by using '-C' pgbench switch. Without it the results wary
from about 60 and 145 (same 'alternating' effects, etc).
Thanks, I will try 1000 transactions!
There's another thing I'm puzzled about: I deliberately used -C switch
in intention to measure connection time, but with it, the numbers
displayed by pgbench for 'tps with' and 'tps without connection time'
are same to the 6th decimal place. Without -C, both numbers are more
then doubled and are different by about 2-3 tps. (I was expecting that
with -C the 'tps with c.t.' would be much lower than 'tps without c.t.').
(the README is here:
http://developer.postgresql.org/cvsweb.cgi/pgsql-server/contrib/pgbench/README.pgbench)
