Re: Doubt in pgbench TPS number

Hello Tatsuo-san,

>> I think that the degree of parallelism to consider is nclients, not
>> nthreads: while connection time is accumulated in conn_time, other
>> clients are possibly doing their transactions, in parallel,
>
> I'm not sure about this. I think pgbench will not start transactions
> until all clients establish connections to PostgreSQL.

I think that is true if "!is_connect", all client connections are
performed at the beginning of threadRun, but under -C each client has its
own connect/deconnect integrated within doCustom, so it is done in
parallel to other clients having their transactions processed, hence the
issue with the formula.

> I found this while playing with pgpool-II. pgpool-II pre-forks child
> process, whose number is defined by "num_init_children"
> directive. What I observed was, pgbench starts connecting to pgpool-II
> until "-c" connections are established. So, if "-c" is larger than
> "num_init_children", no transaction starts.

Yep, unless -C, I think, where some client may start nevertheless? Not
sure... Does not matter.

> I have tested your patch. It seems the tolerance is much better than
> before with your patch.

Yep.

> I'm going to commit your patch if there's no objection.

This seems fine with me.

The formula change, and just this one, should probably be backported
somehow, as this is a bug, wherever pgbench resides in older versions. It
is just 's/nthreads/nclients/' in the printResult formula for computing
tps_exclude.

--
Fabien.