Re: Doubt in pgbench TPS number - Mailing list pgsql-hackers

> 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 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.

> even if it
> is in the same thread, so it is not "stopped time" for all clients. It
> starts to matter with "-j 1 -c 30" and slow transactions, the
> cumulated conn_time in each thread may be arbitrary close to the whole
> time if there are many clients.
> 
> Now, I do not think that this tps computation makes that much
> sense. If you want to know the tps without reconnect, run without
> reconnecting... It is clear that I do not get this figure when running
> without -C, so maybe
> the tps with/without reconnection should be dropped?
> 
> Anyway, here is a patch, which:
>  - fixes the "exclude" computation (s/nthreads/nclients/)
>  - fixes the count total for skipped (s/threads/thread/)
>  - removes a useless parameter to doCustom
>    (the conn_time is available through the thread parameter).

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

With the patch:
./pgbench -C -n -p 11002 -c 10 -T 30 -f test.sql  test
transaction type: Custom query
scaling factor: 1
query mode: simple
number of clients: 10
number of threads: 1
duration: 30 s
number of transactions actually processed: 2887
latency average: 103.914 ms
tps = 95.896850 (including connections establishing)
tps = 98.101662 (excluding connections establishing)

Without the patch:
./pgbench -C -n -p 11002 -c 10 -T 30 -f test.sql  test
transaction type: Custom query
scaling factor: 1
query mode: simple
number of clients: 10
number of threads: 1
duration: 30 s
number of transactions actually processed: 2887
latency average: 103.914 ms
tps = 95.919415 (including connections establishing)
tps = 124.732475 (excluding connections establishing)

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

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp