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Re: scaling multiple connections

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: mlw <markw(at)mohawksoft(dot)com>
Cc: Hackers List <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: scaling multiple connections
Date: 2001-04-26 15:53:56
Message-ID: 16497.988300436@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
mlw <markw(at)mohawksoft(dot)com> writes:
> I am getting a bit concerned about Postgres 7.1 performance with
> multiple connections. Postgres does not seem to scaling very
> well. Below there is a list of outputs from pgbench with different
> number of clients, you will see that postgres' performance in the
> benchmark drops with each new connection.  Shouldn't the tps stay
> fairly constant?

There was quite a long thread about this in pghackers back in Jan/Feb
(or so).  You might want to review it.  One thing I recall is that
you need a "scaling factor" well above 1 if you want meaningful results
--- at scale factor 1, all of the transactions want to update the same
row, so of course there's no parallelism and a lot of lock contention.

The default WAL tuning parameters (COMMIT_DELAY, WAL_SYNC_METHOD, and
friends) are probably not set optimally in 7.1.  We are hoping to hear
about some real-world performance results so that we can tweak them in
future releases.  I do not trust benchmarks as simplistic as pgbench for
doing that kind of tweaking, however.

			regards, tom lane

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