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Message-ID: <fd145f7d0807072039k63b2deffp6aa709f2155385db@mail.gmail.com>
Date: Mon, 7 Jul 2008 20:39:28 -0700
From: "Jeffrey Baker" <jwbaker@gmail.com>
To: "Greg Smith" <gsmith@gregsmith.com>
Subject: Re: Practical upper limits of pgbench read/write tps with 8.3
Cc: "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
In-Reply-To: <Pine.GSO.4.64.0807071803150.13336@westnet.com>
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References: <fd145f7d0807071405t1bdf4be0j8583fc9965a7719e@mail.gmail.com>
	<Pine.GSO.4.64.0807071803150.13336@westnet.com>

On Mon, Jul 7, 2008 at 3:22 PM, Greg Smith <gsmith@gregsmith.com> wrote:
> On Mon, 7 Jul 2008, Jeffrey Baker wrote:
>
>> On the single 2.2GHz Athlon, the maximum tps seems to be 1450...what's the
>> bottleneck?  Is PG lock-bound?
>
> It can become lock-bound if you don't make the database scale significantly
> larger than the number of clients, but that's probably not your problem.
>  The pgbench client driver program itself is pretty CPU intensive and can
> suffer badly from kernel issues.  I am unsurprised you can only hit 1450
> with a single CPU.  On systems with multiple CPUs where the single CPU
> running the pgbench client is much faster than your 2.2GHz Athlon, you'd
> probably be able to get a few thousand TPS, but eventually the context
> switching of the client itself can become a bottleneck.

On a 2GHz Core 2 Duo the best tps achieved is 2300, with -c 8.
pgbench itself gets around 10% of the CPU (user + sys for pgbench is
7s of 35s wall clock time, or 70 CPU-seconds, thus 10%).

I suppose you could still blame it on ctxsw between pgbench and pg
itself, but the results are not better with pgbench on another machine
cross-connected with gigabit ethernet.

-jwb