Subject: Re: concurrent connections is worse than serialization?
From: Wei Weng <wweng@kencast.com>
To: Richard Huxton <dev@archonet.com>
Cc: pgsql-sql@postgresql.org
In-Reply-To: <200208141549.57646.dev@archonet.com>
References: <1029271170.16828.7.camel@Monet>
	<200208141018.38875.dev@archonet.com> <1029334827.21470.2.camel@Monet>
	<200208141549.57646.dev@archonet.com>
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Date: 14 Aug 2002 11:29:26 -0400
Message-Id: <1029338971.21470.9.camel@Monet>
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On Wed, 2002-08-14 at 10:49, Richard Huxton wrote:
> On Wednesday 14 Aug 2002 3:20 pm, Wei Weng wrote:
> > On Wed, 2002-08-14 at 05:18, Richard Huxton wrote:
> > > On Tuesday 13 Aug 2002 9:39 pm, Wei Weng wrote:
> 
> [30 connections is much slower than 1 connection 30 times]

Yeah, but the problem is, say I have 20 users using select on the
database at the same time, and each select takes 10 seconds to finish. I
really can't queue them up (or the last user will reall have to wait for
a long time), can I?

> 
> > > What was the limiting factor during the test? Was the CPU maxed, memory,
> > > disk I/O?
> >
> > No, none of the above was maxed. CPU usage that I paid attention to was
> > at most a 48%.
> 
> Something must be the limiting factor. One of
>  - CPU
>  - Memory
>  - Disk I/O
>  - Database (configuration, or design)
>  - Application
> 
> If it's not CPU, is the system going into swap or are you seeing a lot of disk 
> activity?
I did hear a lot of disk noise when I ran the test. How do I tell if the
"system is going into swap"?

Is there any system settings I can/should change to make this a little
faster? 

> 
> > > I assume you've ruled the application end of things out.
> >
> > What does this mean?
> 
> I mean if you don't actually run the queries, then 30 separate processes is 
> fine?
> 
> If you can provide us with an EXPLAIN of the query and the relevant schema 
> definitions, we can rule out database design.
> 

This is actually really simple.

A table like 

--------------------
| foo              | 
--------------------
|ID    VARCHAR(40) | --> primary key
|Name  VARCHAR(100)|
--------------------

And I did an INSERT INTO foo ('some-unique-guid-here', 'Test Name');

So I don't think it is any matter of the database. 

Thanks

-- 
Wei Weng
Network Software Engineer
KenCast Inc.