Date: Wed, 8 Sep 2010 15:00:11 -0700
From: David Kerr <dmk@mr-paradox.net>
To: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: Greg Smith <greg@2ndquadrant.com>, pgsql-performance@postgresql.org,
	Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: pgbench could not send data to client: Broken pipe
Message-ID: <20100908220011.GA59539@mr-paradox.net>
References: <20100908174629.GD40339@mr-paradox.net>
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	<20100908195654.GB49941@mr-paradox.net>
	<9771.1283978128@sss.pgh.pa.us>
	<20100908204443.GG49941@mr-paradox.net>
	<4C87B22802000025000353B7@gw.wicourts.gov>
	<20100908212056.GI49941@mr-paradox.net>
	<4C87BF0502000025000353BE@gw.wicourts.gov>
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On Wed, Sep 08, 2010 at 04:51:17PM -0500, Kevin Grittner wrote:
- David Kerr <dmk@mr-paradox.net> wrote:
-  
- > Hmm, i'm not following you. I've got 48 cores. that means my
- > sweet-spot active connections would be 96.
-  
- Plus your effective spindle count.  That can be hard to calculate,
- but you could start by just counting spindles on your drive array.

We've got this weird LPAR thing at our hosting center. it's tough
for me to do.

- > Now if i were to connection pool that out to 15 people per
- > connection,
-  
- Where did you get that number?  We routinely route hundreds of
- requests per second (many of them with 10 or 20 joins) from five or
- ten thousand connected users through a pool of 30 connections.  It
- started out bigger, we kept shrinking it until we hit our sweet
- spot.  The reason we started bigger is we've got 40 spindles to go
- with the 16 cores, but the active portion of the database is cached,
- which reduces our effective spindle count to zero.

That's encouraging. I don't remember where I got the number from,
but my pooler will be Geronimo, so i think it came in that context.

- > that's 1440 users "total" able to use my app at one time. (with
- > only 96 actually doing anything). not really great for a web-based
- > app that will have millions of users accessing it when we're fully
- > ramped up.
-  
- Once you have enough active connections to saturate the resources,
- adding more connections just adds contention for resources and
- context switching cost -- it does nothing to help you service more
- concurrent users.  The key is, as I mentioned before, to have the
- pooler queue requests above the limit and promptly get them running
- as slots are freed.

Right, I understand that. My assertian/hope is that the saturation point
on this machine should be higher than most.

Dave