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List:       httpclient-users
Subject:    Re: What is the determining factor for Max Connections?
From:       Mike Boyers <mboyers () yahoo ! com>
Date:       2010-09-06 16:13:09
Message-ID: 261422.28114.qm () web110208 ! mail ! gq1 ! yahoo ! com
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I don't know of a concrete rule of thumb, but I'll share my thinking about how I've \
tuned my configuration.  I don't know if my way of thinking is common or not.

For me, the most important reason for having max-total-connections be something \
smaller than Integer.MAX_VALUE has to due more with the behavior when something is \
under duress as opposed to overall memory, cpu, etc.

If you have it set to "infinite" as you do currently, and one (or all) of the remote \
hosts your HttpClient is talking to becomes very slow in responding or unresponsive \
altogether, how many threads are you willing to have chewed up at any one given time \
by waiting for slow responses that may never come back with meaningful data?

I've worked with some folks who couldn't cache HttpClient responses (they were \
different every time), and who also were running at about 100 requests per second.  \
Their system would go down every time the main host they talked to through HttpClient \
went down because they had their max-total-connections set too high.

I'm from the school of thought where putting a hard limit on these types of expensive \
transactions is a very good thing.  If you're working on a system that's dependent on \
10 other systems, the worst thing you can do is tune your system such that your \
entire system goes down every time any of those 10 systems goes down.

My suggestion is to determine what you think your true max is.  I feel that the \
ultimate way to do this is to instrument your production system to tell you what \
maximum it actually reaches and monitor it under real load and go from there.  If \
you're unable to do that, you can calculate it.  This depends on a lot of things only \
you will know depending on whether or not you're caching the HttpClient responses, \
how long they are cached, how many requests-per-second you need to do, etc.

In my case, and this might sound funny at first, my I also have my connection manager \
set the same way you do: ConnManagerParams.setMaxTotalConnections(httpParams, \
Integer.MAX_VALUE);

But this is because I have host-specific tunings for each HTTP host I talk to.  So \
while the "global" value is infinite, I have a max-connections for every different \
host that effectively sets the max-total-connections to the sum of all of my \
host-specific max-connections values.  I like this level of granularity because, in \
my case, some of the HTTP resources I talk to the least often are also the most \
fragile, and I can limit their impact on my system when they get sick without \
effecting the bulk of off-host HTTP traffic I generate.

Hope this helps,
Mike

--- On Sun, 9/5/10, mrbeagle <jiminoc@gmail.com> wrote:

> From: mrbeagle <jiminoc@gmail.com>
> Subject: What is the determining factor for Max Connections?
> To: httpclient-users@hc.apache.org
> Date: Sunday, September 5, 2010, 5:56 PM
> 
> I have a server app that currently has 100 worker threads
> that fetch data
> from links. Currently I have
> 
> ConnManagerParams.setMaxTotalConnections(httpParams,
> Integer.MAX_VALUE);
> 
> but I'm curious what I should be setting that to and I'm
> not sure I know
> what factors go into deciding that number, ram? network
> bandwidth? cpu? 
> 
> Whats the rule of thumb for determining the optimal number
> for your app?
> 
> thanks
> -- 
> View this message in context: \
> http://old.nabble.com/What-is-the-determining-factor-for-Max-Connections--tp29627879p29627879.html
>  Sent from the HttpClient-User mailing list archive at
> Nabble.com.
> 
> 
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