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Date: Thu, 23 Sep 2010 08:03:31 +0200
From: Ruediger Pluem <rpluem@apache.org>
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To: dev@httpd.apache.org
Subject: Re: svn commit: r1000130 -
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On 09/22/2010 08:59 PM, Jeff Trawick wrote:
> On Wed, Sep 22, 2010 at 2:37 PM, <trawick@apache.org> wrote:
> 
>> Author: trawick
>> Date: Wed Sep 22 18:37:16 2010
>> New Revision: 1000130
>>
>> URL: http://svn.apache.org/viewvc?rev=1000130&view=rev
>> Log:
>> follow up r956069 with additional clarifications
>> about the connection pool and related parameters
>> (yes, and fix part of those earlier "clarifications")
>>
>> Modified:
>>    httpd/httpd/trunk/docs/manual/mod/mod_proxy.xml
>>
>> Modified: httpd/httpd/trunk/docs/manual/mod/mod_proxy.xml
>> URL:
>> http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_proxy.xml?rev=1000130&r1=1000129&r2=1000130&view=diff
>>
>> ==============================================================================
>> --- httpd/httpd/trunk/docs/manual/mod/mod_proxy.xml (original)
>> +++ httpd/httpd/trunk/docs/manual/mod/mod_proxy.xml Wed Sep 22 18:37:16
>> 2010
>> @@ -764,13 +764,12 @@ expressions</description>
>>     using  <code>key=value</code> parameters, described in the table
>>     below.</p>
>>
>> -    <p>Setting <code>min</code> will determine how many connections to
>> -    the backend server will be retained after use.  Up to the
>> -    Soft Maximum, or <code>smax</code>, number of connections will be
>> -    created on demand.  Any connections above <code>smax</code> are
>> -    subject to a time to live, or <code>ttl</code>.  Apache httpd will
>> -    never create more than the Hard Maximum or, <code>max</code>,
>> -    connections to the backend server.</p>
>> +    <p>Setting <code>min</code> to non-zero allows connections to the
>> +    backend server to be retained after use;
> 
> 
> That last sentence is wrong, isn't it?  (I'm using the
> two-steps-forward/one-step-back approach until I can't go any further.  At
> least you don't have to look at the doc for apr_reslist_create() anymore ;)
> )
> 
> I honestly don't know what min is used for since we only create connections
> on demand, unless min=0 means don't retain, and min>0 means retain.
> 
> What I want to do as a user today: retain connections but don't use any if
> they've been idle for >= origin-server-keepalive seconds.
> 
> ttl is the only timeout avail, so that has to be set to the origin's
> keepalive timeout
> ttl only applies to connections above smax, so smax needs to be set as low
> as allowable

No. ttl is absolute. The resource list hands out no resources that have been
idle in the resource list for more then ttl. So no need to fiddle with
smax.
min only ensures that you always have at least min idle resources (of course
only if this does not increase the total number above hmax).
In the proxy case that does not mean that these resources have connections
to the backend. These are only created during their first real use.

So in short: Just set ttl to the keepalive of the backend minus some race seconds
for packet latency and don't care about the remaining stuff if don't want to
for other reasons.

Regards

R�diger