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From Rajalakshmi Iyer <...@blismedia.com>
Subject Help needed with Event MPM configuration settings
Date Tue, 04 Nov 2014 13:05:49 GMT
Hello,

I need some assistance with tuning Apache with event MPM.

The Apache server in consideration is running an application module. The
current MPM settings are -

<IfModule mpm_event_module>
    StartServers             2
    ServerLimit              4
    MinSpareThreads         60
    MaxSpareThreads         240
    MaxClients              240
    ThreadsPerChild         60
    MaxRequestWorkers       240
    MaxConnectionsPerChild   0
    MaxRequestsPerChild      0
</IfModule>

This means that there are 240 threads available to work on 240 established
connections.

The AsyncRequestWorkerFactor for event MPM is 2 by default.

So, based on http://httpd.apache.org/docs/current/mod/event.html, the
server can accept at the most *(AsyncRequestWorkerFactor + 1) *
MaxRequestWorkers*, i.e. 720 maximum concurrent connections.

The process will accept new connections only when current number of
connections is lower than *ThreadsPerChild + (AsyncRequestWorkerFactor *
number of idle workers) *

Assuming the server is always under heavy load, the 240 worker threads are
busy working on 240 requests from 240 established connections. As soon as
they finish their work, they will be working on the subsequent requests on
the same connection.

There are 720 connections that have been accepted by the server, but only
240 of those have been worked upon. The remaining 480 will never get a
chance, because there are subsequent requests on the same connection to be
worked upon.

As it stands today, the symptoms observed are --

   1. The server is not responding to new connections
   2. The 8 core server machine shows that 80% of each of the 8 cores is
   idle, which means that the workers are not really doing much. Does that
   mean that each of the 240 threads when allocated a connection is waiting
   for requests on that connection and not picking up other connections that
   are newly established?

Any help around what settings can be modified to alleviate these symptoms
would be useful.

Thanks
Raj

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