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From "Houser, Rick" <rick.hou...@jackson.com>
Subject RE: [users@httpd] Problems with Event MPM Performance Tuning in 2.4.18
Date Tue, 31 May 2016 16:49:33 GMT
Thank you very much for the quick response, Luca.

It definitely sounds like that could be related to the problems I’m having.  Looking at
the patch, however, both the original and the replacement seem to be enforcing a minimum value
to MinSpareThreads that would correspond to at least one completely idle process.  From my
perspective, I think that is contradicting the documentation provided for Max/MinSpareThreads
and preventing me from spawning additional processes only when the existing ones start to
become full.

I’m going to dive into that specific section of code further and see if I can’t dig something
up.


Rick Houser
Web Administration
(517)367-3516

From: Luca Toscano [mailto:toscano.luca@gmail.com]
Sent: Tuesday, May 31, 2016 11:02
To: users@httpd.apache.org
Subject: Re: [users@httpd] Problems with Event MPM Performance Tuning in 2.4.18

Hi Rick!

2016-05-31 15:57 GMT+02:00 Houser, Rick <rick.houser@jackson.com<mailto:rick.houser@jackson.com>>:

I have to deal with mod_cluster, and it is extremely memory hungry (in the GB range per process).
 As mitigation, I’m trying to get down to a single apache worker process per host when we
aren’t under heavy load.  That would save me about 6GB per host.



We have several hosts running the exact same thing behind a load balancer and I’ve never
seen a crash, so I’m not concerned with running a single instance.  Running 4 20 thread
instances is almost 4 times the memory of this one instance, for example.





This is the relevant portion of the configuration:



LoadModule mpm_event_module modules/mod_mpm_event.so

ServerLimit 8

StartServers 1

ThreadLimit 80

ThreadsPerChild 80

MaxRequestWorkers 640

MaxSpareThreads 120

MinSpareThreads 8







The top of mod-Status:



Apache Server Status for HOSTNAME (via 10.X.X.X)

Server Version: CUSTOMSTRING/2.4.18 (Unix) OpenSSL/1.0.1e-fips mod_cluster/1.3.1.Final

Server MPM: event

Server Built: Dec 16 2015 16:07:29

________________________________________

Current Time: Tuesday, 17-May-2016 14:37:00 EDT

Restart Time: Monday, 02-May-2016 09:36:16 EDT

Parent Server Config. Generation: 10

Parent Server MPM Generation: 9

Server uptime: 15 days 5 hours 44 seconds

Server load: 0.72 0.75 0.89

Total accesses: 39007867 - Total Traffic: 1.7 GB

CPU Usage: u2533.2 s168.49 cu0 cs0 - .206% CPU load

29.7 requests/sec - 1364 B/second - 45 B/request

5 requests currently being processed, 155 idle workers

PID         Connections       Threads                Async connections

                total       accepting             busy      idle         writing  keep-alive
          closing

11397    35           yes         2              78           0              33          
0

29323    26           yes         3              77           0              23          
0

Sum       61                          5              155         0              56       
   0

................................................................

................________________________________________________

_______W____W___________________................................

................................................____________W___

______W__________________________________W______________________

................................................................

................................................................

................................................................

................................................................

................................................................





The idle threads here usually stays around the mid 150s.  These particular workers were started
about 40 minutes apart, but I have the similar pattern showing in other regions with similar
start times and the same workers being up for over a month.



Given the MaxSpareThreads 120, I would expect this to drop the second worker fairly quickly
and work as described (https://httpd.apache.org/docs/2.4/mod/mpm_common.html#maxsparethreads).
 But, that’s not happening and I'm stuck with two processes handling the load.  It's acting
almost as if there is a "ServerMin 2" directive hard-coded or something.



This certainly looks like a bug (whether in the documentation or the code itself).  Any suggestions
on how to get this to work before I submit a bug ticket?


IIRC we had a similar issue earlier on in this email list:

https://www.mail-archive.com/users@httpd.apache.org/msg60181.html

Afaik the fix has not been ported to the 2.4.x branch yet.. If this is what you are experiencing,
we'll follow up with the devs to check what is the status of the backport proposal.

Let me know!

Luca


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