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Our Heroku app went down for a period of time yesterday. The error message in our logs:

[error] server reached MaxClients setting, consider raising the MaxClients setting

I checked the httpd.conf to see what the MaxClients setting was, and this is what I found:

MaxClients 1

The commit that added these directives is on Heroku's Github. Does there appear to be a rationale for a MaxClients setting of 1, or is it simply arbitrary? Are there any considerations I should make when increasing it?

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How did you change this parameter sir? –  Burak Jan 30 '13 at 22:56
You fork the Heroku PHP Buildpack and edit the conf/httpd.conf file. –  Brad Koch Jan 30 '13 at 23:01

2 Answers 2

up vote 2 down vote accepted

Heroku dynos are designed to be a single unit of computation. For comparison:

A single-threaded, non-concurrent framework like Rails can process one request at a time.

Setting MaxClients 1 is simply telling your PHP dyno to only handle its one request at a time. Since the dyno is actually capable of handling many more requests that that, MaxClients can and should be raised to a number much larger, such as 256.

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Here explaint mean MaxClients: http://httpd.apache.org/docs/2.2/mod/mpm_common.html#maxclients

Try increase parameter about 250 and retry

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I understand MaxClients is too low. I'm trying to understand the why - why is the default setting 1, and what implications does that entail for changing it? –  Brad Koch Aug 9 '12 at 14:55
You'll have to ask whoever checked in the code. And the implications is that the server will only handle one simultaneous connection, which is very close to pointless. –  Michael Hampton Aug 13 '12 at 21:09

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