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Bug #63395 Spawned processes do not perform
Submitted: 2012-10-30 10:20 UTC Modified: 2021-12-09 22:16 UTC
Avg. Score:4.4 ± 0.9
Reproduced:13 of 13 (100.0%)
Same Version:3 (23.1%)
Same OS:3 (23.1%)
From: Alex at phpguide dot co dot il Assigned: bukka (profile)
Status: Closed Package: FPM related
PHP Version: 5.4.8 OS: Ubuntu 12.04 x64
Private report: No CVE-ID: None
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 [2012-10-30 10:20 UTC] Alex at phpguide dot co dot il
I'm running nginx 1.2.4 with php5-fpm (5.4.8) issuing

 ab -n 20000 -c 1000 http://localhost/index.php


pm = dynamic
pm.max_children = 3000
pm.start_servers = 100  <- this is important
pm.max_spare_servers = 1000

I'm having a lot of errors in nginx talking to php

[error] 26125#0: *49177 upstream prematurely closed connection while reading 
response header from upstream, ... "fastcgi://"

[error] 26125#0: *56030 recv() failed (104: Connection reset by peer) while 
reading response header from upstream, ... upstream: "fastcgi://"

The fpm log shows a lot of 

WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or 
pm.min/max_spare_servers), spawning 32 children, there are 0 idle, and X total 

When spawning new children reaches a concrete amount nginx stops issuing such 
errors. This leads me to believe freshly spawned processes do not execute and 
respond correctly.

Now, when I start with 3000 children straight ahead, all connections work 
properly. No errors in nginx or fpm.

pm = dynamic
pm.max_children = 3000
pm.start_servers = 3000  <- Straight ahead
pm.max_spare_servers = 3000

Test script:
The php code on the server is relatively simple.

apc_inc('count111'); sleep(1); echo 'x';


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 [2013-02-13 09:50 UTC] php-bugs at puzzled dot xs4all dot nl
This bug seems similar to
 [2014-04-15 07:39 UTC] roger dot qiu at polycademy dot com
Yep this is definitely a bug. I experienced the same thing.

Basically if you have NGINX with upstream keepalive, and if this number is > than the pm.max_children in FPM, then what happens is that, if there is a X amount of concurrent requests (from for example Apache Bench), in which X is greater than the pm.max_children, this will result in Apache Bench freezing and sometimes never completing certain requests.

If the keepalive number is lower than the max_children (not equal), this problem then doesn't exist.
 [2017-11-30 17:19 UTC] federico dot omoto at gmail dot com
This is a really old bug that is affecting PHP versions <= 7.2.0.
Can we expect it to be fixed soon?
 [2021-12-09 22:16 UTC]
-Status: Open +Status: Closed -Assigned To: +Assigned To: bukka
 [2021-12-09 22:16 UTC]
There's no a configuration option pm.max_spawn_rate (introduced in PHP 8.1) that allows customizing the rate and preventing this problem. Please see more details in
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