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bcremer opened this issue May 13, 2024 · 3 comments
Open

FPM Status: active processes greater than pm.max_children #14212

bcremer opened this issue May 13, 2024 · 3 comments
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@bukka
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Bug SAPI: fpm Status: Needs Triage

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@bcremer
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bcremer commented May 13, 2024 •
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Description

Given the following FPM Pool configuration the Pool is configured using 1500 static workers and a listen.backlog of 100:

$ cat /etc/php/8.3/fpm/pool.d/backoffice.conf 
[backoffice]
listen = /run/php8.3-fpm_backoffice.sock
listen.backlog = 100

pm = static
pm.max_children = 1500
pm.status_path = /php8.3-fpm-status-backoffice.php

; The number of requests each child process should execute before respawning. This can be useful to work around memory leaks
pm.max_requests = 2000

The listen.backlog works like expected on the socket.

$ ss -lxn src ==  /run/php8.3-fpm_backoffice.sock
Netid                      State                       Recv-Q                      Send-Q                                                              Local Address:Port                                              Peer Address:Port                      Process
u_str                      LISTEN                      0                           100                                               /run/php8.3-fpm_backoffice.sock 47129                                                        * 0

Without high traffic total processes reports 1500 as expected.

$ curl -s 127.0.0.1:80/php8.3-fpm-status-backoffice.php
pool:                 backoffice
process manager:      static
start time:           13/May/2024:04:02:02 +0200
start since:          22533
accepted conn:        3057525
listen queue:         0
max listen queue:     0
listen queue len:     0
idle processes:       1460
active processes:     40
total processes:      1500
max active processes: 549
max children reached: 0
slow requests:        0

When generating high concurrent requests using a tool like siege or k6 I can observe the following output from the status page:

$ curl 127.0.0.1:80/php8.3-fpm-status-backoffice.php
pool:                 backoffice
process manager:      static
start time:           08/May/2024:04:02:01 +0200
start since:          19565
accepted conn:        10120636
listen queue:         0
max listen queue:     0
listen queue len:     0
idle processes:       1
active processes:     3347
total processes:      3348
max active processes: 3503
max children reached: 0
slow requests:        0

active processes/total processes/max active processes are way over the defined pm.max_children = 1500.

How can active processes be greater than pm.max_children?

Also max children reachedreports 0.

Relates to: #9943 (comment)

PHP Version

PHP 8.3.6

Operating System

Debian 11
@bcremer
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bcremer commented May 13, 2024

Maybe related:

I can also observe that the number of requests I can measure via the FPM access.log does not match the delta for accepted conn for a given timespan.

The accepted conn delta is approx double the abount of requests shown in the fpm access log.

@fcoelho fcoelho mentioned this issue Jul 19, 2024
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@txuna
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txuna commented Jun 2, 2025

@bcremer Is it still occurring?

@s2x
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s2x commented Jun 3, 2025

I also have the same problem. We wanted to use this metric to scale pods but unfortunately it returns incorrect results.

fpm settings:

pm = static
pm.max_children = 20

version: PHP 8.4.7 (fpm-fcgi) (built: May 8 2025 21:27:16) (NTS)

can be reproduced by sending large traffic to status php-fpm endpoint

no-load status
pool: www
process manager: static
start time: 03/Jun/2025:13:11:48 +0000
start since: 23846
accepted conn: 154295
listen queue: 0
max listen queue: 20
listen queue len: 4096
idle processes: 19
active processes: 1 --- one active for status page
total processes: 20  --- this is fine
max active processes: 1597
max children reached: 0
slow requests: 0
memory peak: 14680064

when we run wrk http://localhost/status

pool: www
process manager: static
start time: 03/Jun/2025:13:11:48 +0000
start since: 23914
accepted conn: 158110
listen queue: 0
max listen queue: 20
listen queue len: 4096
idle processes: 0
active processes: 698
total processes: 698 --- sooo big number
max active processes: 1597
max children reached: 0
slow requests: 0
memory peak: 14680064

The number of php processes, checked with the ps command, is correct, so the problem is probably with the display.

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@bcremer @bukka @s2x @devnexen @txuna