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Adjusting child processes for PHP-FPM (Nginx)

Adjusting child processes for PHP-FPM (Nginx)

When setting these options consider the following:

  • How long is your average request?
  • What is the maximum number of simultaneous visitors the site(s) get?
  • How much memory on average does each child process consume?

Determine if the max_children limit has been reached.

  • sudo grep max_children /var/log/php?.?-fpm.log.1 /var/log/php?.?-fpm.log

Determine system RAM and average pool size memory.

  • free -h
  • All fpm processes: ps -ylC php-fpm7.0 --sort:rss
  • Average memory: ps --no-headers -o "rss,cmd" -C php-fpm7.0 | awk '{ sum+=$1 } END { printf ("%d%s\n", sum/NR/1024,"M") }'
  • All fpm processes memory: ps -eo size,pid,user,command --sort -size | awk '{ hr=$1/1024 ; printf("%13.2f Mb ",hr) } { for ( x=4 ; x<=NF ; x++ ) { printf("%s ",$x) } print "" }' | grep php-fpm

Calculate max_children

Based on RAM

  • pm.max_children = Total RAM dedicated to the web server / Max child process size

  • System RAM: 2GB

  • Average Pool size: 85Mb

  • pm.max_children = 1500MB / 85MB = 17

Based on average script execution time

  • max_children = (average PHP script execution time) * (PHP requests per second)
  • visitors = max_children * (seconds between page views) / (avg. execution time)

Configure

sudo vim /etc/php/7.0/fpm/pool.d/www.conf

pm.max_children = 17
pm.start_servers = 2
pm.min_spare_servers = 1
pm.max_spare_servers = 3
pm.max_request = 1000
; Choose how the process manager will control the number of child processes.
; Possible Values:
;   static  - a fixed number (pm.max_children) of child processes;
;   dynamic - the number of child processes are set dynamically based on the
;             following directives:
;             pm.max_children      - the maximum number of children that can
;                                    be alive at the same time.
;             pm.start_servers     - the number of children created on startup.
;             pm.min_spare_servers - the minimum number of children in 'idle'
;                                    state (waiting to process). If the number
;                                    of 'idle' processes is less than this
;                                    number then some children will be created.
;             pm.max_spare_servers - the maximum number of children in 'idle'
;                                    state (waiting to process). If the number
;                                    of 'idle' processes is greater than this
;                                    number then some children will be killed.
; Note: This value is mandatory.
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