Plesk with LiteSpeed poor performance: Reached max children process limit, please increase LSAPI_CHILDREN

Symptoms

1. Plesk with LiteSpeed extension presents poor performance.

2. The LiteSpeed Apache error log /var/log/httpd/stderr.log shows a lot of errors like below:

   CONFIG_TEXT: Child process with pid: 3906418 was killed by signal: 15, core dump: 0
   [4015974] Reached max children process limit: 10, extra: 3, current: 13, busy: 13, please increase LSAPI_CHILDREN.

3. Websites' error logs like /var/www/vhosts/system/example.com/logs/error_log show:

   CONFIG_TEXT: [INFO] [3840776] [203.0.113.2:52353] Abort request processing by PID:3849827, kill: 1, begin time: 30, sent time: 30, req processed: 0
   [INFO] [3904563] [203.0.113.3:55639] Connection idle time: 121 while in state: 7 stream flag: 131072,close!
   ...
   [INFO] [3904563] [203.0.113.4:55639] Lsapi connection state: 3, watching event: 25, respState: 1, m_iTotalPending:0, m_iPacketLeft:0, m_iCurRespHeader:5, req sent for 121 seconds,Total processing time: 121.

Cause

LiteSpeed PHP limits exceeded.

Resolution

• Configure LiteSpeed PHP limits at Extension > LiteSpeed > LiteSpeed Configuration > WebAdmin Console based on the LiteSpeed documentation.
• To get assistance with the configuration, visit LiteSpeed website at https://www.litespeedtech.com/support to check available support options.