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I am running a Linux Centos/Plesk box with a medium/high traffic Prestahop e-commerce website.

I use the stock-Plesk configuration with PHP 7.0 FPM served by Apache / Nginx as a reverse proxy. I only made some tweaks on FPM pool settings according to the server power basically to increase MaxChildren value to serve more requests.

From some days I am encountering occasional website slowdowns that I am trying to troubleshoot (website did not have any particular visits increases in last time).

I have already performed some checks on: - server logs, can't see particular error_logs - server load average (it is ok) - I/O "wa" value is OK - MySQL server has not slow queries during slowdowns (SHOW FULL PROCESSLIST is never returning long execution time queries) - net stat (no DDOS / strange connections)

I installed mod_status form Apache and noticed from the server-status page that during slowdowns I have a high number of "requests currently being processed" in "W" status [sending reply] (During slowdowns I can have up to 70/80 of those requests for several seconds) so I can correlate the slowdowns to Apache being busy to deliver requests but I can't figure out why and what application/webpage component is the source of the problem.

My question here is some advice on how to understand the culprit of slowdowns (a PHP script ? a stuck external service during Apache request ?)

thank you.

Keyur
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gennaris
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  • Do you have any kind of logging in your application that you can put on? – Jeroen Heier Jul 08 '17 at 07:26
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