On a php5-fpm status page, what is the bottleneck that is preventing my server from
accept()'ing new sockets fast enough?
pool: www process manager: static start time: 20/Jan/2015:16:37:18 +0000 start since: 176705 accepted conn: 903749 listen queue: 0 max listen queue: 129 listen queue len: 128 idle processes: 59 active processes: 69 total processes: 128 max active processes: 128 max children reached: 0
As you can see, I've reached my listen queue, and this happens quite frequently. I understand the basic logic behind the listen queue, and it is laid out in some detail here: php-fpm status page: what are the "queue" items in this report?
I realize that I should increase the queue length, and I will make it so. However, my question is why is my listen queue filling up, and what is the bottleneck to prevent it from filling up in the first place? I assume if there is a large listen backlog, then there has to be something that isn't "keeping up"? Is this a CPU bottleneck / load issue that it cannot
accept() fast enough?