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Thundering herd in Nginx

在下面文章中，对Nginx解决"Thundering herd"的方法进行了解释:

nginx Inside NGINX: How We Designed for Performance & Scale

The NGINX worker processes begin by waiting for events on the listen sockets (accept_mutex and kernel socket sharding).

Core functionality # accept_mutex

If accept_mutex is enabled, worker processes will accept new connections by turn. Otherwise, all worker processes will be notified about new connections, and if volume of new connections is low, some of the worker processes may just waste system resources.

There is no need to enable accept_mutex on systems that support the EPOLLEXCLUSIVE flag (1.11.3) or when using reuseport.

Prior to version 1.11.3, the default value was on.

nginx Socket Sharding in NGINX Release 1.9.1

NGINX 1.9.1 introduces a new feature that enables use of the SO_REUSEPORT socket option, which is available in newer versions of many operating systems, including DragonFly BSD and Linux (kernel version 3.9 and later). This socket option allows multiple sockets to listen on the same IP address and port combination. The kernel then load balances incoming connections across the sockets.

nginx Performance Tuning – Tips & Tricks

accept_mutex off – All worker processes are notified about new connections (the default in NGINX 1.11.3 and later, and NGINX Plus R10 and later). If enabled, worker processes accept new connections by turns.

We recommend keeping the default value (off) unless you have extensive knowledge of your app’s performance and the opportunity to test under a variety of conditions, but it can lead to inefficient use of system resources if the volume of new connections is low. Changing the value to on might be beneficial under some high loads.

stackoverflow Why is 'accept_mutex' 'on' as default in Nginx?

A

As of nginx mainline version 1.11.3 (released 2016-07-26), accept_mutex now defaults to off. This is partly because the new EPOLLEXCLUSIVE flag provides the benefits of accept_mutex without the extra overhead.

A

Check the

  • accept Serialization - Multiple Sockets
  • accept Serialization - Single Socket

sections of this Apache documentation. https://httpd.apache.org/docs/2.4/misc/perf-tuning.html. (This doc matters most, compared to the rest of 2 I posted)

It's very inspiring and I also read the

http://nginx.org/en/docs/ngx_core_module.html#accept_mutex explaination as well as https://www.nginx.com/blog/performance-tuning-tips-tricks/ (search page with accept_mutex).

Aftering reading all of these, I guess Nginx is very similar to Apache in this aspect.