why nginx just use 511 for listen backlog

[Igor Sysoev]

On Tue, Sep 29, 2009 at 11:32:32AM -0400, zhijianpeng wrote:

> I found that :
> 
> #define NGX_LISTEN_BACKLOG 511
> 
> and use it as the backlog of  listen()
> 
> ls.backlog = NGX_LISTEN_BACKLOG;
>  if (listen(s, ls.backlog) == -1) {
> 
> Does  it mean that only 511 connection could  be accept at the same time ?

No, it means that up to 511 connections can be queued in kernel listen
queue.  511 is just a safe limit for the most OSes. For FreeBSD it's -1,
i.e., value of sysctl kern.ipc.somaxconn.

> May   I modify it to 1024 or higher( I am sure use it less than  SOMAXCONN )

     listen  80  default  backlog=1024;


-- 
Igor Sysoev
http://sysoev.ru/en/