[转]Nginx hash Module

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导读：

　　本模块由第三方提供，不包含在 Nginx 的源码发布版中。安装介绍等请看 这里.

　　The upstream_hash module provides simple upstream load distribution by hashing a configurable variable (e.g., the request URI, incoming HTTP headers, or some combination). Example usage:

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　　upstream backend {

server server1;

server server2;

hash $request_uri;

}



　　Here, Nginx will choose server1 or server2 by hashing the request URI ($request_uri).

　　指令

　　hash

　　hash_method

　　hash_again

　　hash

　　语法： hash $variable

　　作用域： upstream

　　Enables upstream hashing of $variable.

　　When present, the "server" directives cannot take any arguments ("weight", "max_fails", etc.).

　　hash_method

　　语法： hash_method [ crc32 | simple ]

　　默认值： simple

　　作用域： upstream

　　The hash algorithm to use. "crc32" takes the last 15 bits of the crc32 value and modulo's by the number of servers. (This behavior is compatible with libmemcache.) "simple" is described below.

　　hash_again

　　语法： hash_again number

　　默认值： 0

　　作用域： upstream

　　Number of times to rehash the value and choose a different server if the backend connection fails. Increase this number to provide high availability.

　　Installation

　　This module is not distributed with the Nginx source. You can download the request_hash module here: nginx_upstream_hash-0.2.tar.gz

　　After extracting, you will need to patch the latest Nginx source (0.5.21 as of this writing). Run patch like this:

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　　cd nginx-0.5.21

patch -p0


　　Then add the following option to your Nginx ./configure command:

　　1--add-module=path/to/upstream/hash/directory



　　Then "make" and "make install" as usual.

　　The "simple" hash algorithm

　　The "simple" hash algorithm is the same as that used for Nginx's internal hash tables. The function is:

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　　#define ngx_hash(key, c) ((u_int) key * 31 + c)



u_int ngx_hash_key(u_char *data, size_t len)

{

u_int i, key;



key = 0;



for(i = 0; i <len i><br>key *= 31; <br><br>key += data;<br><br> }<br><br><br><br><strong>return</strong>key;<br><br>}<br><br><br><br>　　The hash value is then modulo'd by the number of servers, and thus a server is picked. A server's index is determined by the order in which it appears in the upstream block.<br><br><br><br>本文转自<br><br><a href="http://anotherbug.blog.chinajavaworld.com/entry/4298/0/">http://anotherbug.blog.chinajavaworld.com/entry/4298/0/</a><br></len>