This document describes srcache-nginx-module v0.23

(<https://github.com/agentzh/srcache-nginx-module/tags>) released on 27

October 2013.

Cache Key Preprocessing

It is often desired to preprocess the cache key to exclude random noises

that may hurt the cache hit rate. For example, random session IDs in the

URI arguments are usually desired to get removed.

Consider the following URI querystring

SID=BC3781C3-2E02-4A11-89CF-34E5CFE8B0EF&UID=44332&L=EN&M=1&H=1&UNC=0&SRC=LK&RT=62

we want to remove the "SID" and "UID" arguments from it. It is easy to

achieve if you use [[HttpLuaModule]] at the same time:

location = /t {

rewrite_by_lua '

local args = ngx.req.get_uri_args()

args.SID = nil

args.UID = nil

ngx.req.set_uri_args(args)

';

echo $args;

}

Here we use the echo directive from [[HttpEchoModule]] to dump out the

final value of $args in the end. You can replace it with your

[[HttpSRCacheModule]] configurations and upstream configurations instead

for your case. Let's test this /t interface with curl:

$ curl 'localhost:8081/t?RT=62&SID=BC3781C3-2E02-4A11-89CF-34E5CFE8B0EF&UID=44332&L=EN&M=1&H=1&UNC=0&SRC=LK'

M=1&UNC=0&RT=62&H=1&L=EN&SRC=LK

It is worth mentioning that, if you want to retain the order of the URI

arguments, then you can do string substitutions on the value of $args

directly, for example,

location = /t {

rewrite_by_lua '

local args = ngx.var.args

newargs, n, err = ngx.re.gsub(args, [[\b[SU]ID=[^&]*&?]], "", "jo")

if n and n > 0 then

ngx.var.args = newargs

end

';

echo $args;

}

Now test it with the original curl command again, we get exactly what we

would expect:

RT=62&L=EN&M=1&H=1&UNC=0&SRC=LK

But for caching purposes, it's good to normalize the URI argument order

so that you can increase the cache hit rate. And the hash table entry

order used by LuaJIT or Lua can be used to normalize the order as a nice

side effect.

example, the version 1.4.3 (see Nginx Compatibility),

4.2-upstream_truncation.patch (you do NOT need this patch if you are

using nginx 1.5.3 and later versions.)

wget 'http://nginx.org/download/nginx-1.4.3.tar.gz'

tar -xzvf nginx-1.4.3.tar.gz

cd nginx-1.4.3/

* 1.4.x (last tested: 1.4.3)