Apache config SetEnv variable only if not set

Question

I have a fairly high traffic web server and would like to squeeze some micro optimization out of it.

In Apache's config I have:

SetEnvIfNoCase Request_URI "\.a?png$" dontlog SetEnvIfNoCase Request_URI "\.bmp$" dontlog SetEnvIfNoCase Request_URI "\.css$" dontlog ...several more 

I'd like to achieve this (pseudo-code):

<If env=!dontlog> SetEnvIfNoCase Request_URI "\.a?png$" dontlog </If> <If env=!dontlog> SetEnvIfNoCase Request_URI "\.bmp$" dontlog </If> <If env=!dontlog> SetEnvIfNoCase Request_URI "\.css$" dontlog </If> ...several more 

Performing a config test using my pseudo-code results in:

AH00526: Syntax error on line 260 of C:/apache24/conf/httpd.conf: Cannot parse condition clause: syntax error, unexpected T_OP_STR_EQ, expecting '('

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Note:

Please ignore the regex triviality of the examples. How can I perform short-circuiting?

Answer 1

SetEnvIfNoCase performs regular expression matching in a case-insensitive manner.

So rather than finding a complex work-around to avoid processing separate SetEnvIfNoCase tests and multiple trivial regular expressions, reduce your test to a single, slightly more complex, regular expression that matches all file extensions you don't want to log.

SetEnvIfNoCase Request_URI "\.(?:jpe?g|css|bmp|a?png)$" dontlog 

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Also consider storing and serving your images in a separate subdomain. If you believe logging an unnecessary performance penalty, that allows you to configure a VirtualHost without any logging, which then completely avoids the need for separate testing if a request should or shouldn't be logged.

People claim that an images / static content subdomain will improve pagespeed because a browser can open additional connections to the subdomain, you don't have to set/process cookies there etc. etc. And even if you don't want to use a CDN for your main site, you can still easily use one for your static content.