"RewriteMap"s inefficient (was: [Zope-dev] Apache Mod_rewrite question)

[Dieter Maurer]

Ganesha Shanmuganathan wrote at 2004-7-13 16:40 -0500:
> ...
>The directive RewriteMap has unexpected behavior when it is used to
>define more than one map with same map name in diffrent places. Normally
>all the directives within a tag applies only to that tag. 

There are more strange things with Apache's "RewriteMap"s.
Be warned: they are very inefficiently implemented for large maps!

  We used such maps to let Apache serve static CMF content
  as folkore reports that Apache is an order of magnitude
  faster than Zope in serving static content.

  It turned out that the solution using Apache RewriteMaps was 
  slower than directly serving this content from Zope --
  by a factor of 5!

  The explanation: Apache caches only single successful lookups
  in the map file. Each access to a key not in the cache
  results in parsing the map file until the key is found -- the
  whole map file when it does not contain the key.
  For larger map files, this has desastrous effects.

Now, we use RewriteMaps only when the map files are very small
(not more than some dozen entries).

> ... maps with the same name ...
>The problem is the cache treats both the file as the same since they
>have the same name! Hence if you visit foo.com first, the data stored in
>foomap.txt is returned from the cache next time you visit foo.com or
>bar.com. This causes apache to redirect into the wrong zope site.

We did not observe this behaviour...

-- 
Dieter