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I have about 6000 URLs that need to be redirected after changing the CMS. All those URLs are stored in a DB table together with an ID that allows me to tell what is being referenced. Using this table I could generate one huge .htaccess with a lot of Rewrite rules but I suspect that is very inefficient. What's the best way to go? As far as I can tell there are two options:

  • Using a RewriteMap where the key is the old URL (it contains no ID, just text, so it has to be the whole thing). I wonder if having 100-150 char long keys is gonna work well.
  • Generating a DB table that exactly matches every old/new URL pair and calling some small script to make the redirect.

(Could be summed up as: Is a hash map stored in the filesystem more efficient than a indexed DB table?)

Second part of the question. The new URLs contain the ID of the page being invoked. Something like

www.example.com/abc/21-defghi.html

If instead I call

www.example.com/21-xxx.html

I get a 301 Redirect to the correct URL. Should I bother to generate the exact new URL or is it ok to concatenate two redirects? This means either storing just an ID or the whole new URL.

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up vote 3 down vote accepted

Creating a huge .htaccess can have a serious performance impact on your system as it is read linearly for all requests, at least until a rule with the L attribute (Last Rule) is matched.

The way I did something similar (about 3000 redirects) is to put a custom error page in the .htaccess. From memory the syntax is something like this:

ErrorDocument 404 404.php

Then in 404.php, implement the logic using a MySQL database, searching for the new URL using the requested URL. If it is found, redirect the request using the PHP location header, if not, then display a custom error page.

Unlike simply issuing the 404 redirect in the .htaccess, the 404.php file can keep track of requests and keep stats on the redirects being returned.

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Do you have any data on performance? i.e. How much slower than a "normal" request is it? –  Omar Kohl Jul 24 '11 at 19:40
    
It is easy to measure but it will completely depend on your server configuration, file-system cache including other activities happening on the server (since they compete with the FS cache). Just fill a .htaccess of a few thousand rules (they do not even have to apply) and see if you can measure a change in your server. With the 404 approach, the lookup only happens when something is not found. –  Itai Jul 24 '11 at 21:12
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