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From Leif Hedstrom <zw...@apache.org>
Subject Re: basic regex_map vs map performance
Date Thu, 14 Jul 2016 17:21:18 GMT

> On Jul 14, 2016, at 12:41 AM, tomr <tom@equalit.ie> wrote:
> 
> Hi All,
> 
> Simple perf question, hopefully easy enough to answer that I don't need to spin up a
test environment!
> 
> My options are:
> 
> map  http://site.com      http://origin.site.com
> map  http://www.site.com  http://origin.site.com
> 
> vs...
> 
> regex_map http://^(www\.)?site\.com$/  http://origin.site.com
> 
> We have approx 1000 similar rules. Intuitively I would guess that using 2 map rules each
time would be a performance win over using a single regex_map rule. Is that likely to be:


Very likely correct. The host lookups are very fast, because of the hash map. But if you only
have one regex rule like that, the performance impact is likely so small that it’s worth
having that simpler rule just for ease of use and management. The PCRE’s are still pretty
fast.

The caveat here is that you have a lot of regexes, you might end up evaluating many of them,
so the order of the regexes can have a big impact on performance (i..e put the one most likely
to match first in remap.config).

I believe Bryan and Phil made some performance improvements with PCRE’s, so if your platform
has a modern PCRE library, it will be able to use the JIT that it supports.

Cheers,

— Leif


> - correct?
> - incorrect?
> - "it depends" / not that simple and I really should test it?
> 
> Thanks in advance,
> Tom
> 
> 
> 


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