From: spiralofhope <spiralofhope@...>
Date: 2009-09-01T15:20:36+09:00
Subject: Re: Best Practice for Multiline Regexps

On Tue, 1 Sep 2009 14:55:08 +0900
Robert Klemme <shortcutter@googlemail.com> wrote:

> > 1) Read file to String, match string against first pattern, read
> > next file into String, match with same pattern... once I've gone
> > through all the files with the first pattern, start over with the
> > next pattern.  
> 
> That's the worst you can do.


> > 2) Read file to String, match whole string against all 20 patterns,
> > go to next file, match against 20 patterns...  
> 
> Most efficient of the simple approaches.

Robert is right from a hard drive perspective.

To understand why method 2 works well - just remember that when a file
is read from your disk, it is cached.  Your first solution would force
the system to cache file 1, process it, then cache file 2 to process
it.. through to caching file n and then back to file 1 again, cycling
through each pattern you're searching for for every file.  It would be
horribly taxing on disk access.

But if we imagine that all the files are on a ramdisk, then could the
first method possibly be better?  Something in the back of my mind
says method 2 is still better.


-- 
http://spiralofhope.com