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Re: how is grep so fast?

From: Edward Peschko
Subject: Re: how is grep so fast?
Date: Mon, 8 Jun 2009 10:12:51 -0700

> This seems strange indeed. I can only reproduce similar behaviour when
> searching a large binary file; in the matching cases, where the whole
> file is not read by grep, it is of course fast. But in other cases this
> should not happen. What exactly was the "whole grep run"?

The 'whole grep run' was searching for a fixed substring on a large
 (500 MB) file. Even a regex search was faster than the simple fread
loop I had below.

If I switch out 'read' for 'fread'  in the loop before then it gets
*lots* faster -
but I was exceedingly surprised that there was a 300 percent
 performance penalty. getline is hopeless, too in terms of performance.
All of this BTW was on an EC2 centos instance.


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