Processing too slow with loop Post: 302976084

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Top Forums Shell Programming and Scripting Processing too slow with loop Post 302976084 by stomp on Thursday 23rd of June 2016 03:06:26 PM

06-23-2016

Registered User

If the patterns are always fixed strings the usage of fgrep or grep -F may result in a HUGE Performance Boost.

If possible, run fgrep without -i. That'll get you another Performance Boost and also put LANG=C before the fgrep command, which should speed up things a little too.

Sidenote

There was a scripting task request in the german linux forum(www.linuxforen.de) here: Linuxforen.de Thread regarding fgrep

The task was similar. The big file had 5.000.000 lines (300 MB). The smaller file had 100.000 lines (3 MB). The results:

Winner fgrep: 7 Seconds
extremeley optimized lua script: 8,6 Seconds
awk-Script: ~97 hours (obviously the great awk-hackers here would get a whole lot more out of awk)
regular grep: stopped after 45 Minutes runtime and 12 GB RAM-Usage

I think the situation is not so far away from this situation here. I suppose the smaller file here is a lot smaller, so the task will not be as cpu-intensive as the other one but this task has a lot more to read(5-6 GB as said by the nikhil).

Last edited by stomp; 06-23-2016 at 08:43 PM..

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LEARN ABOUT OPENDARWIN

zgrep

ZGREP(1)						      General Commands Manual							  ZGREP(1)

NAME

       zgrep - search possibly compressed files for a regular expression

SYNOPSIS

       zgrep [ grep_options ] [ -e ] pattern filename...

DESCRIPTION

       Zgrep  is used to invoke the grep on compress'ed or gzip'ed files. All options specified are passed directly to grep.  If no file is speci-
       fied, then the standard input is decompressed if necessary and fed to grep.  Otherwise the given files are uncompressed	if  necessary  and
       fed to grep.

       If  zgrep  is invoked as zegrep or zfgrep then egrep or fgrep is used instead of grep.  If the GREP environment variable is set, zgrep uses
       it as the grep program to be invoked. For example:

	   for sh:  GREP=fgrep	zgrep string files
	   for csh: (setenv GREP fgrep; zgrep string files)

AUTHOR

       Charles Levert (charles@comm.polymtl.ca)

SEE ALSO

       grep(1), egrep(1), fgrep(1), zdiff(1), zmore(1), znew(1), zforce(1), gzip(1), gzexe(1)

																	  ZGREP(1)