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looking behind in huge data files
Handling Huge Data example from a Well House Consultants training course
More on Handling Huge Data [link]
Source code: behind Module: P667
#!/usr/bin/env perl
# What lead up to a quote request? # See documentation after the Perl source while (<>) { next if (/googlebot/); # Eliminate quotes to spiders next if (/crawl/); next if (/spider/); next if (/inktomi/); if (m!GET /net/quote\.html!) { # is it a quote? ($host,$page) = (split)[0,6]; print "Host: $host\nQuote: $page\n"; foreach (@queue) { # If so, report on previous requests ($ohost,$opage) = (split)[0,6]; print "From: $opage\n" if ($host eq $ohost); } print "\n"; } else { next unless (m!T \S+\.(php|html)!); unshift @queue,$_; # Add to queue $#queue = 20; # Trim queue } } __END__ =head1 When you're processing large data files in Perl, you can simply 'slurp' them into a list in memory, and iterate forward and look back through that list as many times as you like. But when your data volume increases from being large to being so huge that it won't fit in memory, that's another issue. "Perl makes the difficule easy, and the impossible becomes possible" according to Larry Wall. And such is the case with looking back in huge data. In this sample program, I'm reading a potenially massive web access log file that's named on the command line, and looking for requests for quotations. I then look back a few pages to discover (and report on) web pages viewed by the same user just prior to them asking for the quote. The mechanism is to use a Perl list as a queue onto which I add (via unshift) each new .html page as I travese the whole huge web log, and which I keeped trimmed back to a threshold of 20 elements as my lookback buffer. =cut Learn about this subject
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Other Examples
This example comes from our "Handling Huge Data" training module. You'll find a description of the topic and some
other closely related examples on the "Handling Huge Data" module index page.
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