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Re^2: Working with a very large log file (parsing data out)

by jhourcle (Prior)
on Feb 20, 2013 at 20:58 UTC ( #1019847=note: print w/replies, xml ) Need Help??

in reply to Re: Working with a very large log file (parsing data out)
in thread Working with a very large log file (parsing data out)

As logs tend to be sorted already, it's likely you can avoid the sort as the only part that's likely to be a problem memory-wise

They're sorted by the time that they finish, but the time logged is when the request was made. ... so, a long running CGI or request to transfer a large file at the end of dayN might be after other lines for dayN+1

But you still don't have to sort the whole file, as you can get everything in order, then in a second pass you sum up the values that got split up

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Re^3: Working with a very large log file (parsing data out)
by mbethke (Hermit) on Feb 21, 2013 at 00:02 UTC

    True, I missed the part where he said it's an Apache log m(

    I'd try and avoid making several passes over 1.5TB in Perl though. If you just accumulate request counts in a hash keyed by date as I just added above, you don't have to.

      The second pass is against the reduced data, not the full file. This is more complex than it needs to be, so that we try to maintain the order of whatever was seen, no matter if it can sort cleanly or not. (standard data format in webserver logs is DD/Mmm/YYYY, so if we cross months, you need a custom sort function.

      cut -d\  -f4 access_log | cut -b2-12 | uniq -c | perl -e 'my(%counts,@keys);while((my($count,$key)=(<STDIN>=~m#(\d+)\s(\d\d/\w\w\w/\d{4})#))==2){push(@keys,$key) if !$counts{$key}; $counts{$key}+=$count} print "$_\t$counts{$_}\n" foreach @keys'

      Processes a 2.5M line / 330MB access log in 6.3 seconds. If it scales linearly and I'm doing my math right, that'd be 8.4 hrs for 1.5TB.

      If the file's compressed, and you pipe through gunzip -c or similar, you might get even better times, as you'll have reduced disk IO. I ran a 2.2M line / 420MB (uncompressed) / 40MB (compressed) file in 7sec (est. 7.4 hrs for 1.5TB). If you have the processors, you could also break the file into chunks, do all of the non-perl bits in parallel on each chunk, then recombine at the end ... but then you might have to actually be able to sort to get the output in the right order.

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