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Re^6: Reading HUGE file multiple times

by Anonymous Monk
on Apr 28, 2013 at 14:16 UTC ( #1031074=note: print w/replies, xml ) Need Help??

in reply to Re^5: Reading HUGE file multiple times
in thread Reading HUGE file multiple times

Ups, replied in a wrong place.

I tried the new code and it works really fast. Problem is there is an error with tell and it's all -1. Would be nice if I could just have ENST04000413399 as and ID but it does not mater that much. From Dumper

$VAR32564 = -1; $VAR32565 = '>ENST04000413399 ';

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Re^7: Reading HUGE file multiple times
by BrowserUk (Pope) on Apr 28, 2013 at 14:42 UTC
    Problem is there is an error with tell and it's all -1.

    D'oh! I made the same mistake you did; I forgot to change ARGV for $Library. The line should read:

    $Library_Index{<$Library>} = tell($library), scalar <$Library> until e +of($Library);

    I tested the write-the-index-to-disc code with a file containing 17,000 id/record pairs with 300,000 data records (5.2GB).

    This creates the index and writes it to disc:

    #! perl -slw use strict; use Storable qw[ store ]; print time; my %idx; $idx{ <> } = tell( STDIN ), scalar <> until eof STDIN; store \%idx, '1031021.idx' or die $!; print time;

    The whole process takes a little over 3 minutes:

    C:\test> <1031021.dat 1367160156 1367160362 C:\test>dir 1031021* 28/04/2013 15:30 193 28/04/2013 15:04 5,272,940,608 1031021.dat 28/04/2013 15:46 316,385 1031021.idx 28/04/2013 15:29 374

    And this code loads that index from disk (<1 second) and the reads 1000 random records (26 seconds) using it:

    #! perl -slw use strict; use Storable qw[ retrieve ]; print time; my $idx = retrieve '1031021.idx' or die $!; print time; open DAT, '+<', '1031021.dat' or die $!; for( 1 .. 1000 ) { my( $id, $offset ) = each %$idx; seek DAT, $offset, 0; my $vid = <DAT>; die 'mismatch' unless $id eq $vid; my $data = <DAT>; } close DAT; print time;


    C:\test> 1367160624 1367160624 1367160651

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      Perfect! Works like a charm and is blazing fast comparing to initial read method. Thanks so much for your help.

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