#! perl -sw
use strict;

my $count = 0;
my @lines;
while( <> ) {
    $count++;
    my @f = ( split /\t/, $_, 7 )[ 0, 2, 5 ];
    push @lines, \@f;
    
    if( $count >= 300000 ) {  #size of buffer
        $count = 0;
        print_buffer( \@lines );
    }
}
print_buffer( \@lines );

sub print_buffer {
    my ($aref) = @_;
    foreach (@$aref) {
        print join( "\t", @$_ ) . "\n";
    }
    splice( @$aref );
}