Dear Colleagues, I am parsing a large undirected graph, which is stored in a plain text file larger than 4GB. In this file, each line containing two nodes and their associated information. For example: 
node1 node2 weight status
23    34     -897   1
24    46     -10    0

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It is too large to fill in RAM, so I used the following code to tie it with a hash: 
use BerkeleyDB;
use MLDBM qw(BerkeleyDB::Hash Storable);
my %hash;
my @seqRelation;
$hash{'key'} = \@seqRelation;
my $dbFile = '/tmp/relation.db';
tie %hash, 'MLDBM', -Filename => $dbFile, -Flags => DB_CREATE or die $
+!;

# read into the file content
my $inFile = shift;
open(IN,"zcat $inFile | ") or die "Can not open $inFile:$!";
while(<IN>)
{
chomp;
my @fields = split "\t";
my ($seq1,$seq2,$w,$s) = @fields;
push @{$seqRelation[$seq1]}, join(',', $seq2, $w, $s);
# also store it in the other direction
push @{$seqRelation[$seq2]}, join(',', $seq1, $w, $s);
}
......

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Here I used @seqRelation to store the data, and then assign it to the hash with the only key 'key', because BerkeleyDB::Hash can only accept hash. The above code is runnable without warning. However, I am confused by the tied file size of /tmp/relation.db. When I checked it after the program finished. It is only 48K, but original file is >4GB. It is unbelievable (but maybe I am wrong because I am not familiar the mechanism of BerkeleyDB). Is this correct or normal? I expected a much larger file size for /tmp/relation.db. I have no idea why it is so small. I am worrying whether some data was missed when tying. By the way, I also need change the status values in my program. Any help or idea is appreciated. Thank you in advance! Best regards! Zhenguo

In reply to Large files tied by BerkeleyDB with MLDBM by fortunezhang

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