Hi Monks,

I have input which is 500M pairs of 32bit integers, which don't occur more than 256 times each.

I want to load them into memory, and also have an array of how many times each int is in a pair.

Now in C, to do this I only need 5GB of ram: For the pairs: 500M * 4 (32bit int) * 2 (pairs) = 4GB. For the occurances: 1G * 1 (8bit int) = 1GB.

However when I do the same thing in perl, the ram usage is more like 256 bytes per item:

my @d;
my @p;
for (my $i=0;$i<500000000;$i++)
{
   my ($p1,$p2) = getPair();
   $d[$p1] += 1;
   $d[$p2] += 1;
   push @p, [ $p1, $p2];
}

[download]

I am seeing about 1GB RAM usage per 4M input pairs, so I would need 125G of RAM!

Is there any way you can tell perl a scalar is to be a int only of a certain size?

The other idea I have is that I should not be using array, but rather a gigantic scalar, and then pack/unpack the values in/out of the scalar?

What would be the best way to approach this in perl?

Thanks!

In reply to Memory efficient way to deal with really large arrays? by sectokia

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