Existance of a circular reference can cause this problem. i.e. even if you undef $self->{dbo}, there exist some reference to same object. So its not removed from memory.

Here is a very simple problematic case for circular reference.

    foreach (1..5) {  
        my $a;  
        my $b;  
        $a->{b} = $b;  
        $b->{a} = $a;  
    } # since both are pointing to each other they will never get coll
+ected.
[download]

Please check your code for any circular reference.

you may try disconnecting the database handle just before you undef the $self->{dbo} as an immediate fix.

Cheers !

--VC

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your side, my side and the right side.