Fast datetimes in MongoDB
One of the most common complaints about the Perl MongoDB driver is that it tries to be a little too clever. In the current production release of MongoDB.pm (version 0.46.2 as of this writing), all datetime values retrieved by a query are automatically instantiated as DateTime objects.
The next release of MongoDB.pm will fix this problem, allowing for nearly tenfold speed increases under some circumstances. The details are available on my blog here: Fast datetimes In MongoDB.