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Fast datetimes in MongoDB

Oct 1 • Posted 1 year ago

This was originally posted to Mike Friedman’s blog. Mike is a Perl Evangelist at 10gen, working on the Perl Driver for 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 (version 0.46.2 as of this writing), all datetime values retrieved by a query are automatically instantiated as DateTime objects. DateTime is a remarkable CPAN distribution. In fact, I would say that DateTime and its related distributions on CPAN comprise one of the best date and time manipulation libraries in any programming language. But that power comes with a cost. The DateTime codebase is large, and instantiating DateTime objects is expensive. The constructor performs a great deal of validation, and creates a large amouunt of metadata which is stored inside the object. Upcoming changes to the Perl MongoDB driver solve this problem. Read more below. If you need to perform a series of complex arithmetic operations with dates, then the cost of DateTime is justified. But frequently, all you want is a simple read-only value that is sufficient for displaying to a user or saving elsewhere. If you are running queries involving a large number of documents, the automatic instantiation of thousands of complex objects becomes barrier to performance.

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