32-bit limitations

32-bit MongoDB processes are limited to about 2.5 gb of data.  This has come as a surprise to a lot of people who are used to not having to worry about that.  The reason for this is that the MongoDB storage engine uses memory-mapped files for performance.

By not supporting more than 2gb on 32-bit, we%u2019ve been able to keep our code much simpler and cleaner.  This greatly reduces the number of bugs, and reduces the time that we need to release a 1.0 product. The world is moving toward all 64-bit very quickly.  Right now there aren%u2019t too many people for whom 64-bit is a problem, and in the long term, we think this will be a non-issue.

7 months ago via blog.mongodb.org

This is more recommended reading for those that are considering using MongoDB. For some, this is a deal-breaker. I don’t necessarily agree with this decision, but I do hope that 64bit support by hypervisors and VPS providers is more mature by the time Mongo matures.