1.5. Tips and limitations

For all these good features, it’s worth keeping in mind a system’s trade-offs and limitations. Some limitations should be noted before building a real-world application on MongoDB and running in production. Most of these are consequences of MongoDB’s use of memory-mapped files.

First, MongoDB should usually be run on 64-bit machines. 32-bit systems are capable of addressing only 4 GB of memory. Acknowledging that typically half of this memory will be allocated by the operating system and program processes, this leaves just 2 GB of memory on which to map the data files. So if you’re running 32-bit, and if you have even a modest number of indexes defined, you’ll be strictly limited to as little as 1.5 GB of data. Most production systems will require more than this, and so a 64-bit system will be necessary.^[13]

^[13] 64-bit architectures can theoretically address up to 16 exabytes of memory, which is for all intents and purposes unlimited.