We are working on a project that may require up to 10000 databases. We are looking at MongoDB as an option but not sure if we can create that much databases.
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There is no hardcoded limit on the number of databases one can create in MongoDB. However, there are other limitations that one needs to be mindful of while creating a database. For example, there is a database limit of 100 if you are planning on using Atlas (M0, M2/M5 tier clusters). You also need to be mindful of your resources like RAM, Memory utilizations, etc.
You can read more on the Documented limits & thresholds in the MongoDB Limits and Thresholds page.
There is also a similar conversation that you might find useful:
Thank you for such an insightful reply. I just want to confirm, if I want to create 10000 databases and I don’t have any prior resource planning for the same. Then what will be the required resources and suggested tier so that I can efficiently create and manage that much databases in MongoDB.
Unfortunately there is no single easy way to answer this other than simulating the workload you’re expecting on the hardware that you think should be able to serve the workload, and checking if it can be done. Different cases could arrive at entirely different answer to this, so I would encourage you to do your own testing.