In mongodb is there a performance reason to separate collections into more than on database?

Question

I have an application using a MongoDB database and am about to add custom analytics. Is there a reason to use a separate database for the analytics or am I better off to build it in the application database?

Answer 1

Here are the reasons I can think of:

• Name collisions between production collections and analytics collections
• You need a different replica set configuration for analytics
• You need a different sharding configuration for analytics
• You want different physical media for some data (production data on fast disks, analytics on slow disk, for example)
• Starting in Mongo 2.2, the "global write lock" will be a per-database lock, so different databases will isolate analytics traffic from production traffic a bit more.

Unless something on this list applies to you, then you don't need to split them out. Also, it's much easier to move a collection across DBs in MongoDB than an RDBMS (as you don't have foreign keys to cause trouble), so IMO it's a relatively easy decision to delay.