MongoDB disk space reclamation

Question

I am familiar both with the MongoDB repairDatabase and compact commands, but these both seem to lock the database and/or collection. Is there another way to reclaim deleted disk space without essentially shutting down the database? What are best practices in this area? Thanks!

Answer 1

Best practice would probably depend on your schema and what your application does. Here's my use case, perhaps you can learn something... My application is storing very large amounts of time stamped data samples. Deleting data from a very large store is a very expensive operation, this gets more complicated when you try doing this on live systems. MongoDB had several issues in the past with reclaiming the disk space back to OS and we had to dance around this, not sure how good it works now. But what we did solved everything for good - we partitioned the data in such way so that we could dispose of old stuff by simply dumping entire database. Dropping mongodb database is a very cheap and efficient operation, almost instantaneous even when you drop a TB. Note that dropping collection is not as effective as dropping database, this was actually a key to the solution. For doing this we had to redesign the schema.. Your case of course could be different, but the lesson learned is that deleting data from large storage is very expensive.

Answer 2

The best method currently is to run a Master Slave Setup. Shutdown 1 mongod instance and let it resync.

More details here: Reducing MongoDB database file size