Mongodb: when to call ensureIndex?

Question

When should I call ensureIndex? Before inserting a single record, after inserting a single record, or before calling find()?

Regards,

Johnny

Answer 1

If you have a collection that have millions of records and you are building multiple compound indices with auto-indexing turned off then you MUST ensure that you are invoking ensureIndexes() much before your first find query, possibly synchronously i.e. after ensureIndexes method returns.

The mode(foreground vs background) in which indexes are build adds extra complexity. Foreground mode locks the complete db while it is building the indexes whereas background mode allows you to query the db. However background mode of index building takes extra time.

So you must make sure that indexes have been created successfully. You can use db.currentOp() to check progress of ensureIndexes() while it is still creating indexes.