MongoDB : What is Time to Live (TTL) index

TTL or time to live indexes are special single-field indexes that MongoDB can use to automatically remove documents from a collection after a certain amount of time. Data expiration is useful for certain types of information like machine generated event data, logs, and session information that only need to persist in a database for a finite amount of time.

To create a TTL index, use the db.collection.createIndex() method with theexpireAfterSeconds option on a field whose value is either a date or an array that contains date values.

For example, to create a TTL index on the lastModifiedDate field of the eventlog collection, use the following operation in the mongo shell:

db.eventlog.createIndex( { "lastModifiedDate": 1 }, { expireAfterSeconds: 3600 } )

Warning: The TTL index does not guarantee that expired data will be deleted immediately. 
There may be a delay between the time a document expires and the time that MongoDB removes the document from the database.



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