TTL Index in MongoDB

TTL Index: - Time To Live
----------
-> TTL indexes are special single-field indexes that MongoDB can use to automatically remove documents from a collection after a certain amount of time or at a specific clock time.


Create TTL:
------------
-> Ex: To create a Index which deletes the data more than 6 months.

db.eventlog.createIndex( { "lastModifiedDate": 1 }, { expireAfterSeconds: 1.577e+7 } )


collMod - to modify TTL index
------------------------------
db.runCommand( { collMod: "sessions",
                 index: { keyPattern: { lastAccess: 1 },
                          expireAfterSeconds: 3600
                        }
})

o/p:
----

{ "expireAfterSeconds_old" : 1800, "expireAfterSeconds_new" : 3600, "ok" : 1 }


To see all the Indexes in a Coll
---------------------------------
db.people.getIndexes()


To see Indexes in a entire DB
------------------------------
db.getCollectionNames().forEach(function(collection) {
   indexes = db[collection].getIndexes();
   print("Indexes for " + collection + ":");
   printjson(indexes);
});


Deleting a Index
------------------
db.pets.dropIndex( "catIdx" )
db.pets.dropIndex( { "cat" : -1 } )
db.collection.dropIndexes()