MongoDB Drop Collection

What is MongoDB Drop Collection?

MongoDB drop collection is used for removing views or collections from the database. All the indexes that are related to the dropped collection are also dropped by this method.

Syntax

Return Values

• When the collection is dropped successfully then it returns true.
• When a collection required to be dropped does not exist then false is returned by it.

Parameters

MongoDB drop collection takes only one optional parameter, except that no other parameters are taken by the MongoDB drop collection.

The optional parameter taken by it is called the document by which the write concern of the drop collection is represented. Users can use this parameter if the requirement is to omit the default write concern.

Uses

dp.collection.drop() method is used for the complete removal of a collection inclusive of the indexes of that collection. And the collection can be again created by the user after the removal and they can build all the indexes again.

MongoDB Drop Collection Behavior

• There is a creation of an invalidate by the db.collection.drop() method and drop command for change streams opened on dropped collection.
• After MongoDB 4.4, It is possible for the drop command and the db.collection.drop() method to abort any in-progress index builds available on the target collection even before the collection dropping. In the versions previous to MongoDB 4.4, it is not possible to drop any in-progress index builds available on the target collection as it results in the creation of an error and leads to the failure of dropping the collection.
• If the index on the primary is aborted for the shard replica sets or replica sets, then it doesn't mean that the secondary index will also abort simultaneously.

How to Reuse Dropped Collection Name as Sharded Clusters

In a sharded cluster, if the collection is created by you with the name same as the collection dropped previously then in the versions earlier to MongoDB 5.0, the operations may be forwarded by the mongos to the incorrect shard. To avoid this problem, perform operations according to the instructions given below according to the versions of MongoDB.

• No special action is needed for the sharded cluster running MongoDB version 5.0 or later versions.
• And for the sharded cluster running MongoDB version 4.4 and its prior version, if the drop() method is used by you then the same collection is created by you having a name similar to the dropped collection. Then you must do one of the following:
  • For removing existing documents and for reusing them, use the db.collection.remove().
  • Use flushRouterConfig for flushing the cached routing table on each mongos.

Resource Locking in MongoDB Drop Collection

For the operation duration, an exclusive lock is obtained by the db.collection.drop() on the collection specified in the command. All the other operations require waiting until the lock is released by the db.collection.drop().

In the versions previous to MongoDB 4.2, an exclusive lock is obtained by the db.collection.drop() on the parent database. Due to this all the operations on the Database and all the operations on all the collections of the database are blocked during the drop operation.

Examples

Drop a Collection Using Default Write Concern

The collection has the named employee in the current database dropped by the command given below:

Drop a Collection Using w: 1 Write Concern

The collection having the name employee in the current database is dropped by the command given below with the write concern 1: