db.collection.estimatedDocumentCount()¶

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Definition
Behavior
Example

Definition¶

db.collection.estimatedDocumentCount(options)¶

mongo Shell Method

This page documents the mongo shell method, and does not refer to the MongoDB Node.js driver (or any other driver) method. For corresponding MongoDB driver API, refer to your specific MongoDB driver documentation instead.

New in version 4.0.3.

Returns the count of all documents in a collection or view. The method wraps the count command.

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db.collection.estimatedDocumentCount( <options> )

Parameter	Type	Description
options	document	Optional. Extra options that affect the count behavior.

The options document can contain the following:

Field	Type	Description
`maxTimeMS`	integer	Optional. The maximum amount of time to allow the count to run.

Behavior¶

Mechanics¶

db.collection.estimatedDocumentCount() does not take a query filter and instead uses metadata to return the count for a collection.

Sharded Clusters¶

On a sharded cluster, the resulting count will not correctly filter out orphaned documents.

Unclean Shutdown¶

After an unclean shutdown, the count may be incorrect.

After an unclean shutdown of a mongod using the Wired Tiger storage engine, count statistics reported by db.collection.estimatedDocumentCount() may be inaccurate.

The amount of drift depends on the number of insert, update, or delete operations performed between the last checkpoint and the unclean shutdown. Checkpoints usually occur every 60 seconds. However, mongod instances running with non-default --syncdelay settings may have more or less frequent checkpoints.

Run validate on each collection on the mongod to restore the correct statistics after an unclean shutdown.

Client Disconnection¶

Starting in MongoDB 4.2, if the client that issued the db.collection.estimatedDocumentCount() disconnects before the operation completes, MongoDB marks the db.collection.estimatedDocumentCount() for termination (i.e. killOp on the operation).

Example¶

The following example uses db.collection.estimatedDocumentCount to retrieve the count of all documents in the orders collection:

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db.orders.estimatedDocumentCount({})