db.collection.estimatedDocumentCount()

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Definition

Behavior
Example

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Definition

db.collection.estimatedDocumentCount(options)

Important

mongo Shell Method

This page documents a mongo method. This is not the documentation for database commands or language-specific drivers, such as Node.js. To use the database command, see the count field returned by the collStats command.

For MongoDB API drivers, refer to the language-specific MongoDB driver documentation.

Returns the count of all documents in a collection or view.

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.

For a view:

There is no metadata.
The document count is calculated by executing the aggregation pipeline in the view definition.
There is no fast estimated document count.

Sharded Clusters

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

Unclean Shutdown

This section only applies to collections.

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 statistics after an unclean shutdown.

After an unclean shutdown:

validate updates the count statistic in the collStats output with the latest value.
Other statistics like the number of documents inserted or removed in the collStats output are estimates.

Client Disconnection

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

Example

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

db.orders.estimatedDocumentCount({})