db.collection.estimatedDocumentCount()¶

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Definition
Behavior
Example

Definition¶

db.collection.estimatedDocumentCount(options)¶

Important

mongosh Method

This page documents a mongosh method. This is not the documentation for a language-specific driver such as Node.js.

For MongoDB API drivers, refer to the language-specific :driver:`MongoDB driver documentation </>`.

For the legacy mongo shell documentation, refer to the documentation for the corresponding MongoDB Server release:

:v4.4:`mongo shell v4.4 </mongo>`
mongo shell v4.2

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.

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:

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db.orders.estimatedDocumentCount({})