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cursor.tailable()

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  • Definition
  • Behavior
cursor.tailable()

Important

mongosh Method

This is a mongosh method. This is not the documentation for Node.js or other programming language specific driver methods.

In most cases, mongosh methods work the same way as the legacy mongo shell methods. However, some legacy methods are unavailable in mongosh.

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

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

Marks the cursor as tailable keeping it open even when the client exhausts all results.

For use against a capped collection only. Using ~cursor.tailable() against a non-capped collection returns an error.

cursor.tailable() uses the following syntax:

cursor.tailable( { awaitData : <boolean> } )

~cursor.tailable() has the following parameter:

Parameter
Type
Description
awaitData
boolean

Optional. For use with DBQuery.Option.tailable. Sets the cursor to block the query thread when no data is available and await data for a set time instead of immediately returning no data. The cursor returns no data only if the timeout expires.

By default, if maxTimeMS is set on the command that created the cursor, then the timeout for awaitData is the remaining time. Otherwise, the default timeout is 1000 milliseconds.

You can set a timeout when running getMore on a cursor with awaitData enabled.

Defaults to false.

Returns:The cursor that ~cursor.tailable() is attached to.

A tailable cursor performs a collection scan over a capped collection. It remains open even after reaching the end of the collection. Applications can continue to iterate the tailable cursor as new data is inserted into the collection.

If awaitData is true, when the cursor reaches the end of the capped collection, mongod blocks the query thread for the timeout interval and waits for new data to arrive. When new data is inserted into the capped collection, mongod signals the blocked thread to wake and return the next batch to the client.

See Tailable Cursors.

← cursor.sort()

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