cursor.tailable()
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Definition
cursor.tailable()
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 MongoDB driver documentation.
Marks the cursor as tailable.
For use against a capped collection only. Using
tailable()
against a non-capped collection will return an error.cursor.tailable()
uses the following syntax:cursor.tailable( { awaitData : <boolean> } ) tailable()
has the following parameter:ParameterTypeDescriptionawaitData
booleanOptional. When
true
, enablesawaitData
.awaitData
isfalse
by default.Returns: The cursor that tailable()
is attached to.
Behavior
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 set to true
, when the cursor reaches the end of
the capped collection, MongoDB blocks the query thread
for a period of time waiting for new data to arrive. When new data is inserted
into the capped collection, the blocked thread is signaled to wake up and
return the next batch to the client.