cursor.tailable()

Definition定义

cursor.tailable()

Important重要

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:

• mongo shell v4.4
• mongo shell v4.2
• mongo shell v4.0

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

Marks the cursor as tailable.将游标标记为可剪裁。

For use against a capped collection only. 仅用于封顶集合。Using tailable() against a non-capped collection will return an error.对非封顶集合使用tailable()将返回错误。

cursor.tailable() uses the following syntax:使用以下语法：

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

tailable() has the following parameter:具有以下参数：

Parameter参数	Type类型	Description描述
awaitData	boolean	Optional. 可选。When true, enables awaitData.如果为true，则启用awaitData。 awaitData is false by default.默认情况下，awaitData为false。

Returns:返回：	The cursor that tailable() is attached to.tailable()附加到的游标。

Behavior行为

A tailable cursor performs a collection scan over a capped collection. 一个可剪裁的游标在一个封顶集合上执行集合扫描。It remains open even after reaching the end of the collection. 即使在集合结束后，它仍保持打开状态。Applications can continue to iterate the tailable cursor as new data is inserted into the collection.当新数据插入集合时，应用程序可以继续迭代可剪裁游标。

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. 如果awaitData设置为true，当游标到达封顶集合的末尾时，MongoDB会阻塞查询线程一段时间，等待新数据到达。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.当新数据插入到capped集合中时，阻塞的线程将被通知唤醒，并将下一批数据返回给客户端。

See Tailable Cursors.请参见可剪裁游标。