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cursor.maxTimeMS()

Definition

cursor.maxTimeMS(<time limit>)

mongo Shell Method

This page documents the mongo shell method, and does not refer to the MongoDB Node.js driver (or any other driver) method. For corresponding MongoDB driver API, refer to your specific MongoDB driver documentation instead.

Specifies a cumulative time limit in milliseconds for processing operations on a cursor.

The maxTimeMS() method has the following parameter:

Parameter Type Description
milliseconds integer Specifies a cumulative time limit in milliseconds for processing operations on the cursor.

Important

maxTimeMS() is not related to the NoCursorTimeout query flag. maxTimeMS() relates to processing time, while NoCursorTimeout relates to idle time. A cursor’s idle time does not contribute towards its processing time.

Behaviors

MongoDB targets operations for termination if the associated cursor exceeds its allotted time limit. MongoDB terminates operations that exceed their allotted time limit using the same mechanism as db.killOp(). MongoDB only terminates an operation at one of its designated interrupt points.

MongoDB does not count network latency between the client and the server towards a cursor’s time limit. For a sharded cluster, however, MongoDB does include the latency between the mongos and mongod instances towards this time limit.

Queries that generate multiple batches of results continue to return batches until the cursor exceeds its allotted time limit.

Session Idle Timeout Overrides maxTimeMS

Starting in MongoDB 3.6, MongoDB drivers and the mongo shell associate all operations with a server session, with the exception of unacknowledged write operations. For operations not explicitly associated with a session (i.e. using Mongo.startSession()), MongoDB drivers and the mongo shell creates an implicit session and associates it with the operation.

If a session is idle for longer than 30 minutes, the MongoDB server marks that session as expired and may close it at any time. When the MongoDB server closes the session, it also kills any in-progress operations and open cursors associated with the session. This includes cursors configured with noCursorTimeout or a maxTimeMS greater than 30 minutes.

For example, consider a find() operation with the maxTimeMS configured for a timeout of 31 minutes. The server returns a cursor along with a batch of documents defined by the cursor.batchSize() of the find(). The session refreshes each time the application requests a new batch of documents from the server. However, if the application takes longer than 30 minutes to process the current batch of documents, the session is marked as expired and closed. When the server closes the session, it also kills the cursor despite the cursor being configured with maxTimeMS greater than 30 minutes. When the application requests the next batch of documents, the server returns an error.

For operations that return a cursor, if the cursor may be idle for longer than 30 minutes, issue the operation within an explicit session using Session.startSession() and periodically refresh the session using the refreshSessions command. For example:

var session = db.getMongo().startSession()
var sessionId = session.getSessionId().id

var cursor = session.getDatabase("examples").getCollection("data").find().noCursorTimeout()
var refreshTimestamp = new Date() // take note of time at operation start

while (cursor.hasNext()) {

  // Check if more than 5 minutes have passed since the last refresh
  if ( (new Date()-refreshTimestamp)/1000 > 300 ) {
    print("refreshing session")
    db.adminCommand({"refreshSessions" : [sessionId]})
    refreshTimestamp = new Date()
  }

  // process cursor normally

}

In the example operation, the db.collection.find() method is associated with an explicit session. The cursor is configured with cursor.maxTimeMS() to keep the cursor open for at least 31 minutes. The while loop includes a block that uses refreshSessions to refresh the session every 5 minutes. Since the session will never exceed the 30 minute idle timeout, the cursor can remain open up to the configured maxTimeMS().

For MongoDB drivers, defer to the driver documentation for instructions and syntax for creating sessions.

Examples

Example

The following query specifies a time limit of 50 milliseconds:

db.collection.find({description: /August [0-9]+, 1969/}).maxTimeMS(50)
←   cursor.max() cursor.min()  →