OP_QUERYwire protocol flags, such as the
tailableflag, to change the behavior of queries.
cursor.addOption()method has the following parameter:
mongo shell provides several additional cursor flags to
modify the behavior of the cursor.
Sets the cursor not to close once the last data is received, allowing the query to continue returning data added after the initial results were exhausted.
Allows querying of a replica slave.
Prevents the server from timing out idle cursors.
For use with .. data:: DBQuery.Option.tailable; sets the cursor to block and await data for a while rather than returning no data. The cursor will return no data once the timeout has expired.
Sets the cursor to return all data returned by the query at once rather than splitting the results into batches.
Sets the cursor to return partial data from a query against a sharded cluster in which some shards do not respond rather than throwing an error.
The following example adds the
DBQuery.Option.tailable flag and the
DBQuery.Option.awaitData flag to ensure that the query returns a
tailable cursor. The sequence creates a cursor that will wait for few
seconds after returning the full result set so that it can capture and
return additional data added during the query:
var t = db.myCappedCollection; var cursor = t.find().addOption(DBQuery.Option.tailable). addOption(DBQuery.Option.awaitData)
Adding incorrect wire protocol flags can cause problems and/or extra server load.