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Paraphrased from the old Service Broker team blog: This wait type is when a thread is waiting to access the list of buffers used to receive messages. There is one thread that adds empty buffers to the list and one thread that removes buffers for processing when they have data in.

(Books Online description: “Occurs when waiting for access to receive a message on a connection endpoint. Receive access to the endpoint is serialized.”)

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Added in SQL Server version:


Removed in SQL Server version:


Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 249 in 2008 and 2008 R2, 256 in 2012, and 263 in 2014 RTM. After 2014 RTM, you must check the DMV to get the latest value as some map_key values have changed in later builds.

Other information:

I have not seen this wait type be a noticeable contention point.

Known occurrences in SQL Server (list number matches call stack list):

  1. TBD

Abbreviated call stacks (list number matches known occurrences list):

  1. TBD