HADR_TRANSPORT_FLOW_CONTROL

Description

This wait type is only used for databases participating in an Availability Group. When an instance reaches certain thresholds (in this case the transport layer) SQL Server will accumulate this wait as well as restrict activity by enabling Availability Flow Control. This mechanism prevents the Secondary Replicas from becoming overwhelmed. Flow control is based on the number of messages. If the amount of traffic between replicas is high the suggested solutions below can assist

Resolved by

DBAs and Developers

Suggested solutions

  1. Rewrite modification DML that performs small (row-by-row) changes. Batch modifications result in less transaction log usage and messages across the network
  2. Remove unnecessary indexes, less messages and transaction log usage on modifications
  3. Scale out database design

Additional research

Monitor SQL Server AlwaysOn Availability Groups
MSDN Blog: Monitor Performance for AlwaysOn Availability Groups

See more

Consider using ApexSQL Monitor, a Windows and SQL Server monitoring tool able to track SQL Server wait types, including the individual query wait statistics

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