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AlwaysOn_health Extended Event Session

The AlwaysOn_health XEvent session is installed by SQL Server by default, and started by the Create Availability Group wizard when a new availability group is created.

AlwaysOn_health Extended Event Session

The xEvent session collects events triggered by events directly affecting AlwaysOn availability group like;

  • AlwaysOn errors
  • AlwaysOn state transitions
  • AlwaysOn DDL executed to create, drop, or modify the availability group

The following symptoms should lead to review of the AlwaysOn_Health data:

  • Availability group unexpectedly in the Resolving state
  • Cannot access availability databases
  • Availability group in an indeterminate state like corrupt
  • Unexpected availability group fail-over

If you script out the AlwaysOn_health extended event, you will get the below T-SQL. The AlwaysOn_health session detects significant number of errors like a dramatic shift in synchronization, state transition, ability to fail over, and many more.

CREATE EVENT SESSION [AlwaysOn_health] ON SERVER 
ADD EVENT sqlserver.alwayson_ddl_executed,
ADD EVENT sqlserver.availability_group_lease_expired,
ADD EVENT sqlserver.availability_replica_automatic_failover_validation,
ADD EVENT sqlserver.availability_replica_manager_state_change,
ADD EVENT sqlserver.availability_replica_state,
ADD EVENT sqlserver.availability_replica_state_change,
ADD EVENT sqlserver.error_reported(
    WHERE (	[error_number]=(9691) OR [error_number]=(35204) OR [error_number]=(9693) OR 
			[error_number]=(26024) OR [error_number]=(28047) OR [error_number]=(26023) OR
			[error_number]=(9692) OR [error_number]=(28034) OR [error_number]=(28036) OR 
			[error_number]=(28048) OR [error_number]=(28080) OR [error_number]=(28091) OR 
			[error_number]=(26022) OR [error_number]=(9642) OR [error_number]=(35201) OR 
			[error_number]=(35202) OR [error_number]=(35206) OR [error_number]=(35207) OR 
			[error_number]=(26069) OR [error_number]=(26070) OR [error_number]>(41047) AND 
			[error_number]<(41056) OR [error_number]=(41142) OR [error_number]=(41144) OR 
			[error_number]=(1480) OR [error_number]=(823) OR [error_number]=(824) OR 
			[error_number]=(829) OR [error_number]=(35264) OR [error_number]=(35265) OR 
			[error_number]=(41188) OR [error_number]=(41189))
		 ),
ADD EVENT sqlserver.hadr_db_partner_set_sync_state,
ADD EVENT sqlserver.lock_redo_blocked
ADD TARGET package0.event_file(SET filename=N'AlwaysOn_health.xel',max_file_size=(5),max_rollover_files=(4))
WITH (
		MAX_MEMORY=4096 KB,EVENT_RETENTION_MODE=ALLOW_SINGLE_EVENT_LOSS,MAX_DISPATCH_LATENCY=30 SECONDS,
		MAX_EVENT_SIZE=0 KB,MEMORY_PARTITION_MODE=NONE,TRACK_CAUSALITY=OFF,STARTUP_STATE=ON
	)
GO

Enjoy Learning!

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SQL Geek

Dharmendra is a SQL Server/Microsoft Data Platform professional with over eight years of experience. He enjoys helping others in the SQL Server community and does this by contributing on blogs, speaking at several SQL events. His passion and focus is to explore and share more and more on SQL Server.

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