AlwaysOn Wait Types

 

When trouble-shooting AlwaysOn latency, wait statistics can be monitored for accumulation using the AlwaysOn-specific wait types in the dynamic management view (DMV) sys.dm_os_wait_stats (Transact-SQL).

For general information on using wait statistics, see SQL Server 2005 Waits and Queues. That document was written for SQL Server 2005, but its information can be applied to later SQL Server versions.

Use the T-SQL query below to retrieve all wait statistics with the AlwaysOn wait types:

SELECT * FROM sys.dm_os_wait_stats   
WHERE wait_type LIKE '%hadr%'  
ORDER BY wait_time_ms DESC  

To monitor the wait statistics by capturing extended events, use the following T-SQL command.

CREATE EVENT SESSION [alwayson] ON SERVER   
ADD EVENT sqlos.wait_info(  
    WHERE ([wait_type]=(758) OR [wait_type]=(776) OR [wait_type]=(853) OR [wait_type]=(833)))  
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=OFF)  
GO  

You can view the key-value mapping of the wait type by running the following query:

SELECT * FROM sys.dm_xe_map_values   
WHERE name='wait_types' AND map_value LIKE '%hadr%'   
ORDER BY map_key ASC  

Types of Waits

Show: