AlwaysOn Availability Groups – Query to Find Latency Part 1

AlwaysOn Availability Groups latency can be a real concern. Microsoft provides a AlwaysON Dashboard to monitor and some administration of Availability Groups in SQL Server Management Studio(SSMS). Ben Snaidero as an excellent posting about the dashboard and T-SQL monitoring of AG.

The query below uses sys.dm_hadr_database_replica_states to query the current state. It can be run on the primary or secondary server. We use a readable secondary and it is nice to see how close to real-time updates. As a roll-your-own solution, you could create a SQL Agent job to monitor and send an email when certain criteria is met.

AlwaysON AG Monitor
USE master

SELECT CAST(DB_NAME(database_id)as VARCHAR(40)) database_name,
Convert(VARCHAR(20),last_commit_time,22) last_commit_time
,CAST(CAST(((DATEDIFF(s,last_commit_time,GetDate()))/3600) as varchar) + ' hour(s), '
+ CAST((DATEDIFF(s,last_commit_time,GetDate())%3600)/60 as varchar) + ' min, '
+ CAST((DATEDIFF(s,last_commit_time,GetDate())%60) as varchar) + ' sec' as VARCHAR(30)) time_behind_primary
,CONVERT(VARCHAR(20),DATEADD(mi,(redo_queue_size/redo_rate/60.0),GETDATE()),22) estimated_completion_time
,CAST((redo_queue_size/redo_rate/60.0) as decimal(10,2)) [estimated_recovery_time_minutes]
,(redo_queue_size/redo_rate) [estimated_recovery_time_seconds]
,CONVERT(VARCHAR(20),GETDATE(),22) [current_time]
FROM sys.dm_hadr_database_replica_states
WHERE last_redone_time is not null;

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