[Note from Pinal]: This is a new episode of Notes from the Fields series. AlwaysOn is a very complex subject and not everyone knows many things about this. The matter of the fact is there is very little information available on this subject online and not everyone knows everything about this. This is why when a very common question related to AlwaysOn comes, people get confused.
In this episode of the Notes from the Field series database expert John Sterrett (Group Principal at Linchpin People) explains a very common issue DBAs and Developer faces in their career and is related to AlwaysOn Availability Group. Linchpin People are database coaches and wellness experts for a data driven world. Read the experience of John in his own words.
After completing several AlwaysOn Availability Group implementations there are two questions that come up frequently. When did my availability group failover? Where is my read-write replica? The answer to the first one is provided here [http://johnsterrett.com/2014/03/18/where-is-my-availability-group/ ]. Today, were going to look at the answer to the second question.
Where is my read-write replica?
The following script, when executed on an availability group replica returns the availability group name, current role state, and database name. This will let you know if this instance is hosting the PRIMARY “read/write” replica.
IF SERVERPROPERTY ('IsHadrEnabled') = 1 BEGIN
SELECT AvailabilityGroup = ag.name,
AvailabilityGroupRole = ars.role_desc,
FROM sys.databases db
INNER JOIN sys.availability_databases_cluster adc ON db.group_database_id = adc.group_database_id
INNER JOIN sys.availability_groups ag ON adc.group_id = ag.group_id
INNER JOIN sys.dm_hadr_availability_replica_states ars ON ag.group_id = ars.group_id
AND db.replica_id = ars.replica_id
SELECT NULL AS AvailabilityGroup, NULL AS AvailabilityGroupRole, name
How do I check all replicas?
Now you know how to check if an instance of SQL Server participating in an AlwaysOn Availability Group is the “Read/Write” PRIMARY role. Next, we can utilize Central Management Server to run the same script across your other instances participating as replicas in your AlwaysOn Availability Group configuration. If you have never used Central Management Server this step-by-step guide can get you going in 10 minutes.
For this week, I have an windows failover cluster with two nodes “SQL2012DR” and “SQL2012PROD1 aka localhost,1433”). Each node hosts its own default instance of SQL Server. There are two separate AlwaysOn Availability Groups. Using Central Management Server, I can rerun the query above and quickly see where my read/write replica is.
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Reference: Pinal Dave (http://blog.sqlauthority.com)