Finding Transaction latency in an Always on Synchronous replica

1) Execute below query on your Always on Primary replica,


-- Create required objects to collect the data
use [Tempdb]
GO
IF OBJECT_ID('Perfcounters') IS NOT NULL
DROP TABLE Perfcounters
GO
CREATE TABLE Perfcounters
(CapturedTime DATETIME NOT NULL,
[Transaction Delay] BIGINT, [Mirrored Write Transactions/sec] BIGINT
)
GO

ALTER TABLE [dbo].Perfcounters
ADD [Transaction Delay in MS]
AS (convert(decimal(5,2),[Transaction Delay]*1.0/[Mirrored Write Transactions/sec]*1.0))
PERSISTED NOT NULL

2) Below query can be executed in a query window or as a SQL Server agent job in primary replica. Remember to change “Instance_Name=’Alwayson Database Name'” to appropriate Alwayson database name before executing the query,


use [Tempdb]
GO
set nocount on
while (1=1)
begin
insert into Perfcounters
SELECT CURRENT_TIMESTAMP as Time
,pt.* FROM(SELECT RTRIM(object_name) + ' : ' + counter_name CounterName
, cntr_value from sys.dm_os_performance_counters
where Instance_Name='Alwayson Database Name' and counter_name in ('Transaction Delay','Mirrored Write Transactions/sec')) as SourceData
PIVOT
(SUM(cntr_value)
FOR CounterName
IN ([SQLServer:Database Replica : Transaction Delay],[SQLServer:Database Replica : Mirrored Write Transactions/sec])
) pt
waitfor delay '00:00:03'  -- Change this as per your requirement for collection
End

3) While the above query is getting executed from your query window or SQL Server agent job, you can execute the below query to get the latency values,


use [Tempdb]
GO
select * from Perfcounters order by CapturedTime desc

4) Remember to stop the query running as part of step 2 in this article on query window or as a SQL Agent job when not required.

Thank You,
Vivek Janakiraman

Disclaimer:
The views expressed on this blog are mine alone and do not reflect the views of my company or anyone else. All postings on this blog are provided “AS IS” with no warranties, and confers no rights.

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Listener entry in sys.availability_group_listeners exists even after related Availability group is deleted

Environment

Alwayson_Visio.JPG

-> A request comes in to drop the existing Always-on availability group JBDB from above environment.

-> Alwayson Availability group should be deleted/dropped by connecting to Primary Replica JBAG1 using SQL Server Management Studio.

-> But, someone tried deleting the Availability group from SQL Server management studio connected using the LISTENER JBAPP and got below error,

TITLE: Microsoft SQL Server Management Studio
——————————
Drop failed for Availability Group ‘JBDB’. (Microsoft.SqlServer.Management.SDK.TaskForms)
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=14.0.17224.0+((SSMS_Rel_17_4).180212-1043)&EvtSrc=Microsoft.SqlServer.Management.Smo.ExceptionTemplates.FailedOperationExceptionText&EvtID=Drop+AvailabilityGroup&LinkId=20476
——————————
ADDITIONAL INFORMATION:
An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo)
——————————
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 – Could not open a connection to SQL Server) (Microsoft SQL Server, Error: 53)
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft%20SQL%20Server&EvtSrc=MSSQLServer&EvtID=53&LinkId=20476
——————————
The network path was not found
——————————
BUTTONS:
OK
——————————

Blog50_1.JPG

-> When “Always On High Availability” folder for SQL Server Instance JBAG1 which is the primary is refreshed from SQL Server management studio, “Availability group” JBDB is not available.

-> But you will see Availability group JBDB “Resolving” at the secondary replica “JBAG2”. At this point you delete the Availability group JBDB from your secondary replica JBAG2 from SSMS.

-> When connected to cluster administrator (cluadmin.msc), you will not see roles related to Availability group JBDB visible.

-> Lets try creating another Availability group with same name JBDB that contains listener JBAPP. It fails with below error,

TITLE: Microsoft SQL Server Management Studio
——————————
Create failed for Availability Group ‘JBDB’. (Microsoft.SqlServer.Management.HadrModel)
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=14.0.17224.0+((SSMS_Rel_17_4).180212-1043)&EvtSrc=Microsoft.SqlServer.Management.Smo.ExceptionTemplates.FailedOperationExceptionText&EvtID=Create+AvailabilityGroup&LinkId=20476
——————————
ADDITIONAL INFORMATION:
An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo)
——————————
Failed to create availability group ‘JBDB’, because a Windows Server Failover Cluster (WSFC) group with the specified name already exists. The operation has been rolled back successfully. To retry creating an availability group, either remove or rename the existing WSFC group, or retry the operation specifying a different availability group name. (Microsoft SQL Server, Error: 41171)
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft%20SQL%20Server&ProdVer=14.00.1000&EvtSrc=MSSQLServer&EvtID=41171&LinkId=20476
——————————
BUTTONS:
OK
——————————

Blog50_2.JPG

-> The error advises us that the ROLE JBDB is already exists in cluster administrator. But we have checked it and it is not present.

-> Execute below query on JBAG1 which was acting as the primary replica when Availability group JBDB was deleted from SSMS using Listener name,


select * from sys.availability_group_listeners
go
select * from sys.availability_groups

Blog50_3.JPG

-> You see an orphaned listener entry under system table sys.availability_group_listeners. But no corresponding entries in sys.availability_groups.

-> Lets first try restarting the SQL Services on JBAG1 and then try running the below queries,

 

select * from sys.availability_group_listeners
go
select * from sys.availability_groups 

-> The orphaned entry is no longer present in sys.availability_group_listeners after the SQL Server restart.

-> Lets try creating Availability group with same name JBDB that contains listener JBAPP and it works fine this time.

Thank You,
Vivek Janakiraman

Disclaimer:
The views expressed on this blog are mine alone and do not reflect the views of my company or anyone else. All postings on this blog are provided “AS IS” with no warranties, and confers no rights.

Always ON Availability group automatic failover to a particular node

Environment

Blog25_1

-> One of my client had an Alwayson setup as depicted above. They advised me that all their Availability group should reside only on server JBSERVER1.JB.NET which is in Primary datacentre. Even if it fails over to server JBSERVER2.JB.NET in secondary datacentre, it should be immediately failed back to server JBSERVER1.JB.NET and they are not worried about the downtime during the fail back.

-> I felt it to be a strange requirement and requested them for reason. They advised me that Server JBSERVER1.JB.NET hosts SSD drives which performs many times better than the SAS drives hosted on server JBSERVER2.JB.NET.

-> I configured a SQL Server agent job to execute below query and that took care of my Client’s requirement.


DECLARE @ServerName NVARCHAR(256)  = @@SERVERNAME
DECLARE @RoleDesc NVARCHAR(60)

SELECT @RoleDesc = a.role_desc
    FROM sys.dm_hadr_availability_replica_states AS a
    JOIN sys.availability_replicas AS b
        ON b.replica_id = a.replica_id
WHERE b.replica_server_name = @ServerName
IF @RoleDesc = 'SECONDARY'
BEGIN
    ALTER AVAILABILITY GROUP [JBAG] FAILOVER;
END

Thank You,
Vivek Janakiraman

Disclaimer:
The views expressed on this blog are mine alone and do not reflect the views of my company or anyone else. All postings on this blog are provided “AS IS” with no warranties, and confers no rights.