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An AlwaysOn Bug with Service Broker Transmission Queue

By Paul Brewer,

An issue exists in SQL Server 2012 SP1 CU6 Availability Group Primary databases involved in Service Broker conversations. If you reused conversations and failover mode is set to manual, depending on how SQL Server had been shutdown previously, the transmission queue starts growing. Messages are sent, received by the target which sends acknowledges but where before these acknowledged messages would disappear from sys.transmission_queue, now they remain and build up. The transmission status shows nothing indicating the message has not been sent but it has. Service Broker makes no attempt to re-transmit them which is a blessing but they accumulate in the transmission queue.

The Cause

The problem occurs when the following events happen to the Availability Group Primary / Service Broker database:

  • The SQL Service is stopped / restarted, even cleanly using the configuration manager.
  • The owning clustered SQL service node is rebooted.
  • The clustered service is moved to another node using the Failover Cluster Manager in Windows or using PowerShell.
  • Any event that causes a restart of the SQL Service if there is an Availability Group Primary / Service Broker database with failover mode = manual

The Service Broker class responsible for clearing the transmission queue is not being invoked.

To fix for the problem

Here is the short list of items that need to be undertaken to solve the issue:

  • Take the database out of the availability group on the primary.
  • End all connections to the database , single user mode.
  • Disable then re-enable the Service Broker option in the database.
  • Add the database back to the Availability Group, reinitialize any standby servers.

The Problem Definition

Taking down applications that reference the database and the re-initialization of all secondary servers is the problem. When the database is out of the availability group (AG), it is unavailable for applications that connect using the AG Listener IP address. Secondary copies of the AG database are unavailable until re-initialized and synchronizing, disaster recovery and asynchronous reporting data may be unavailable for a while.

Problem Reproduction

The reproduction below is in a virtual lab environment, it uses scripts freely available on msdn to build a test environment with an Availability Group Database as part of a Service Broker dialog.

The lab environment

The SQL Service Active Directory Account is a member of the System Administrator role in SQL Server on all instances. Each of the SQL Servers has a local share C:\Share

  • PBVAD – Domain controller, Windows Server 2012 R2
  • PBV001 – SQL Server 2012 SP1 CU6 – Default instance, Service Broker Target
  • PBV002 & PBV003 – SQL Server 2012 SP1 CU6 – Default instances, Service Broker Initiators. The servers are part of a windows cluster with a file share witness.

Here is the code:

01 – Setup The Service Broker Target – PBV001

------------------------------------------
--Creating the Target Database--
------------------------------------------

--Create a Service Broker endpoint
USE master;
GO

IF EXISTS (SELECT * FROM  master.sys.endpoints WHERE name  = N'InstTargetEndpoint')
     DROP ENDPOINT  InstTargetEndpoint;
GO

CREATE ENDPOINT InstTargetEndpoint
STATE = STARTED
AS TCP (  LISTENER_PORT = 4022  )
FOR SERVICE_BROKER (AUTHENTICATION = WINDOWS  );
GO

--Create the target database, master key, and user
IF EXISTS (SELECT * FROM  sys.databases WHERE name  = N'TargetDB')
     DROP DATABASE  TargetDB;
GO

CREATE DATABASE TargetDB;
GO

USE TargetDB;
GO

CREATE MASTER KEY
ENCRYPTION BY  PASSWORD = N'<EnterStrongPassword1Here>';
GO

CREATE USER TargetUser  WITHOUT LOGIN;
GO

--Create the target certificate & backup the certificate
CREATE CERTIFICATE InstTargetCertificate
AUTHORIZATION TargetUser
WITH SUBJECT  = 'Target Certificate',
EXPIRY_DATE =  N'12/31/3010';
GO

BACKUP CERTIFICATE InstTargetCertificate
TO FILE  = N'C:\Share\InstTargetCertificate_Node3.cer';
GO

--Create message type for request and reply
CREATE MESSAGE TYPE  [//RequestMsg]
GO

CREATE MESSAGE TYPE  [//ReplyMsg]
GO

--Create a contract for the above created message
CREATE CONTRACT [//SampleContract]
(
[//RequestMsg] SENT BY  INITIATOR,
[//ReplyMsg] SENT BY  TARGET
)

--Create Queue & Service for target
USE TargetDB;
GO

CREATE QUEUE TargetQueue_TargetDB;
GO

CREATE SERVICE [//TargetService]
AUTHORIZATION TargetUser
ON QUEUE TargetQueue_TargetDB([//SampleContract]);
GO

Once complete, copy the target certificate in C:\Share to the corresponding folder on server PBV002

02 – Setup Service Broker Initiator – PBV002 (PBV003 setup later during create of AG)

---------------------------------------------
--Creating the Initiator Database--
--------------------------------------------

--Create a Service Broker endpoint
USE master;
GO

IF EXISTS (SELECT * FROM  sys.endpoints
           WHERE name  = N'InstInitiatorEndpoint')
     DROP ENDPOINT  InstInitiatorEndpoint;
GO

CREATE ENDPOINT InstInitiatorEndpoint
STATE = STARTED
AS TCP (  LISTENER_PORT = 4022  )
FOR SERVICE_BROKER (AUTHENTICATION = WINDOWS  );
GO

--Create the initiator database, master key, and user
IF EXISTS (SELECT * FROM  sys.databases
           WHERE name  = N'InitiatorDB')
     DROP DATABASE  InitiatorDB;
GO

CREATE DATABASE InitiatorDB;
GO

USE InitiatorDB;
GO

CREATE MASTER KEY
ENCRYPTION BY  PASSWORD = N'';
GO

CREATE USER InitiatorUser WITHOUT LOGIN;
GO

--Create the initiator certificate
CREATE CERTIFICATE InstInitiatorCertificate
AUTHORIZATION InitiatorUser
WITH SUBJECT  = N'Initiator Certificate',
EXPIRY_DATE =  N'12/31/3010';

BACKUP CERTIFICATE InstInitiatorCertificate
TO FILE  = N'C:\Share\InstInitiatorCertificate_Node1.cer';
GO

CREATE MESSAGE TYPE  [//RequestMsg]
GO

CREATE MESSAGE TYPE  [//ReplyMsg]
GO

--Create a contract for the above created message
CREATE CONTRACT [//SampleContract]
(
[//RequestMsg] SENT BY  INITIATOR,
[//ReplyMsg] SENT BY  TARGET
)

--Create the initiator queue and service
CREATE QUEUE InitiatorQueue_InitiatorDB;

CREATE SERVICE [//InitiatorService]
AUTHORIZATION InitiatorUser
ON QUEUE  InitiatorQueue_InitiatorDB;
GO

--Create references to target objects
CREATE USER TargetUser  WITHOUT LOGIN;

CREATE CERTIFICATE InstTargetCertificate
AUTHORIZATION TargetUser
FROM FILE  = N'C:\Share\InstTargetCertificate_Node3.cer'
GO

--Create routes
DECLARE @Cmd NVARCHAR(4000);
SET @Cmd =  N'USE InitiatorDB;
CREATE ROUTE Instiator_TO_Target_Route
WITH SERVICE_NAME =N''//TargetService'',
ADDRESS = N''TCP://PBV001:4022'';';

EXEC (@Cmd);

SET @Cmd =  N'USE msdb
CREATE ROUTE Inst_Local_InitiatorRoute
WITH SERVICE_NAME = N''//InitiatorService'',
ADDRESS = N''LOCAL''';

EXEC (@Cmd);
GO

CREATE REMOTE SERVICE  BINDING TargetBinding
TO SERVICE N'//TargetService'
WITH USER  = TargetUser;
GO

Once complete, copy the new initiator certificate from C:\Share on PBV002 to the corresponding folder on PBV001

003 – Complete Target Server Setup – PBV001

-------------------------------------------------------
--Complete the Target Conversation Objects
-------------------------------------------------------

--Create references to initiator objects
USE TargetDB
GO

CREATE USER InitiatorUser WITHOUT LOGIN;

CREATE CERTIFICATE InstInitiatorCertificate
AUTHORIZATION InitiatorUser
FROM FILE  = N'C:\Share\InstInitiatorCertificate_Node1.cer';
GO

--Create routes
DECLARE @Cmd NVARCHAR(4000);

SET @Cmd =  N'USE TargetDB;
CREATE ROUTE Target_To_Initiator_Route
WITH SERVICE_NAME = N''//InitiatorService'',
ADDRESS = N''TCP://PBV002:4022'';';

EXEC (@Cmd);

SET @Cmd =  N'USE msdb
CREATE ROUTE Inst_Local_TargetRoute
WITH SERVICE_NAME = N''//TargetService'',
ADDRESS = N''LOCAL''';

EXEC (@Cmd);

GO

GRANT SEND
ON SERVICE::[//TargetService]
TO InitiatorUser;

GO

CREATE REMOTE SERVICE  BINDING InitiatorBinding
TO SERVICE  N'//InitiatorService'
WITH USER  = InitiatorUser;

GO

04 – Send Message from Initiator – PBV002

--------------------------------------------------
--Beginning Conversation, send test message --
--------------------------------------------------

USE InitiatorDB;
GO

DECLARE @InitDlgHandle UNIQUEIDENTIFIER;
DECLARE @RequestMsg NVARCHAR(100);

BEGIN TRANSACTION;

BEGIN DIALOG @InitDlgHandle
     FROM SERVICE  [//InitiatorService]
     TO SERVICE  N'//TargetService'
     ON CONTRACT  [//SampleContract]WITH  ENCRYPTION = Off;

SELECT @RequestMsg =  N'<RequestMsg:2>Message for Target service.</RequestMsg:2>';

SEND ON CONVERSATION  @InitDlgHandle
     MESSAGE TYPE  [//RequestMsg]
     (@RequestMsg);

SELECT @RequestMsg AS  SentRequestMsg;

COMMIT TRANSACTION;

GO

At this point you should be able to send a message from the initiator to the target. The target receives the message, acknowledges it and it is removed from the initiator transmission queue.

Next perform the following actions to create an Availability Group and add the InitiatorDB to it.

  • Backup the InitiatorDB on PBV002, restore WITH NORECOVERY to PBV003.
  • Create an Availability Group with a Listener and add the InitiatorDB on PBV002 & PBV003, synchronous, manual failover.
  • Change the TargetDB Service Broker route to point to the Availability Group Listener name of the Initiator.
  • Send a test message. Again message is sent, received by target, acknowledged and removed from initiator transmission queue.

Now, restart the SQL Service of the Availability Group Primary/Service Broker Initiator using the configuration manager. Service Broker Messages are still sent, received and acknowledged but they are no longer removed from the initiator transmission queue. If you are sending a lot of messages and reusing conversations then this is a serious problem that needs to be fixed quickly and involves downtime

Conclusion

An update that enabled you to stop and restart the SQLAG primary service using the SQL configuration manager, without the issue occurring, is needed. If you could do this without breaking service broker and having to reinitialize all AG standby’s after, it would be a big step forward.

Ideally a fix is needed for crash recovery scenario’s too where logs are rolling forward/back. Just the restarting of the service is enough to trigger the issue at the moment.

Since writing this article I found a post about the same issue - http://www.sqldiablo.com/2012/04/15/service-broker-alwayson-availability-groups-odd-transmission-queue-behavior/

He doesn't state the problem is specific to manual failover mode which it is now. It mentions a fix was pending but it hasn't materialized yet as of SQL Server 2012 SP1 CU6.

UPDATE 2013/12/23 - A FIX WILL BE INCLUDED IN SQL SERVER 2012 SP1 CU 9 DUE MARCH 2014

Total article views: 2605 | Views in the last 30 days: 13
 
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