Application starts throwing SQL error after database failover.

Question

Application starts throwing SQL error after database failover.

BoobyB

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February 22, 2018 at 1:45 pm

#336327

I have a situation and looking for some guidance. I have a two node SQL server always on on setup for a HA solution. the database is setup for automatic fail-over and listener is setup as well.
Recently we had a network issue and the database failed over to the secondary node, which became the primary. From my end every thing seems to be fine.
The databases were available on node B now. I was able to query. use the listener name to connect using SSMS. However, as soon as after the fail-over, the application stop and a pop up error shows saying "SQL error". In the logs of node B I don't see any errors but I also don't see any request coming to Node B either. It's like the application is not sending any request to node B. As soon as I fail-over back to node A, the application starts working instantaneously. This what I have tried so Far
- Asked the application team to make sure the connection or what ever configuration they r using to point to the database, use it with the listener name only. I have scripted out the logins from server A with original SIDs and implemented on server B. I don't see any login failed error in the sql logs when server B is the primary so I don't think it's the login issue but lets see.
Both of the SQL server nodes are within same sub-net. The listener IP is using just one subnet.
Hope you guys can help.
Regards,
Bobby

SQL Server]Unable to access availability database'XXXX' because the database replica is not in the PRIMARY or SECONDARY role.

Connections to an availability database is permitted only when the database replica.......

I understand this to appear when the network issue was happening, or the DB is in the process of moving from primary to secondary node. However, once the fail-over is complete this should disappear.

Ivan R. SSChasing Mays Points: 628 More actions · Answer 1

hello Bobby -- have you considered logging in from the problematic app host and trying a ping, then a simple sqlcmd login just to check if it would go though? usually the error thrown would be indicative of the issue.

a few ideas that come to mind that might help would be: check the connection string of the app; check if you have a DNS alias issue, a typo, incorrect connection string params, try the same test from a different host or a host that is known to work.

I would personally try different ways of connecting to the replica to try to get an error message and narrow down the issue.

hope this helps
ivan

BoobyB SSCertifiable Points: 5470 More actions · Answer 2

Hello.

I haven't had a chance to actually try and work with on the application server. However, just yesterday application guys send a snap-shot of the logs they say appears in their logs when issue happens.

Steve Jones - SSC Editor SSC Guru Points: 734418 More actions · Answer 3

This appears after failover is complete? I would double check all the configuration and make sure every database you expect is in the AG. Make sure the database is not in recovery.

BoobyB SSCertifiable Points: 5470 More actions · Answer 4

Hi, Thanks for the response.

Yes, I checked it, once the fail over is complete, all the databases are up sync and available.

Regards

Ivan R. SSChasing Mays Points: 628 More actions · Answer 5

hello -- you might already be aware that the driver they use will have an impact?
But just in case here's the link: https://docs.microsoft.com/en-us/sql/database-engine/availability-groups/windows/always-on-client-connectivity-sql-server

e.g.

Driver	Multi-Subnet Failover	Application Intent	Read-Only Routing	Multi-Subnet Failover: Faster Single Subnet Endpoint Failover	Multi-Subnet Failover: Named Instance Resolution For SQL Clustered Instances
SQL Native Client 11.0 ODBC	Yes	Yes	Yes	Yes	Yes
SQL Native Client 11.0 OLEDB	No	Yes	Yes	No	No
ADO.NET with .NET Framework 4.0 with connectivity patch*	Yes	Yes	Yes	Yes	Yes
ADO.NET with .NET Framework 3.5 SP1 with connectivity patch**	Yes	Yes	Yes	Yes	Yes
Microsoft JDBC driver 4.0 for SQL Server

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 6

Check that the app is connecting to the listener, not to the server directly.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

andrew gothard SSChampion Points: 12301 More actions · Answer 7

qur7 - Thursday, February 22, 2018 1:45 PM
I have a situation and looking for some guidance. I have a two node SQL server always on on setup for a HA solution. the database is setup for automatic fail-over and listener is setup as well.
Recently we had a network issue and the database failed over to the secondary node, which became the primary. From my end every thing seems to be fine.
The databases were available on node B now. I was able to query. use the listener name to connect using SSMS. However, as soon as after the fail-over, the application stop and a pop up error shows saying "SQL error". In the logs of node B I don't see any errors but I also don't see any request coming to Node B either. It's like the application is not sending any request to node B. As soon as I fail-over back to node A, the application starts working instantaneously. This what I have tried so Far
- Asked the application team to make sure the connection or what ever configuration they r using to point to the database, use it with the listener name only. I have scripted out the logins from server A with original SIDs and implemented on server B. I don't see any login failed error in the sql logs when server B is the primary so I don't think it's the login issue but lets see.
Both of the SQL server nodes are within same sub-net. The listener IP is using just one subnet.
Hope you guys can help.
Regards,
Bobby

Hi,
if, as I suspect, the nodes are on different subnets, to get automatic failover you need to ensure that your connection string has the MULTISUBNETFAILOVER=TRUE option is set, and that the driver, and if applicable .NET framework version supports it. If not, then either you have to repoint manually, or it's not going to resolve until after your next DNS refresh

I'm a DBA.
I'm not paid to solve problems. I'm paid to prevent them.

BoobyB SSCertifiable Points: 5470 More actions · Answer 8

Thanks for the feedback.

the two nodes are in the same subnet. I was aware about the different sub-net issue however didn't think it applied in my case.
we resolved the issue. one of the configuration from the application side was using node A server name instead of listener name. once this was corrected, it all worked.
Thanks for the help.

Regards,

Ivan R. SSChasing Mays Points: 628 More actions · Answer 9

qur7 - Tuesday, February 27, 2018 7:06 AM
Thanks for the feedback.
the two nodes are in the same subnet. I was aware about the different sub-net issue however didn't think it applied in my case.
we resolved the issue. one of the configuration from the application side was using node A server name instead of listener name. once this was corrected, it all worked.
Thanks for the help.
Regards,

good to know. checking the connection string was part of my earlier suggestion. 🙂