Alwayon Leasetimeout

Question

Hi Experts,

Have some question related to Lease timeout behaviour in AG.

2020-12-28 02:14:39.540 Server Error: 19419, Severity: 16, State: 1.
2020-12-28 02:14:39.540 Server Windows Server Failover Cluster did not receive a process event signal from SQL Server hosting availability group 'SalesdwAG02' within the lease timeout period.
2020-12-28 02:14:39.550 Server Error: 19407, Severity: 16, State: 1.
2020-12-28 02:14:39.550 Server The lease between availability group 'SalesdwAG02' and the Windows Server Failover Cluster has expired. A connectivity issue occurred between the instance of SQL Server and the Windows Server Failover Cluster. To determine whether the availability group i
2020-12-28 02:14:39.550 Server Always On: The local replica of availability group 'SalesdwAG02' is going offline because either the lease expired or lease renewal failed. This is an informational message only. No user action is required.
2020-12-28 02:14:39.550 Server The state of the local availability replica in availability group 'SalesdwAG02' has changed from 'PRIMARY_NORMAL' to 'RESOLVING_NORMAL'. The state changed because the lease between the local availability replica and Windows Server Failover Clustering (WS

Questions

1. Why and when Lease timeout happens?
2. What value to be set for Lease timeout to start of with?
3. When Lease timeout happended, we expected a Automatic failover to happen, but it didn't happen why? Any reason for this behaviour. We have configure AG with "Synchronous commit" , "Automatic failover".
4. After changing the LeaseTimeout in windows failover cluster, do we need restart the nodes involved in AG to take into effect?
5. In SSMS, If we go to AG properties , we have setting called "Session timeout" default is 10 seconds. Any recommendations of what value to be set?

Env:
SQL Server 2017 Enterprise Edition
Windows server 2019 datacenter

Regards,
Sam

Answer 1

Hi @Sam ,

> Why and when Lease timeout happens?

You need to check you SQL server error log and cluster log to find the reason and the time that this happened.

> What value to be set for Lease timeout to start of with?

You can set the values to 20000 milliseconds. The maximum value is 100,000 ms.

> After changing the LeaseTimeout in windows failover cluster, do we need restart the nodes involved in AG to take into effect?

No, you do not need to restart the nodes. Click the Apply tap to take it effect as below screenshot.

Please refer to MS document How It Works: SQL Server AlwaysOn Lease Timeout and Diagnose Unexpected Failover or Availability Group in RESOLVING State to get more information.

> In SSMS, If we go to AG properties , we have setting called "Session timeout" default is 10 seconds. Any recommendations of what value to be set?

We recommend that you keep the time-out period at 10 seconds or greater. Refer to MS document Modify the session-timeout period for an availability group replica to get more information.

Best regards,
Cathy

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Answer 2

For more information, please see:

https://techcommunity.microsoft.com/t5/sql-server-support/how-it-works-sql-server-alwayson-lease-timeout/ba-p/317268

Answer 3

I have seen this scenario in my environment, and it was caused due to I/O issues on storage. It usually occurs while running maintenance jobs for large databases. It was resolved once we upgraded the storage to a higher performance one.
As far as Automatic failover scenario is concerned, it is advised to have a Witness disk or file share (Cloud witness in case of Azure VM's) for quorum configuration, which can help to perform Automatic failover if communication between always-on nodes is lost.

Also, please don't forget to change the lease-timeout values as recommended. :-)