About a day ago while working on a client system I have noticed a message that reads Error: 19432, Severity: 16, State: 0. This message appeared on the system that runs SQL Server 2016 and has Always On Configured on it. The message itself is very clear to understand and that it also says No user action is required but Fixing Always On Error:19432, Severity: 16, State: 0 is a comparatively easy job. Let’s see how the error message looks like in Error log.
Always On Availability Groups transport has detected a missing log block for availability database "AdvancedDB". LSN of last applied log block is (54519:12104:0). Log scan will be restarted to fix the issue. This is an informational message only. No user action is required.
[WARNING] 2017-09-30 20:22:04.81 spid435s Always On Availability Groups connection with primary database established for secondary database 'AdvancedDB' on the availability replica 'SSCSQL013' with Replica ID: {99c0cbd8-d08a-4cb4-b20f-2eb186a5be3d}. This is an informational message only. No user action is required.
[WARNING] 2017-09-30 20:22:04.82 spid435s The recovery LSN (54519:12120:1) was identified for the database with ID 44. This is an informational message only. No user action is required.
Basically what is happening here is, while sending the data to a replica apparently, it is experiencing slow throughput and one will notice HADR_Sync_Commit wait types for the replica. Also, one will notice that intermittent issue with the size of REDO log is increasing. These can happen with multiple databases and can occur randomly. MS recommends applying the latest service pack to your Always on Group. Just in case, if needed here is the document that talks about in what sequence one can patch Always On Availability Group.
