I have an AlwaysON AG with one primary and one secondary replica in synchronous commit mode. The databases in the AG all have autogrowth disabled (standard policy within organisation). There is planned hardware maintenance on the server that hosts the secondary replica that will result in the server being offline for 4-8 hours. My undestanding is that when this happens, the connected state of the secondary replica will change to DISCONNECTED, the send queue of the databases in the primary replica will accumulate unsent transaction log records. For as long as the secondary replica remains offline, all of the current log records remain active (autogrowth is disabled), transaction log backups will not truncate the log with the potential of the log filling. Can someone please confirm if this is correct? Is there any way we can mitigate this, ie. ensuring there's no index maintenance during this window or switching to aynschronous commit mode?
That was my understanding, but after reading this msdn article https://msdn.microsoft.com/en-us/library/ff877931%28v=sql.110%29.aspx?f=255&MSPPError=-2147217396 I am confused. There is a note that states: "If primary's session-timeout period is exceeded by a secondary replica, the primary replica temporarily shifts into asynchronous-commit mode for that secondary replica. When the secondary replica reconnects with the primary replica, they resume synchronous-commit mode."
Does this pertain to my situation as described above and if so does this mean that the potential for the transaction to fill is mitigated by design? Can this temporary shift in commit mode be seen when querying sys.availabilty_replicas or via any extended event or is it a purely a under the covers change?