Recently, I was working on the AlwaysOn Availability group issue where the log records were not moving from primary to secondary replica because of the wait type “PARALLEL_REDO_TRAN_TURN”.
During the troubleshooting, when I opened the AlwaysOn Dashboard to see the Log Send Rate, I found that the Log Send Rate was coming blank against the primary replica but the secondary replica was showing a vast number of the Log Send Rate. At the time, I wondered why Log Send Rate was not showing against the primary replica on the AlwaysOn Dashboard. Ideally, it should show because the primary replica is the one which is sending log records to secondary replicas.
AlwaysOn Dashboard View
For example, if we look at the below snapshot, the Log Send Rate is only showing against the secondary replicas instead of the primary replica.
Later on, I was happened to had a discuss with SQL Guru Paul Ou Yang on this who gave a great insight – “Suppose, if you got more than one secondary replicas and wanted to know the Log Send Rate for each secondary replica, it wouldn’t be possible to get that information from the primary replica. Therefore, seeing the Log Send Rate on the secondary replica make more sense compare to seeing it from the primary replica.”
I hope you find it useful information!
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