The AlwaysOn log transport uses a SQL Broker-like based design to send and receive messages between the primary and secondary replicas. Studying the transport behavior revealed various improvement opportunities.
Many of you have read the various materials indicating that log transportation between the primary and secondary is commonly 1/3 that of file copy speed. That is no longer the case. A SQL Server 2016 AlwaysOn database can commonly maintain 90% or better transitional throughput rate directly comparing the same workload against a standalone database.
For example, SQL Server 2014 requires ~16, thread context switches to transport a log block. SQL Server 2016 can accomplish the same transport task in 8 context switches. This can lead to a 4x to 5x improvement in log block transport throughput.
'It Just Runs Faster' - SQL Server 2016 improves the log block transportation throughput scaling AlwaysOn by 4x.
Bob Dorr - Principal SQL Server Software Engineer
Nitin Verma - Senior SQL Server Software Engineer