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SQL Server 2016 introduces multiple log writer workers to the engine. For many years the log device was limited by the capabilities of spinning media and hardware caches. The advancement of hardware caches and fast storage types (SSD, flash, …) on large installations can saturate a single log write worker.
SQL Server 2016 extended the log writer by allowing up to 4 workers for the instance. You can find out the number of log writers present in your SQL Server using the following command:
select session_id, status, command, scheduler_id, task_address, wait_type
from sys.dm_exec_requests
where command =