Queue waits may also periodically become active even if no new packets have been put on the queue.External waits External waits occur when a SQL Server worker is waiting for an external event, such as an extended stored procedure call or a linked server query, to finish.Examples of such areas are bitmaps, large binary objects (LOBs), and the spool iterator. Occurs when a full-text crawl needs to restart from a last known good point to recover from a transient failure.The wait lets the worker tasks currently working on that population to complete or exit the current step.If waiting is excessive and cannot be reduced by tuning the query (such as adding indexes), consider adjusting the cost threshold for parallelism or lowering the degree of parallelism.Occurs when a task is waiting for a communications backlog at the network layer to clear to be able to send messages.sys.dm_exec_session_wait_stats (Transact-SQL) provides similar information by session. On SQL Database Standard and Basic Tiers, requires the Server admin or an Azure Active Directory admin account.
Occurs in a MS DTC worker session when SQL Server receives notification that the MS DTC service is not available.Returns information about all the waits encountered by threads that executed.You can use this aggregated view to diagnose performance issues with SQL Server and also with specific queries and batches.When you diagnose blocking issues, remember that external waits do not always imply that the worker is idle, because the worker may actively be running some external code. To view the tape status, query sys.dm_io_backup_tapes.If a mount operation is not pending, this wait type may indicate a hardware problem with the tape drive.