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This wait type is when a thread is waiting while helping a background lazy writer thread and the system is under memory pressure with a heavy read and write workload. When a thread uses a free buffer in the buffer pool, and the free list looks low, the thread will call a routine to help replenish the free list by writing dirty pages to disk. If there are already a lot of outstanding writes, instead of issuing more writes, the thread instead waits and then loops.

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Added in SQL Server version:


Removed in SQL Server version:


Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 1099 in 2016 RTM. After 2016 RTM, you must check the DMV to get the latest value as some map_key values have changed in later builds.

Other information:

This is a normal wait type to see for threads in a system with memory pressure and heavy read and write workload. If this is a normal workload for your server, and it is already tuned for the best performance, I would filter this wait type out.

Known occurrences in SQL Server (list number matches call stack list):

  1. TBD

Abbreviated call stacks (list number matches known occurrences list):

  1. TBD