This category reports information about the state of buffers when they reach the pool’s wash marker. When a buffer reaches the wash marker it can be in one of three states:
“Buffers Passed Clean” reports the number of buffers that were clean when they passed the wash marker. The buffer was not changed while it was in the cache, or it was changed, and has already been written to disk by the housekeeper or a checkpoint. “% of total” reports the percentage of buffers passed clean as a percentage of the total number of buffers that passed the wash marker.
“Buffers Already in I/O” reports the number of times that I/O was already active on a buffer when it entered the wash area. The page was dirtied while in the cache. The housekeeper or a checkpoint has started I/O on the page, but the I/O has not completed. “% of total” reports the percentage of buffers already in I/O as a percentage of the total number of buffers that entered the wash area.
“Buffers Washed Dirty” reports the number of times that a buffer entered the wash area dirty and not already in I/O. The buffer was changed while in the cache and has not been written to disk. An asynchronous I/O is started on the page as it passes the wash marker. “% of total” reports the percentage of buffers washed dirty as a percentage of the total number of buffers that entered the wash area.
If no buffers pass the wash marker during the sample interval, sp_sysmon prints:
Statistics Not Available - No Buffers Entered Wash Section Yet!
