The W/s dataflow depicts the rate at which page cleaners—and sometime prefetchers—are writing buffer pool pages to the database or partition. These writes are asynchronous because they are not part of the processing of program instructions—and therefore can run in parallel with database agent processes.
Page cleaners write pages to disk to ensure free pages in the buffer pool for database agents and to allow faster recovery of the database should a system crash occur. Prefetchers typically read data and index pages into the buffer pool, anticipating an application’s need for these pages. However, prefetchers might need to write pages from the buffer pool to disk to make space for the pages they are prefetching .
At each refresh, Spotlight captures the following statistic and displays it just above the write rate dataflow:
W/s (asynchronous write rate)—The number of asynchronous writes per second at the database or partition level.
The line graph that overlays the dataflow plots the asynchronous write rate captured over the series of refreshes that have occurred during the Spotlight session.
Click the W/s dataflow to open the Databases drilldown. This drilldown provides details about the database or partition that you are currently monitoring. The I/O Activity tab on the drilldown is in immediate focus to help you pinpoint I/O flow problems in the database or partition.