The Asynchronous dataflows depict the rates at which page cleaners—and sometimes prefetchers—are reading data and index pages into buffer pools and writing buffer pool pages to the disk across all active databases in the DB2 instance. These reads and 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 statistics and displays them just above their respective read or write rate dataflow.
W/s (asynchronous write rate)—The total number of asynchronous writes per second for all databases and partitions in the instance
R/s (asynchronous read rate)—The total number of asynchronous reads per second for all databases and partitions in the instance
The line graph that overlays each dataflow plots the instance-wide asynchronous write or read rates captured over the series of refreshes that have occurred during the Spotlight session.
Clicking in the Global Database I/O panel opens the Database Manager Summary drilldown. This drilldown provides details about all the active databases and partitions in the DB2 instance. You can select any database or partition to view details about that database, including I/O activity details.