"Approximately equal" between Sync and Async operations for PageCleaners The documentation of num_iocleaners says:


  The parameter can be reduced if both of the following conditions are true:
  
  
  pool_data_writes is approximately equal to pool_async_data_writes
  pool_index_writes is approximately equal to pool_async_index_writes.
  
  
  The parameter should be increased if either of the following conditions are true:
  
  
  pool_data_writes is much greater than pool_async_data_writes
  pool_index_writes is much greater than pool_async_index_writes.
  


What is approximately? What is "much greater"?  What ratio?  What percentage of difference?

Does anyone have an example of values that are "approximately equal" and where the Page Cleaners value should be increased? The same info for the "much geater" values would also be appreciated.

http://www-01.ibm.com/support/knowledgecenter/SSEPGG_10.5.0/com.ibm.db2.luw.admin.config.doc/doc/r0000332.html?cp=SSEPGG_10.5.0%2F2-4-4-8-108&amp;lang=en
The idea is that you want as many of your writes as possible to be asynchronous. On the other hand, pool_data_writes will always be greater than pool_async_data_writes (ditto for index writes). 

The tolerance depends entirely on your system. If each minute you have 3 pool_data_writes and only 1 pool_async_data_writes, you obviously have twice as many synchronous writes as you have asynchronous, but it's hardly a reason for concern. 

If, on the other hand, each minute you have 300K pool_data_writes and 290K pool_async_data_writes, the difference appears to be minor, but you still have 10000/60 ~ 166 waits per second, which is pretty bad.

Please keep in mind that num_iocleaners is not the only configuration parameter that affects the write efficiency: http://www-01.ibm.com/support/knowledgecenter/SSEPGG_10.5.0/com.ibm.db2.luw.admin.perf.doc/doc/c0011381.html?lang=en

PS. In your comment you compare asynchronous reads with writes, which doesn't make much sense.