WL#8737: IO aware defaults for optimizer cost constants

Affects: Server-8.0   —   Status: Complete

WL#7340 introduced separate cost constants for access to data that is in a
memory buffer and data that needs to be read from a secondary storage device. To
reduce the impact that the worklog would have on performance of queries
(performance regressions) it was decided to keep the existing default values for
cost constants in WL#7340 and move changing default values to a separate worklog.

This worklog will change the default values to use different cost constants for
the cost of accessing data that is in memory and data that needs to be read from
disk.  The changes will be based on experiments with MySQL in both disk-bound
and cpu-bound settings.  However, to reduce the risk of regressions, the changes
will be somewhat conservative.

(Initially this worklog contains text copied from WL#7340 related to adjusting
cost constants.)

User Documentation
==================

*
http://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-1.html#mysqld-8-0-1-optimizer
* http://dev.mysql.com/doc/refman/8.0/en/cost-model.html#cost-model-database
(comment at end of section)