We suspect that our servers do too much extra disk IO in ha_innobase::records_in_range to determine selectivity for indexes that don't get used in a query. For example when there are multiple indexes that might be used, I assume that the MySQL optimizer calls records_in_range for each and I know that InnoDB does two index lookups per call to find the leaf blocks for the start and stop predicates of the index scan. For the index that is used on the query any disk IO done in records_in_range isn't wasted. We can think of it as prefetch. But for the other indexes that disk IO is likely to be wasted. I rarely touch or even read optimizer code in MySQL. How difficult would it be to have an option to either not call records_in_range when a hint is used (such as FORCE INDEX or REALLY FORCE INDEX)? The alternative is to figure out in records_in_range when the special hint has been used for an index other than the one for which records_in_range was called and return a large value without doing index lookups for all but the hinted index. -- Mark Callaghan mdcallag@gmail.com