On Mon, Mar 22, 2010 at 1:05 PM, Toru Maesaka <[email protected]> wrote: > Hi! > > Would it make sense to have an engine-level option to tell the > optimizer to prioritize index use at all times? Something along the > line of HA_PRIORITIZE_INDEX.
Hi Toru! By "prioritize" I'm assuming you mean "always prefer an index scan over a table scan"? Or do you mean something else? > I'm saying this because the relationship between > Cursor::records_in_range() and HA_READ_RANGE seems important to > effectively perform range scans at the moment. I tried purposely > returning a constant small cost factor in records_in_range() but it > seems that the range search will fail if the number of estimated rows > (in my case a total lie) is significantly smaller than the number of > actual rows in the table. If I don't set, HA_READ_RANGE then it seems > Drizzle will resort to a table scan (despite knowing that > 'possible_keys' exist in EXPLAIN). > > Preferably, I don't want to count through the number of rows in a > range for the optimizer on every simple query. Although... a > completely dishonest implementation of records_in_range() would dirty > the EXPLAIN statement result. So there is definitely a downside to > what I was experimenting with. Actually, this is precisely what InnoDB does. :( Not only does this result in a call to malloc() for a copy of the MySQL key value coverted into InnoDB's internal format, but it also results in a new InnoDB mem_heap allocation and a call to btr_estimate_n_rows_in_range(). For *every* call to Cursor::records_in_range(). Not exactly efficient...I agree that the interface and implementation could be much simpler and cleaner. -jay > It would be great to hear what you all think :) > > - Toru > > _______________________________________________ > Mailing list: https://launchpad.net/~drizzle-discuss > Post to : [email protected] > Unsubscribe : https://launchpad.net/~drizzle-discuss > More help : https://help.launchpad.net/ListHelp > _______________________________________________ Mailing list: https://launchpad.net/~drizzle-discuss Post to : [email protected] Unsubscribe : https://launchpad.net/~drizzle-discuss More help : https://help.launchpad.net/ListHelp
