OK, will have feedback in a few days. On Fri, Jan 20, 2012 at 6:45 AM, Timour Katchaounov <tim...@montyprogram.com> wrote: > Hello Mark, > > >> I want a variant of the LIMIT clause that limits the number of rows >> examined during SELECT processing. This should return OK when the >> limit is reached -- something like NESTED_LOOP_QUERY_LIMIT. While >> LIMIT can be LIMIT x and LIMIT x,y. This only supports one argument -- >> LIMIT_ROWS_EXAMINED x. Are you interested in implementing this feature >> for me? We will sponsor the work. The purpose of the feature is to >> prevent queries from taking too long when there isn't a great index >> and many rows might be filtered. >> > > After examining few alternatives, I implemented a pretty complete > prototype of LIMIT_ROWS_EXAMINED. Please have a look at the description > of the task here: > https://mariadb.atlassian.net/browse/MDEV-28 > > It is important to notice that the current implementation will stop > execution when LIMIT_ROWS_EXAMINED is reached irrespective of the > query execution strategies used (thus not only for JOINs, but also > writing/reading to temp tables, sorting, and single-table access methods > that scan too many rows). This approach also is future-proof with > respect to adding new query processing algorithms because the counting > is done at the handler level. > > The current approach is such, that it should be fairly easy to backport > the feature to almost any MariaDB/MySQL. > > Please let me know if this is what you want. If so, then I will proceed > with the remaining polishing that is in the TODO list and will get an > internal review. > > You can also have a look at the small example in the comments below the > description to get a feeling what is the behavior. > > I can also send you a patch of the current version in case you want to > play with the feature before it is pushed. > > Timour
-- Mark Callaghan mdcal...@gmail.com _______________________________________________ Mailing list: https://launchpad.net/~maria-developers Post to : maria-developers@lists.launchpad.net Unsubscribe : https://launchpad.net/~maria-developers More help : https://help.launchpad.net/ListHelp
