… performance of UNION vs MySQL 5.0 index merge algorithm Sinisa pointed out I should be using UNION ALL instead of simple UNION in… LIMIT inside of union clause being cool thing. But So is UNION ALL indeed faster than UNION DISTINCT (the UNION is shortcut for UNION DISTINCT) ? Indeed it…
Post: Multiple column index vs multiple indexes
August 22, 2008 By 13 Comments
… questions raised about Index Merge on Multiple Indexes vs Two Column Index efficiency. I mentioned in most … j having both of them having 1000 of distinct values, independent on each other. I also created … not to do Index merge (either intersection or union) but instead do full table scan or access …
Post: Identifying the load with the help of pt-query-digest and Percona Server
December 29, 2011 By 3 Comments
… 0.000000 InnoDB_queue_wait: 0.000000 # InnoDB_pages_distinct: 973 SET timestamp=1325146286; select count(*) from auto_inc…, the number of tmp tables created in memory vs on-disk, percentage of queries that needed full scan…5% 51 0.0039 1.00 0.00 SELECT UNION wp_pp_daily_summary wp_pp_hourly_summary …
