… performance of UNION vs MySQL 5.0 index merge algorithm Sinisa pointed out I should be using UNION ALL instead of simple UNION in my… 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…
Post: Multi Column indexes vs Index Merge
September 19, 2009 By 30 Comments
… it can lookup the row pointers from all indexes, intersect them and when lookup the … i1,i2 | 4,4 | NULL | 299364 | Using sort_union(i1,i2); Using where | +—-+————-+———+————-+—————-+——-+———+——+——–+————————————–+ 1 row in …
Post: Identifying the load with the help of pt-query-digest and Percona Server
December 29, 2011 By 3 Comments
…=1325146286; select count(*) from auto_inc; Note that logging all queries in this fashion as opposed to the general…time, 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 wp…
Comment: Possible optimization for sort_merge and UNION ORDER BY LIMIT
October 5, 2007 By 10 Comments
[...] I was comparing performance of UNION vs MySQL 5.0 index merge algorithm Sinisa pointed out I should be using UNION ALL instead of simple UNION in my benchmarks, and he was [...]
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 …Also Full Table Scan is preferred for Q4 in all cases but in case of high cardinality multiple … not to do Index merge (either intersection or union) but instead do full table scan or access …
Comment: UNION vs UNION ALL Performance
December 5, 2007 By 13 Comments
[...] Warum? UNION vs UNION ALL Performance | MySQL Performance Blog __________________ Siste gradum teque aspectu ne subtrahe nostro! Quem fugis? Extremum fato, quod [...]
Comment: UNION vs UNION ALL Performance
October 12, 2007 By 13 Comments
[...] Peter Zaitsev of the MySQL Performance Blog compares the performance of UNION vs. UNION ALL. [...]
