… with the Sakila sample database to demonstrate: mysql> SET profiling=1; mysql> pager cat > /dev/null mysql> SELECT * FROM nicer_but_slower_film… query consumed 0.18 seconds. Where did the time go? mysql> SHOW PROFILE FOR QUERY 1; +———————-+———-+ | Status | Duration | +———————-+———-+ | starting | 0.000032… subtract the SUM(DURATION) from the query’s real response time. If there were, I could add in a UNION to inject…
Post: Distributed Set Processing with Shard-Query
May 14, 2011 By 27 Comments
…, subqueries in the FROM clause, and UNION operations to operate fully in … SQL, but right now only MySQL storage nodes are supported. Amdahl…SUM(`count(*)`) AS `count(*)`, SUM(`sum(AirTime)`) AS `sum(AirTime)`, SUM(`sum(DepDelay)`) AS `sum(DepDelay)`, SUM(`sum(DepDelay >= 0) flight_delayed`) AS `sum…
Post: How adding another table to JOIN can improve performance ?
August 1, 2008 By 12 Comments
… to this problem – using IN list instead of range or UNION which however require rather serious application changes and also can…,70,80,90,100); +————-+ | sum(events) | +————-+ | 3289092 | +————-+ 1 row in set (1.04 sec) mysql> explain select sum(events) from info where d…
Post: Identifying the load with the help of pt-query-digest and Percona Server
December 29, 2011 By 3 Comments
…logging atomically, not just for new connections as in MySQL. This is very helpful for measurement as otherwise we…5% 51 0.0039 1.00 0.00 SELECT UNION wp_pp_daily_summary wp_pp_hourly_summary wp…and shows the top queries with largest impact – longest sum of run time which typically (not always) shows …
Post: Multiple column index vs multiple indexes
August 22, 2008 By 13 Comments
… queries using where clause which covers multiple columns: Q1 SELECT sum(length(val)) FROM T WHERE i=2 AND j=1… of low cardinality even though MySQL can’t use index well. You’re right MySQL can’t and MySQL does not – Full table… also worth to watchout a MySQL may decide not to do Index merge (either intersection or union) but instead do full table…
