… (k1, k2, k3) is an index lookup. Look at the EXPLAIN output — it accesses these first, by looking up the keywords…) = (‘Karwin’, ‘Bill’); Q: On the Dynamic Pivot, the straight join, can you explain more about why you thought about doing that and why it helped? When I did not use the STRAIGHT_JOIN…
Post: How to fix your PRM cluster when upgrading to RHEL/CentOS 6.4
May 29, 2013 By 2 Comments
….4 may break your cluster. In this post I will explain you how to fix your cluster in case it breaks… kernel config… [ OK ] Starting gfs_controld… [ OK ] Unfencing self… [ OK ] Joining fence domain… [ OK ] [root@percona1 ~]# /etc/init.d/pacemaker start… kernel config… [ OK ] Starting gfs_controld… [ OK ] Unfencing self… [ OK ] Joining fence domain… [ OK ] Starting Pacemaker Cluster Manager: [ OK ] [root@percona2…
Post: Percona MySQL University @Portland next Monday!
June 12, 2013 By Leave a Comment
… in the Cloud Matt Yonkovit, our VP of Consulting, will explain how to work with BigData effectively Justin Swanhart, our Senior… can’t afford to miss… 
So register now! Please also join the Portland MySQL Meetup group for more MySQL-focused events…
Post: EXPLAIN EXTENDED can tell you all kinds of interesting things
June 15, 2010 By 7 Comments
…` join `test`.`j3` where 0 | +——-+——+——————————————————————————-+ 1 row in set (0.00 sec) You might notice a few odd things about this EXPLAIN… that I explained used the comma syntax, but when MySQL rewrote the query it switched it to use the JOIN keyword. This… any perceived performance difference between comma join and ANSI JOIN syntax. They are intrinsically the same. Last, EXPLAIN EXTENDED can show you information…
Post: A case for MariaDB's Hash Joins
May 31, 2012 By Leave a Comment
… different queries and explain the results so that you have a better understanding of when using the Hash Join will be best… its EXPLAIN output as returned by MySQL 5.5 is as follows: SELECT s_nationkey, l_shipmode, count(*) FROM supplier INNER JOIN… its EXPLAIN output as returned by MySQL 5.5 is as follows: SELECT s_nationkey, l_shipmode, count(*) FROM supplier INNER JOIN…
Post: How adding another table to JOIN can improve performance ?
August 1, 2008 By 12 Comments
…(events) | +————-+ | 3289092 | +————-+ 1 row in set (1.04 sec) mysql> explain select sum(events) from info where d between ’2007-01… loops join – exactly what we tried to avoid. It is easy to block equality propagation by using some trivial function: mysql> explain… to trick around equity propagation to make it work) mysql> explain select sum(events) from info,dl where myday between ’2007…
Post: Join Optimizations in MySQL 5.6 and MariaDB 5.5
April 4, 2012 By 4 Comments
… is one additional join optimization in MariaDB that I would like to quickly explain here, and that is Hash Joins. Hash Join As I have told before MySQL has only supported one join algorithm and… Loop Join. MariaDB has introduced a new join algorithm Hash Join. This join algorithm only works with equi-joins. Now let me briefly explain how hash join…
Post: MySQL EXPLAIN limits and errors.
July 24, 2006 By 6 Comments
…. EXPLAIN may take long time In MySQL 5.0 with addition of greedy join the problem on looking at too many table join… an error in select in from clause EXPLAIN might never complete. Solution is to run EXPLAIN for statements in FROM clause separately… view. If you want to find more information about understanding EXPLAIN output, MySQL manual EXPLAIN page is good place to start.
Post: Joining on range? Wrong!
May 17, 2010 By 10 Comments
… we have proper indexes on all necessary columns! What does EXPLAIN have to say about this? *************************** 1. row *************************** id: 1 select… affects joins only. When you use a range condition on the first (or the only) table, it works as expected: EXPLAIN SELECT… rewritten query: EXPLAIN SELECT COUNT(1) FROM tags t JOIN products p ON p.prd_id = t.tag_prd_id JOIN items_ordered…
Post: Enum Fields VS Varchar VS Int + Joined table: What is Faster?
January 24, 2008 By 30 Comments
….085637 3) Results for INT + join: select SQL_NO_CACHE c.city from cities_join c JOIN states s ON (s.id = c… the join in this case because there is really no join: mysql> EXPLAIN select SQL_NO_CACHE c.city from cities_join c JOIN states… performance, while join performance degraded dramatically. Here is why: mysql> explain select SQL_NO_CACHE c.city from cities_join c JOIN states s…
