… lineitem in PK order. Hence, these benefits mean MySQL 5.5 wins. But why does Hash Join take so much more time. The… match approximately 600 rows from the table lineitem for each distinct key value, in this test case D, the joining key… possibility of existence of different join algorithms. So what does that mean to MariaDB/MySQL users right now with the state of the current…
Post: How Percona strives to remain neutral and independent
March 21, 2011 By Leave a Comment
…in the MySQL ecosystem are Percona customers, including hardware … results of product research. The distinction is subtle, but important to …insist on editorial freedom, that does not mean that we operate with blinders … other relationship, but we have what you could call an “informational” partnership…
Post: How to find MySQL queries worth optimizing ?
September 11, 2012 By 6 Comments
…=’abc’; Rows_examined=0 same as Rows_sent meaning this query is optimized quite well. Note you… the access type to the tables is “const” MySQL does not count it as access to two tables. …what is the easy way to see if query is worth optimizing ? – see how many rows query sends after group by, distinct…
Post: Two Types of MySQL Users
May 10, 2010 By 5 Comments
…Visiting customers I see 2 very distinct groups of MySQL Users Users what want cool database This is…what they are looking for. Furthermore they want solid built boring database which is easy to operate and which does…in this group. It means dangerous and unproven and this is not what they are looking…
Post: ANALYZE: MyISAM vs Innodb
September 3, 2008 By 9 Comments
… This basic information means it does not change whole that… a bit off, so what ? What really matters is not…mysql> select count(distinct c) from antest; +——————-+ | count(distinct c) | +——————-+ | 101 | +——————-+ 1 row in set (0.36 sec) mysql> select count(distinct…
Post: A common problem when optimizing COUNT()
September 20, 2008 By 19 Comments
… developers what they were trying to do with COUNT(). This is database-agnostic, not related to MySQL. The … what you think it does. You meant to count the number of distinct values, but you left out the DISTINCT keyword… for them to reply and tell me what the query means so I can optimize it. A good …
Post: Flexviews - part 3 - improving query performance using materialized views
April 4, 2011 By 20 Comments
…actually part of what the COMPLETE refresh method does during its …(using RENAME TABLE) which means that the view remains …DISTINCT, a secondary view will be built in the flexviews schema, transparently, to manage the distinct… refreshable version does not take long to refresh: mysql> call flexviews….
Post: Identifying the load with the help of pt-query-digest and Percona Server
December 29, 2011 By 3 Comments
… query in the right way. But vanilla MySQL does have its limitations, it reports only a …means it accesses these pages in memory. What it says though is that, if this query would run on a cold MySQL…every query is reading approximately 38.53 distinct InnoDB pages (meaning 616.48k of data). While you …
Post: Why MySQL could be slow with large tables ?
June 9, 2006 By 141 Comments
… MySQL. If you design your data wisely considering what MySQL can do and what… indexes. In fact even MySQL optimizer currently does not take it into …” column in this table has 10000 distinct value, so range 1..100 …MySQL Cluster) and MySQL issues IO requests one by one for query execution, which means…
Comment: A common problem when optimizing COUNT()
September 22, 2008 By 19 Comments
…(pk), key(col1) ) engine = innodb; Now what do you think MySQL will do with various types of COUNT()…(col1) a good idea? Did the user mean COUNT(DISTINCT col1) or was it someone trying to … what does the SQL mean? To return to your statement “just as good as COUNT(*), if not better,” what metric…
