June 19, 2013

Post: The MySQL optimizer, the OS cache, and sequential versus random I/O

April 28, 2008 By 17 Comments

…group by fact.col1 There are indexes on all the columns in all the ways you’d expect: all the dimension columns…I/O. So now you know why one join order is faster than the other. But why didn’t …MySQL optimizer were right and each of these had to go to disk, our STRAIGHT_JOIN plan would take more than…

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Post: 3 ways MySQL uses indexes

September 12, 2009 By 28 Comments

…BY B – in these cases getting data in sorting form would require a bit more than simple range scan in the BTREE and MySQL…to couple of columns index can be simply much smaller than the data which is one of the reason…using index for group by but I think they can be pretty much looked as one of these 3…

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Post: Realtime stats to pay attention to in Percona XtraDB Cluster and Galera

November 26, 2012 By 4 Comments

…run, but this one is focused on ‘…columns in the cluster section, and it’s important to understand that this tool only currently connections to a single node (by… under the Flow group.  This is wsrep_cert…more than that coming in. Our replication is performing well, because the Flow control columns…

Filed Under: MySQL, XtraDB Cluster

Post: Implementing efficient counters with MySQL

July 1, 2007 By 16 Comments

… you choose replication (rather than partitioning) as your scaling … some cases there are more counters then there really… say “id” and “counter” columns. Using separate table …to run rather complicated group by query ? Sure it does… insert into one and process and truncate another. MySQL offers atomic…

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Post: Heikki Tuuri Innodb answers - Part I

October 26, 2007 By 19 Comments

… potentially compresses the database more than just prefix compression….table scan is only one of replacement policy optimizations… was some work done by DIKU students improving…group commit again. HT: I do not think so. Sergei Golubchik serialized the MySQL…used if the columns are the first columns in …

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Post: A case for MariaDB's Hash Joins

May 31, 2012 By Leave a Comment

…MySQL 5.5 but takes slightly more time as compared to BKA algorithm of MySQL…> ’1996-05-01′ GROUP BY o_orderkey ORDER BY num_items DESC LIMIT 10; …than Hash Join when you are joining two tables on a PK column such that both tables are read in PK order. One…

Filed Under: Benchmarks, Insight for DBAs, MySQL Tagged With: , , , , ,

Post: Shard-Query adds parallelism to queries

November 15, 2010 By 18 Comments

… thread. MySQL never takes advantage of more than a …BY RANGE COLUMNS(FlightDate) (PARTITION p2 VALUES LESS THAN (’1988-01-01′) ENGINE = InnoDB, PARTITION p3 VALUES LESS THAN…more like OLTP. Instead of getting one big chunk of data in one… ’2007-12-31′ GROUP BY carrier ORDER BY 2 DESC; .tblGenFixed…

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Comment: Database problems in MySQL/PHP Applications

August 11, 2006 By 13 Comments

…more space than… by multiple columns …group tables by certain logic, such as > you do with directories to group files. I think this makes a lot of > sense. Sometimes grouping…MySQL you might be > better of using several queries than doing complicated ones. Of > course you would rather use IN() than…

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Post: InnoDB Full-text Search in MySQL 5.6: Part 2, The Queries!

March 4, 2013 By 7 Comments

…one of these stopword tables, it simply mentions the table engine and the column…BY 3 DESC LIMIT 5; …MySQL” – odds are that an article which has 10 instances of “MySQL” might be more desirable to us than…group the search terms as a single phrase: With 5.5: mysql…

Filed Under: Insight for DBAs, Insight for Developers, MySQL Tagged With: , , , , ,

Post: Database access Optimization in Web Applications.

September 12, 2006 By 10 Comments

…GROUP BY Queries and Sort Queries – SELECT name,descr FROM titles ORDER BY…BY rank query is such – adding index on rank column…one query it is better than doing so by several queries, assuming this query would not need to analyze much more…

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