The mistake I commonly see among MySQL users is how indexes are created. Quite commonly people just index individual columns as they are referenced in where clause thinking this is the optimal indexing strategy. For example if I would have something like AGE=18 AND STATE=’CA’ they would create 2 separate indexes on AGE and STATE [...]
Talking MySQL to Sphinx
April 19, 2009 By 4 Comments
In the recently released Sphinx version 0.9.9-rc2 there is a support for MySQL wire protocol and SphinxQL – SQL-like language to query Sphinx indexes. This support is currently in its early preview stage but it is still fun to play with. A thing to mention – unlike MySQL Storage Engines, some of which as InfoBright [...]
Converting Character Sets
March 17, 2009 By 21 Comments
The web is going the way of utf8. Drizzle has chosen it as the default character set, most back-ends to websites use it to store text data, and those who are still using latin1 have begun to migrate their databases to utf8. Googling for “mysql convert charset to utf8″ results in a plethora of sites, [...]
Multiple column index vs multiple indexes
August 22, 2008 By 13 Comments
After my previous post there were questions raised about Index Merge on Multiple Indexes vs Two Column Index efficiency. I mentioned in most cases when query can use both of the ways using multiple column index would be faster but I also went ahead to do some benchmarks today.
Beware of MyISAM Key Cache mutex contention
August 12, 2008 By 10 Comments
Today I was working with the client loading data to MyISAM tables at very high rate. Hundreds of millions rows are loaded daily into single MySQL instance with bursts up to 100K of records/sec which need to be inserted (in the table with few indexes). It was good not all records had to go to [...]
Efficient Boolean value storage for Innodb Tables
April 23, 2008 By 6 Comments
Sometimes you have the task of storing multiple of boolean values (yes/now or something similar) in the table and if you get many columns and many rows you may want to store them as efficient way as possible. For MyISAM tables you could use BIT(1) fields which get combined together for efficient storage:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | CREATE TABLE `bbool` ( `b1` bit(1) NOT NULL, `b2` bit(1) NOT NULL, `b3` bit(1) NOT NULL, `b4` bit(1) NOT NULL, `b5` bit(1) NOT NULL, `b6` bit(1) NOT NULL, `b7` bit(1) NOT NULL, `b8` bit(1) NOT NULL, `b9` bit(1) NOT NULL, `b10` bit(1) NOT NULL ) ENGINE=MyISAM mysql> show table status like 'bbool' \G *************************** 1. row *************************** Name: bbool Engine: MyISAM Version: 10 Row_format: Fixed Rows: 10 Avg_row_length: 7 Data_length: 70 Max_data_length: 1970324836974591 Index_length: 1024 Data_free: 0 Auto_increment: NULL Create_time: 2008-04-24 00:41:01 Update_time: 2008-04-24 00:45:40 Check_time: NULL Collation: latin1_swedish_ci Checksum: NULL Create_options: Comment: 1 row in set (0.00 sec) |
Using MMM to ALTER huge tables
March 27, 2008 By 11 Comments
Few months ago, I wrote about a faster way to do certain table modifications online. It works well when all you want is to remove auto_increment or change ENUM values. When it comes to changes that really require table to be rebuilt – adding/dropping columns or indexes, changing data type, converting data to different character [...]
Heikki Tuuri Innodb answers – Part I
October 26, 2007 By 19 Comments
Its almost a month since I promised Heikki Tuuri to answer Innodb Questions. Heikki is a busy man so I got answers to only some of the questions but as people still poking me about this I decided to publish the answers I have so far. Plus we may get some interesting follow up questions [...]
Long PRIMARY KEY for Innodb tables
October 3, 2006 By 8 Comments
I’ve written and spoke a lot about using short PRIMARY KEYs with Innodb tables due to the fact all other key will refer to the rows by primary key. I also recommended to use sequential primary keys so you do not end up having random primary key BTREE updates which can be very expensive. Today [...]
Why Index could refuse to work ?
September 8, 2006 By 15 Comments
Have you ever seen index which refused to be used even if there is every reason for it to work (from the glance view):
1 2 3 4 5 6 7 | mysql> explain select * from article where article_id=10; +----+-------------+---------+------+---------------+------+---------+------+-------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+---------+------+---------------+------+---------+------+-------+-------------+ | 1 | SIMPLE | article | ALL | PRIMARY | NULL | NULL | NULL | 93490 | Using where | +----+-------------+---------+------+---------------+------+---------+------+-------+-------------+ 1 row in set (0.00 sec) |
Why on the earth index would not be used you would think, even if MySQL is mentioning it in “possible keys” ? Should you try to force it ?
