Prior to version 5.0, MySQL could only use one index per table in a given query without any exceptions; folks that didn’t understand this limitation would often have tables with lots of single-column indexes on columns which commonly appeared in their WHERE clauses, and they’d wonder why the EXPLAIN plan for a given SELECT would [...]
A case for MariaDB’s Hash Joins
May 31, 2012 By Leave a Comment
MariaDB 5.3/5.5 has introduced a new join type “Hash Joins” which is an implementation of a Classic Block-based Hash Join Algorithm. In this post we will see what the Hash Join is, how it works and for what types of queries would it be the right choice. I will show the results of executing benchmarks [...]
Avoiding auto-increment holes on InnoDB with INSERT IGNORE
November 29, 2011 By 8 Comments
Are you using InnoDB tables on MySQL version 5.1.22 or newer? If so, you probably have gaps in your auto-increment columns. A simple INSERT IGNORE query creates gaps for every ignored insert, but this is undocumented behaviour. This documentation bug is already submitted. Firstly, we will start with a simple question. Why do we have [...]
Using Flexviews – part one, introduction to materialized views
March 23, 2011 By 3 Comments
If you know me, then you probably have heard of Flexviews. If not, then it might not be familiar to you. I’m giving a talk on it at the MySQL 2011 CE, and I figured I should blog about it before then. For those unfamiliar, Flexviews enables you to create and maintain incrementally refreshable materialized [...]
Multi Column indexes vs Index Merge
September 19, 2009 By 31 Comments
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 [...]
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) |
Stored Function to generate Sequences
April 2, 2008 By 17 Comments
Today a customer asked me to help them to convert their sequence generation process to the stored procedure and even though I have already seen it somewhere I did not find it with two minutes of googling so I wrote a simple one myself and posting it here for public benefit or my later use
Using VIEW to reduce number of tables used
September 28, 2007 By 12 Comments
Many Open Source software solutions use database per user (or set of tables per user) which starts to cause problems if it is used on massive scale (blog hosting, forum hosting etc), resulting of hundreds of thousands if not millions of tables per server which can become really inefficient. It is especially inefficient with Innodb [...]
Falcon Storage Engine Design Review
January 12, 2007 By 19 Comments
Now as new MySQL Storage engine – Falcon is public I can write down my thought about its design, which I previously should have kept private as I partially got them while working for MySQL. These thought base on my understanding, reading docs, speaking to Jim, Monty, Arjen and other people so I might miss [...]
ORDER BY … LIMIT Performance Optimization
September 1, 2006 By 100 Comments
Suboptimal ORDER BY implementation, especially together with LIMIT is often the cause of MySQL Performance problems. Here is what you need to know about ORDER BY … LIMIT optimization to avoid these problems ORDER BY with LIMIT is most common use of ORDER BY in interactive applications with large data sets being sorted. On many [...]
