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When is MIN(DATE) != MIN(DATE) ?

September 4, 2012 By Ernie Souhrada 5 Comments

Inspiration for this post is courtesy of a friend and former colleague of mine, Greg Youngblood, who pinged me last week with an interesting MySQL puzzle. He was running Percona Server 5.5.21 with a table structure that looks something like this:

CREATE TABLE foo (
 id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
 uid INT UNSIGNED NOT NULL,
 update_time DATETIME NOT NULL,
 ....
 INDEX `uid` (uid, update_time),
 INDEX `bar` (some_other_columns)
 ....
) ENGINE=InnoDB;

CREATE TABLE foo (

id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,

uid INT UNSIGNED NOT NULL,

update_time DATETIME NOT NULL,

....

INDEX `uid` (uid, update_time),

INDEX `bar` (some_other_columns)

....

) ENGINE=InnoDB;

When he ran this query:

SELECT MIN(update_time) FROM foo WHERE update_time IS NOT NULL AND update_time <> '0000-00-00 00:00:00';

1	SELECT MIN(update_time) FROM foo WHERE update_time IS NOT NULL AND update_time <> '0000-00-00 00:00:00';

The result came back as 2012-06-22 10:28:16. [...]

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

DROP TABLE and stalls: Lazy Drop Table in Percona Server and the new fixes in MySQL

June 22, 2012 By Ovais Tariq 33 Comments

Suppose you have turned on innodb_file_per_table (which means that each table has its own tablespace), and you have to drop tables in a background every hour or every day. If its once every day then you can probably schedule the table dropping process to run during off-peak hours. But I have seen cases where the [...]

Filed Under: Benchmarks, Insight for DBAs, MySQL

pt-online-schema-change and default values

June 21, 2012 By Peter Zaitsev 1 Comment

When I’m doing conventional ALTER TABLE in MySQL I can ignore default value and it will be assigned based on the column type. For example this alter table sbtest add column v varchar(100) not null would work even though we do not specify default value. MySQL will assign empty string as default default value for [...]

Filed Under: Insight for DBAs, MySQL

Building Indexes by Sorting In Innodb (AKA Fast Index Creation)

June 19, 2012 By Peter Zaitsev 2 Comments

Innodb can indexes built by sort since Innodb Plugin for MySQL 5.1 which is a lot faster than building them through insertion, especially for tables much larger than memory and large uncorrelated indexes you might be looking at 10x difference or more. Yet for some reason Innodb team has chosen to use very small (just [...]

Filed Under: Benchmarks, Insight for DBAs, MySQL

Announcing Percona Server 5.5.24-26.0

June 1, 2012 By Hrvoje Matijakovic 9 Comments

Percona is glad to announce the release of Percona Server 5.5.24-26.0 on June 1st, 2012 (Downloads are available here and from the Percona Software Repositories). Based on MySQL 5.5.24, including all the bug fixes in it, Percona Server 5.5.24-26.0 is now the current stable release in the 5.5 series. All of Percona‘s software is open-source and free, all the details of the release can [...]

Filed Under: MySQL, Percona Software

A case for MariaDB’s Hash Joins

May 31, 2012 By Ovais Tariq 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 [...]

Filed Under: Benchmarks, Insight for DBAs, MySQL Tagged With: batched key access, block nested loop, hash join, JOIN Performance, MariaDB, Performance

Join Optimizations in MySQL 5.6 and MariaDB 5.5

April 4, 2012 By Ovais Tariq 4 Comments

This is the third blog post in the series of blog posts leading up to the talk comparing the optimizer enhancements in MySQL 5.6 and MariaDB 5.5. This blog post is targeted at the join related optimizations introduced in the optimizer. These optimizations are available in both MySQL 5.6 and MariaDB 5.5, and MariaDB 5.5 [...]

Filed Under: Benchmarks, Insight for DBAs, MySQL Tagged With: batched key access, BKA, hash join, io, JOIN Performance, join_buffer, MariaDB, mrr_buffer, multi range read, MySQL Performance, nested loop join, Optimizer, random read, read_rnd_buffer, sequential read

Index Condition Pushdown in MySQL 5.6 and MariaDB 5.5 and its performance impact

March 12, 2012 By Ovais Tariq 12 Comments

I have been working with Peter in preparation for the talk comparing the optimizer enhancements in MySQL 5.6 and MariaDB 5.5. We are taking a look at and benchmarking optimizer enhancements one by one. So in the same way this blog post is aimed at a new optimizer enhancement Index Condition Pushdown (ICP). Its available [...]

Filed Under: Benchmarks, Insight for DBAs, MySQL Tagged With: Benchmarks, InnoDB, IO Performance, MariaDB, MySQL, MySQL Indexes, MySQL Performance, Optimizer

Troubleshooting MySQL Upgrade Performance Regressions

February 15, 2012 By Peter Zaitsev Leave a Comment

So lets say you upgraded from MySQL 5.1 to Percona Server 5.5 and instead of expected performance improvement you see your performance being worse. What should you do ? First if you followed MySQL upgrade best practices such as testing your workload with pt-upgrade the chances of this happening are rather slim. But lets assume [...]

Filed Under: Insight for DBAs, MySQL

Hijacking Innodb Foreign Keys

January 2, 2012 By Peter Zaitsev 2 Comments

I guess I’m first to post in 2012 so Happy New Year all blog readers ! Now back to HardCore MySQL business – foreign Keys. MySQL supported Foreign Keys for Innodb for many years, yet rudimentary support initially added in MySQL 3.23.44 have not been improved in new releases as much as I’d like. We [...]

Filed Under: Insight for DBAs, MySQL

When is MIN(DATE) != MIN(DATE) ?

DROP TABLE and stalls: Lazy Drop Table in Percona Server and the new fixes in MySQL

pt-online-schema-change and default values

Building Indexes by Sorting In Innodb (AKA Fast Index Creation)

Announcing Percona Server 5.5.24-26.0

A case for MariaDB’s Hash Joins

Join Optimizations in MySQL 5.6 and MariaDB 5.5

Index Condition Pushdown in MySQL 5.6 and MariaDB 5.5 and its performance impact

Troubleshooting MySQL Upgrade Performance Regressions

Hijacking Innodb Foreign Keys

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