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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

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

Multi Range Read (MRR) in MySQL 5.6 and MariaDB 5.5

March 21, 2012 By Ovais Tariq 10 Comments

This is the second 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 aimed at the optimizer enhancement Multi Range Read (MRR). Its available in both MySQL 5.6 and MariaDB 5.5 Now let’s take a look at [...]

Filed Under: Benchmarks, Insight for DBAs, MySQL Tagged With: InnoDB, MariaDB, mrr_buffer, multi range read, MySQL, MySQL Index Scan, MySQL Indexes, Optimization, Optimizer, query, random read, range lookup, read_rnd_buffer, secondary key lookup, sequential read

Improved InnoDB fast index creation

November 6, 2011 By Alexey Kopytov 4 Comments

One of the serious limitations in the fast index creation feature introduced in the InnoDB plugin is that it only works when indexes are explicitly created using ALTER TABLE or CREATE INDEX. Peter has already blogged about it before, here I’ll just briefly reiterate other cases that might benefit from that feature: when ALTER TABLE [...]

Filed Under: Benchmarks, Insight for DBAs, MySQL

Quick comparison of MyISAM, Infobright, and MonetDB

September 29, 2009 By Baron Schwartz 30 Comments

Recently I was doing a little work for a client who has MyISAM tables with many columns (the same one Peter wrote about recently). The client’s performance is suffering in part because of the number of columns, which is over 200. The queries are generally pretty simple (sums of columns), but they’re ad-hoc (can access [...]

Filed Under: MySQL Tagged With: Infobright, MonetDB, MyISAM, Optimizer

High-Performance Click Analysis with MySQL

December 22, 2008 By Baron Schwartz 13 Comments

We have a lot of customers who do click analysis, site analytics, search engine marketing, online advertising, user behavior analysis, and many similar types of work.Â The first thing these have in common is that they’re generally some kind of loggable event. The next characteristic of a lot of these systems (real or planned) is [...]

Filed Under: Insight for Developers Tagged With: Ideas, Optimizer, Replication, Tips, XtraDB

Multiple column index vs multiple indexes

August 22, 2008 By Peter Zaitsev 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.

Filed Under: Benchmarks, Insight for DBAs

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

April 28, 2008 By Baron Schwartz 17 Comments

In my post on estimating query completion time, I wrote about how I measured the performance on a join between a few tables in a typical star schema data warehousing scenario. In short, a query that could take several days to run with one join order takes an hour with another, and the optimizer chose [...]

Filed Under: Insight for Developers Tagged With: Optimizer, Storage Engine

MySQL 6.0 vs 5.1 in TPC-H queries

March 25, 2008 By Vadim Tkachenko 17 Comments

Last week I played with queries from TPC-H benchmarks, particularly comparing MySQL 6.0.4-alpha with 5.1. MySQL 6.0 is interesting here, as there is a lot of new changes in optimizer, which should affect execution plan of TPC-H queries. In reality only two queries (from 22) have significantly better execution time (about them in next posts), [...]

Filed Under: Benchmarks Tagged With: Optimizer

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

A case for MariaDB’s Hash Joins

Join Optimizations in MySQL 5.6 and MariaDB 5.5

Multi Range Read (MRR) in MySQL 5.6 and MariaDB 5.5

Improved InnoDB fast index creation

Quick comparison of MyISAM, Infobright, and MonetDB

High-Performance Click Analysis with MySQL

Multiple column index vs multiple indexes

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

MySQL 6.0 vs 5.1 in TPC-H queries

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