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Understanding the maximum number of columns in a MySQL table

April 8, 2013 By Stewart Smith 5 Comments

This post was initially going to be two sets of polls: “What is the maximum number of columns in MySQL?” and “What is the minimum maximum number of columns in MySQL?”. Before you read on, ponder those questions and come up with your own answers… and see if you’re right or can prove me wrong! [...]

Filed Under: MySQL Tagged With: columns, CREATE TABLE, ddl, FRM, limits, MySQL, MySQL table, Perl, UNIREG

MySQL 5.6 vs MySQL 5.5 and the Star Schema Benchmark

March 11, 2013 By Justin Swanhart 7 Comments

So far most of the benchmarks posted about MySQL 5.6 use the sysbench OLTP workload. I wanted to test a set of queries which, unlike sysbench, utilize joins. I also wanted an easily reproducible set of data which is more rich than the simple sysbench table. The Star Schema Benchmark (SSB) seems ideal for this. [...]

Filed Under: MySQL Tagged With: InnoDB plugin, Justin Swanhart, MySQL 5.5, MySQL 5.6, Star Schema Benchmark (SSB), sysbench

InnoDB Full-text Search in MySQL 5.6 (part 1)

February 26, 2013 By Ernie Souhrada 1 Comment

I’ve never been a very big fan of MyISAM; I would argue that in most situations, any possible advantages to using MyISAM are far outweighed by the potential disadvantages and the strengths of InnoDB. However, up until MySQL 5.6, MyISAM was the only storage engine with support for full-text search (FTS). And I’ve encountered many [...]

Filed Under: Insight for DBAs, Insight for Developers, MySQL Tagged With: Ernie Souhrada, FTS, FullText Search, InnoDB, MyISAM, MySQL 5.6

The Optimization That (Often) Isn’t: Index Merge Intersection

December 14, 2012 By Ernie Souhrada 6 Comments

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 [...]

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

How to find MySQL queries worth optimizing ?

September 11, 2012 By Peter Zaitsev 6 Comments

One question I often get is how one can find out queries which should be optimized. By looking at pt-query-digest report it is easy to find slow queries or queries which cause the large portion of the load on the system but how do we know whenever there is any possibility to make this query [...]

Filed Under: Insight for DBAs, MySQL

Differences between READ-COMMITTED and REPEATABLE-READ transaction isolation levels

August 28, 2012 By Justin Swanhart 3 Comments

As an instructor with Percona I’m sometimes asked about the differences between the READ COMMITTED and REPEATABLE READ transaction isolation levels. There are a few differences between READ-COMMITTED and REPEATABLE-READ, and they are all related to locking.

Filed Under: Insight for DBAs, MySQL Tagged With: ACID, InnoDB, Locking, Transaction isolation

Full Text Search Webinar Questions Followup

August 24, 2012 By Bill Karwin 5 Comments

I presented a webinar this week to give an overview of several Full Text Search solutions and compare their performance. Even if you missed the webinar, you can register for it, and you’ll be emailed a link to the recording. During my webinar, a number of attendees asked some good questions. Here are their questions and my [...]

Filed Under: Events and Announcements, Insight for Developers, MySQL

Recovery after DROP & CREATE

August 22, 2012 By Aleksandr Kuzminsky 1 Comment

In a very popular data loss scenario a table is dropped and empty one is created with the same name. This is because mysqldump in many cases generates the “DROP TABLE” instruction before the “CREATE TABLE”:

DROP TABLE IF EXISTS `actor`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `actor` (
  `actor_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
  `first_name` varchar(45) NOT NULL,
  `last_name` varchar(45) NOT NULL,
  `last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`actor_id`),
  KEY `idx_actor_last_name` (`last_name`)
) ENGINE=InnoDB AUTO_INCREMENT=201 DEFAULT CHARSET=utf8;
/*!40101 SET character_set_client = @saved_cs_client */;

DROP TABLE IF EXISTS `actor`;

/*!40101 SET @saved_cs_client = @@character_set_client */;

/*!40101 SET character_set_client = utf8 */;

CREATE TABLE `actor` (

`actor_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,

`first_name` varchar(45) NOT NULL,

`last_name` varchar(45) NOT NULL,

`last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,

PRIMARY KEY (`actor_id`),

KEY `idx_actor_last_name` (`last_name`)

) ENGINE=InnoDB AUTO_INCREMENT=201 DEFAULT CHARSET=utf8;

/*!40101 SET character_set_client = @saved_cs_client */;

If there were no subsequent CREATE TABLE the recovery would be trivial. Index_id of the PRIMARY index of [...]

Filed Under: MySQL Tagged With: drop table, InnoDB, Recovery

Impact of memory allocators on MySQL performance

July 5, 2012 By Alexey Stroganov 11 Comments

MySQL server intensively uses dynamic memory allocation so a good choice of memory allocator is quite important for the proper utilization of CPU/RAM resources. Efficient memory allocator should help to improve scalability, increase throughput and keep memory footprint under the control. In this post I’m going to check impact of several memory allocators on the [...]

Filed Under: Benchmarks, MySQL

Find and remove duplicate indexes

June 20, 2012 By Miguel Angel Nieto 9 Comments

Having duplicate keys in our schemas can hurt the performance of our database: They make the optimizer phase slower because MySQL needs to examine more query plans. The storage engine needs to maintain, calculate and update more index statistics DML and even read queries can be slower because MySQL needs update fetch more data to [...]

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

Understanding the maximum number of columns in a MySQL table

MySQL 5.6 vs MySQL 5.5 and the Star Schema Benchmark

InnoDB Full-text Search in MySQL 5.6 (part 1)

The Optimization That (Often) Isn’t: Index Merge Intersection

How to find MySQL queries worth optimizing ?

Differences between READ-COMMITTED and REPEATABLE-READ transaction isolation levels

Full Text Search Webinar Questions Followup

Recovery after DROP & CREATE

Impact of memory allocators on MySQL performance

Find and remove duplicate indexes

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