I recently gave a webinar to the LAOUC and NZOUG user groups on MySQL Idiosyncrasies that BITE.

For the benefit of many viewers that do not use English as a first language my slides include some additional information from my ODTUG Kaleidoscope presentation in June.

Thanks to Francisco Munoz Alvarez for organizing.

MySQL Idiosyncrasies That Bite 2010.07 View more presentations from Ronald Bradford.

I have uploaded my three presentations from the 2010 MySQL Users Conference in Santa Clara, California which was my 5th consecutive year appearing as a speaker.

• IGNITION – MySQLCamp for Oracle DBA – Volume I
• LIFTOFF – MySQLCamp for Oracle DBA – Volume 2
• 10x Performance Improvements – A Case Study

A full history of my MySQL presentations can be found on the Presenting page.

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MySQL has a number of global buffers, i.e. your SGA. There are also a number of per session/thread buffers that combined with other memory usage constitutes an unbounded PGA. One of the most common errors in mis-configured MySQL environments is the setting of the 4 primary per session buffers thinking they are global buffers.

Global buffers include:

• • key_buffer_size – For MyISAM Indexes (note you can define multiple key_buffer’s The MyISAM Key Cache)
  • innodb_buffer_pool_size – For Innodb …

MySQL has the same level of data integrity for numbers and strings as Oracle; when MySQL is correctly configured. By default (a reason I wish I knew why it is still the default), MySQL performs silent conversions on boundary conditions of data that will result in your data not always being what is specified. Let’s look at the following examples to demonstrate default behavior.

For numbers

mysql> DROP TABLE IF EXISTS example;
mysql> CREATE TABLE example(i1  TINYINT, i2 TINYINT UNSIGNED, c1 VARCHAR(5));
mysql> INSERT INTO example (i1) VALUES (1), (-1), (100), (500);
Query OK, 4 rows affected, 1 warning (0.08 sec)
mysql> SELECT * FROM example;
+------+------+------+
| i1   | i2   | c1   |
+------+------+------+
|    1 | NULL | NULL |
|   -1 | NULL | NULL |
|  100 | NULL | NULL |
|  127 | NULL | NULL |
+------+------+------+
4 rows in set (0.00 sec)

As you can see for one value we inserted 500, yet the value …

MySQL by default is a NON transactional database. For the hobbyist (See The Hobbyist and the Professional), startup entrepreneur and website developer this may not appear foreign, however to the seasoned Oracle DBA who has only used Oracle the concept is very foreign.

In MySQL you have to be concerned with two situations that will catch the unprepared out. The first is the default autocommit mode. This is TRUE, i.e. all statements are automatically committed on completion.

mysql> SELECT @@autocommit,TRUE;
+--------------+------+
| @@autocommit | TRUE |
+--------------+------+
|            1 |    1 |
+--------------+------+
1 row in set (0.00 sec)

The second is the storage engine used. Again a foreign term for Oracle DBA’s, a storage engine is a technology that stores and retrieves the underlying data from the …

In Oracle the default transaction isolation is READ_COMMITTED. In MySQL the default is REPEATABLE_READ. Because MySQL also has READ_COMMITTED I have seen in more then one production MySQL environment a transaction isolation of READ_COMMITTED. The explanation and ultimately incorrect assumption is the default in Oracle is READ_COMMITTED so we made that the default in MySQL.

I’m not going to discuss the specific differences of these isolation levels (see reference lines below) except to say it that READ_COMMITTED in Oracle more closely relates to the MySQL default of REPEATABLE_READ and not READ_COMMITTED. Just because the same term for a common feature exists, don’t assume the underlying functionality is the same or that either or both actually conform to the SQL ANSI standard.

While switching your MySQL environment to READ_COMMITTED is possible, there is still conjucture if this actually provides any performance improvement. …

As part of my MySQLCamp for the Oracle DBA series of talks to help the Oracle DBA understand, use and appreciate MySQL I have also developed a series of short interesting posts I have termed “Don’t Assume”. Many of these are re-occurring points during my consulting experiences as I observe Oracle DBA’s using MySQL. I am putting the finishing touches to my MySQL for the Oracle DBA series of talks and I’m excited to highlight some of the subtle differences and unique characteristics of MySQL RDBMS in comparison to Oracle and some extent other products including SQL Server.

Stay tuned for more soon.

I will be presenting at the MySQL Users Conference 2010 in Santa Clara, April 2010 two presentations from this series, …