Within MySQL, there’s a piece called a storage engine that reads and writes to disk on your behalf when you execute a query. It controls the way that your data is stored on disk. With MySQL, you can change what storage engine you use, which is helpful since every engine has different advantages and downsides, and you can select which engine to use based on your workload. There are two main engines: MyISAM and InnoDB. MyISAM was the default engine before MySQL 5.5 and it’s been there since the beginning. It’s also not crash-proof, it doesn’t have foreign keys, and it’s not transactional. InnoDB, on the other hand, has all these features.

What happens if you use MyISAM

No Safety Belt

Grooveshark (a popular music site) in …

I recently came across an issue trying to connect to a MySQL server using the mysql client. It appeared as through the connection was hanging.

A subsequent connection using the -A option highlighted the problem with the previous connection stuck in the state “Waiting for table metadata lock”.

mysql> SHOW PROCESSLISTG
*************************** 1. row ***************************
     Id: 37
   User: root
   Host: localhost
     db: tmp
Command: Query
   Time: 90
  State: preparing
   Info: create table missing as select id from AK where id not in (select id ..
*************************** 2. row ***************************
     Id: 38
   User: root
   Host: localhost
     db: tmp
Command: Field List
   Time: 50
  State: Waiting for table metadata lock
   Info:
*************************** 3. row ***************************
     Id: 39
   User: root
   Host: localhost
     db: tmp
Command: Query
   Time: 0
  State: init
   Info: show processlist …

Yesterday we had our third Madrid MySQL users group meeting. That was quite interesting.  Thanks go to Juan for his presentation.

We plan the next meeting on January 16th after the New Year is out of the way. If you are interested in MySQL and happen to be in Madrid please consider coming to see us.

More information about the next meeting can be found on the group’s web page. Note: The meeting will be in Spanish. I look forward to seeing you.

Next week the US celebrates Thanksgiving Day. For those that are American or live here, this is a significant event. Three different experiences recently have lead me to write this request for ALL MySQL community members to give thanks to those that have contributed to the MySQL ecosystem. I have made a commitment to myself, and I would like to challenge others to write one book review per week in December, that’s 4 book reviews to the MySQL books that I have on my bookshelf that have made an impact in some way. I ask others to give it a go too.

It only takes a few minutes to pen a comment on Amazon, or a publishers site, but to authors it means so much more. I can only speak for myself, but any comment; good, bad or ugly; helps to know you are out there and you took the time to acknowledge somebody’s work of art (in this case a publication).

I only have to look at my bookshelf and I find the following MySQL books (in …

Translating theory to practice is never easy. Morgan gives us the right steps in a play environment to move from dev.mysql.com native MySQL rpm’s to the new MySQL yum repository. I thought I would try it out.

1. Confirming existing packages

A necessary step, however immediately I have more dependencies including Perl DBD (used in several utilities) including MHA.

$ sudo su -
$ rpm -qa | grep -i mysql
MySQL-devel-5.6.13-1.el6.x86_64
MySQL-test-5.6.13-1.el6.x86_64
MySQL-shared-compat-5.6.13-1.el6.x86_64
MySQL-server-5.6.13-1.el6.x86_64
perl-DBD-MySQL-4.013-3.el6.x86_64
MySQL-client-5.6.13-1.el6.x86_64
MySQL-embedded-5.6.13-1.el6.x86_64
MySQL-shared-5.6.13-1.el6.x86_64
mha4mysql-node-0.54-1.el5.noarch

A further trap in the more complex real-world environments, in my case the installation of Percona …

Using the MySQL 5.6 Performance Schema it is very easy to see what is actually running on your MySQL instance. No more sampling or installing software or worrying about disk I/O performance with techniques like SHOW PROCESSLIST, enabling the general query log or sniffing the TCP/IP stack.

The following SQL is used to give me a quick 60 second view on a running MySQL system of ALL statements executed.

use performance_schema;
update setup_consumers set enabled='YES' where name IN ('events_statements_history','events_statements_current','statements_digest');
truncate table events_statements_current; truncate table events_statements_history; truncate table events_statements_summary_by_digest;
do sleep(60);
select now(),(count_star/(select sum(count_star) FROM events_statements_summary_by_digest) * 100) as pct, count_star, left(digest_text,150) as stmt, digest from events_statements_summary_by_digest order by 2 desc;
update setup_consumers set …

Recently a client asked me how long it would take for an ALTER TABLE to complete. Generally the answer is “it depends”. While this was running on a production system I tried with the Performance Schema in MySQL 5.6 to work out some answer to this question. While I never got to investigate various tests using INPLACE and COPY for comparison, Morgan Tocker made the request for experiences with online ALTER in A closer look at Online DDL in MySQL 5.6. Hopefully somebody with more time can expand on my preliminary observations.

Using Mark Leith’s ps_helper (older version) I monitored the File I/O to see if I could determine when using innodb_file_per_table the percentage of table writing to be completed.

Other data access on this slave server was disabled, …

I was really pleased to see the announcement by Oracle MySQL yum repositories that they have now produced a yum repository from where the MySQL RPMs they provide can be downloaded. This makes keeping up to date much easier. Many companies setup internal yum repositories with the software they need as then updating servers is much easier and can be done with a simple command. For many people at home that means you set this up once and don’t need to check for updates and do manual downloads, but can do a quick yum update xxxx and you get the latest version. Great!  This new yum repository only covers RHEL6 did not include RHEL5 which is not yet end of life and still used by me and probably quite a lot of other people. I filed bug#70773 to ask for RHEL5 support to be …

Working with MySQL 5.6 under CentOS 6.4 I came across the following problem with MySQL reporting it did not shutdown successfully.

$ sudo su -
$ service mysql stop
Shutting down MySQL................................................................................................................................................................................................................................................................................................
......................................................................................................................................................................................................................................................................................................... …

The announcement of the MySQL Yum repositories was a long overdue request on my wish list. While it was possible to find MySQL at http://public-yum.oracle.com/ it was not the GA version MySQL 5.6. (As I write this post, I check and find that indeed it now appears this may be possible http://public-yum.oracle.com/repo/OracleLinux/OL6/MySQL56/).

I have previously installed MySQL 5.6.13 via rpms downloaded from MySQL Downloads, so I expected the upgrade to be straightforward. Following Chapter 3. Upgrading MySQL with the MySQL Yum Repository I …