In 5.5, a crashing, regression bug exists if you use SELECT COUNT(DISTINCT) *and* one of the WHERE operands is in the Primary Key (or just a unique index).

This simple crash (if only one row is in the table) will crash mysqld.

Of course I’ve filed a bug report, but that has been nearly 3 months and no updates yet.

Here is the bug I filed (which you won’t be able to view):

http://bugs.mysql.com/bug.php?id=61842

Really, the only thing that happened to my bug report was that it was designated a duplicate of another bug (which we also cannot view):

http://bugs.mysql.com/bug.php?id=61101

Based on the id, and the submitted dates of bugs 61100 and 61102, this initial bug (61101) was filed on May 9, 2011. So, in fact, this bug has been present for over …

I recently gave a presentation at the New York Effective MySQL Meetup on the new features of, and some of the compelling reasons to upgrade to MySQL 5.5. There are also a number of new MySQL variables that can have a dramatic effect on performance in a highly transactional environment, innodb_buffer_pool_instances and innodb_purge_threads are just two to consider.

For more information on all the new variables, status, reserved words and benchmarks of new features you can Download Presentation Slides.

Download PDF Presentation
Download Audio

There are a number of significant new features in MySQL 5.5 including semi-synchronous replication, SIGNAL and RESIGNAL, the PERFORMANCE_SCHEMA, additional STATUS variables, new partitioning options, different default storage engine, better UTF8 support and removal of deprecated functions just to list key considerations.

However some of the performance improvements are worth the investment of time. For a high concurrency InnoDB environment one new configuration alone can provide a …

Reading MySQL security: inconsistencies I remembered a few related experiments that I did several years ago when I was studying for the MySQL certification. The first fact that came to mind is about the clause "WITH GRANT OPTION", which can only be given on the full set of options, not on a single grant. For example

GRANT INSERT,DELETE,UPDATE on world.* to myuser identified by 'mypass';
GRANT SELECT on world.* to myuser identified by 'mypass' WITH GRANT OPTION;
show grants for myuser\G
*************************** 1. row ***************************
Grants for myuser@%: GRANT USAGE ON *.* TO 'myuser'@'%' IDENTIFIED BY PASSWORD '*6C8989366EAF75BB670AD8EA7A7FC1176A95CEF4'
*************************** 2. row ***************************
Grants for myuser@%: GRANT SELECT, INSERT, UPDATE, DELETE ON `world`.* TO 'myuser'@'%' WITH GRANT …

Some time ago I wrote about MySQL 5.5 semi-synchronous replication. Since then, I have wanted to benchmark the overhead of semi-synchronous replication with a decent server. Now the occasion presented itself, thanks to some related business that I had to benchmark, and thus I did a few simple runs with and without semi-synchronous replication enabled, to see the impact of this feature on performance. If you haven't read the article on semi-synchronous replication, the bottom line is that, with this feature enabled, the master waits until at least one slave has acknowledged receipt for the data before returning a positive result to the client. This means that for each commit there are two network calls between master and slave. My gut feeling was that this feature would be costly in terms of query response time, although I was not prepared to …

  I am excited to see that MySQL 5.5 GA (5.5.8) has been finally released . All of my ex-colleagues at MySQL/Oracle have done amazing jobs. I was also positively surprised that 5.5 was released on schedule:). So far I have felt that Oracle is leading MySQL development and product management very well.
  5.5 has lots of practical features not only for web services providers, but also for enterprise users. Especially I like the following features.
Improved concurrency  Very often lots of concurrent sessions access to the same table. In such cases, one of MySQL internal global mutexes (LOCK_open) becomes very hot and serious concurrency problems have happened. Increasing table_cache have caused even negative impacts (because MySQL has to do linear search here. See bug#33948 for details). In 5.5, the problem has been fixed. Here is a very simple concurrent PK …

The first addition is something that users of stored routines have been waiting for since MySQL 5.0. No, it is not SIGNAL and its close associate RESIGNAL, which have been publicized enough. I am talking about the stored routine parameters, for which now there is a dedicated table in the information_schema.
Let's see an example, with a simple …

I have been looking forward to the general availability (GA) release of MySQL 5.5 since is was publically announced in September that we would see this in 2010. While I already have a production client with 5.5.7rc, the badge of general availability is a great way to promote why environments should consider moving to using MySQL 5.5. Here is my quick short list of why I’d promote moving to MySQL 5.5.

1. Improved integration

The first significant improvement is that InnoDB is now again firmly a default included storage engine. The InnoDB plugin 1.1.x is now the builtin version of the engine, not a plugin version. Also the 1.1.x version has continued improvements over the 1.0.x version available as an included but not enabled plugin in current MySQL 5.1.x versions. Removing the complexity for end users over the choice of InnoDB and the necessary configuration changes is a great simplification. The introduction in the InnoDB plugin …

An update of MySQL from 5.0 to 5.5 on CentOS 5.5 64bit has not resulted in a good experience. The mysqld process would then crash every few minutes with the following message.

101120 8:29:27 InnoDB: Operating system error number 22 in a file operation.
InnoDB: Error number 22 means ‘Invalid argument’.
InnoDB: Some operating system error numbers are described at
InnoDB: http://dev.mysql.com/doc/refman/5.1/en/operating-system-error-codes.html
InnoDB: File name /tmpfs/#sql6cf3_5c_0.ibd
InnoDB: File operation call: ‘aio write’.
InnoDB: Cannot continue operation.

The work around was to change the tmpdir=/tmpfs (which was a 16G tmpfs filesystem) to a physical disk.

The referenced URL didn’t provide any more information of help. Unlike Bug #26662 O_DIRECT is not specified as the flush method.

In my continuing MySQL 5.5 blog series, today I am covering what's new on the replication front.  MySQL replication is my favorite server feature and what drew me to MySQL during my tenure with Embarcadero Technologies.  Others seem to agree as based on community and customer surveys, MySQL replication is the most popular and widely used database feature.  Mostly because it is easy to set up and ease, it enables scalability and provides a pretty robust solution for data redundancy, backup and overall availability.  In MySQL 5.5 replication has been enhanced in response to user requests that MySQL replication:

• Ensure data consistency between master and slave servers
• Immediately detect if replication is not working
• Allow a crashed slave to automatically recover from the master relay log
• Allow users to filter …