Merlin is MySQL’s Enterprise Monitor, a system designed to monitor a number of MySQL database servers and provide useful feedback to the DBAs as to how they are running and what things may require attention.

It provides various things:

• graphs of key database and server performance indicators: load average, cpu usage and mysql specific information such as number of database connections, replication delays, buffer usage statistics, etc…
• a set of advisors which are intended to tell you if things are not configured properly and what to do to correct the problem.
• monitoring of servers which are linked together through replication
• the latest version of merlin (v2.0, which has been available since the beginning of the year) additionally adds via mysql proxy the ability to see all the queries which are …

I’m told WordWeb, a dictionary application for Windows, allows you to find words, quite unlike the MacOSX dictionary. I’ve never even found a usable dictionary when I use Linux, that doesn’t require me to go online.

The whole idea is that if I search for the phrase cure all, I get back a thesaurus entry that suggests the word panacea. OK, that example alone wasn’t so great, because cure-all tends to be a word in these dictionaries. WordWeb Online allows me to have a “reverse dictionary” result, which I think is just fabulous (as long as I have access to an Internet connection).

Does such a Mac app exist? Seems WordWeb exists for the iPhone, but their Java app, requires an Internet connection.

What’s interesting is that they sell the dictionary data. They are powered by MySQL, and if you’re wanting to grab their …

I can’t stress enough that people look at SQL statements that are being executed against your production MySQL database, and you optimize queries when you can.

Often it’s the improvement to the large number of similar queries executed that can optimize resources. In this example, we take a very simple query, and by removing an unnecessary order by, we eliminate MySQL internally creating a temporary (in memory) table.

So what’s the big deal.

• The query is simpler to read and understand
• Memory required for the connection is not assigned
• A number of internal steps are no longer required (4 of 21 logging messages, not an ideal measurement, but an indication). In this case, it was easily a 10% performance improvement for each query.

This query is executed 10-100 times per second, so the improvement in performance is significant.

mysql> explain select max(mdate) …

Are you having problems getting up to speed on MySQL? Are you asking yourself “Is there a hands-on training course we can send a developer/system admin to learn MySQL?”. In response, at 42SQL we have put together two new training courses, MySQL Essentials and MySQL Operations.

MySQL Essentials Training Details

With MySQL Essentials we tackle the core essentials that a developer/system admin/junior DBA would require in order to support an initial development environment that uses MySQL. Essentials training teaches the following skills:

• Which version of MySQL to use (including the various different variants and patches available)
• Backup, retention, and recovery strategies
• Configuration and Monitoring of MySQL
• Optimal schema and data objects configuration management
• …

It’s a shame that MySQL does not provide better granularity when you want to look at all SQL statements being executed in a MySQL server. I canvas that you can with the general log, but the inherit starting/stopping problems in 5.0, improved in 5.1, but I would still like to see the option on a per connection basis, or even a time period. MySQL Proxy can provide a solution here but also with some caveats.

You should however in a NON production environment, take the time to enable the general log and look the SQL Statements. Prior to looking at the SQL, monitoring of the GLOBAL STATUS variables combined with Statpack revealed the following in a 1 minute interval.

====================================================================================================
                                         Statement Activity …

This neat one line command can be of interest when you are rebuilding a MySQL slave and replication is currently catching up.

$ watch --interval=1 --differences 'mysql -uuser -ppassword -e "show slave status\G"'

You will see the standard SHOW SLAVE STATUS output, but the watch command presents an updated view every second, and highlights differences. This can be useful in a background window to keep an eye on those ‘Seconds Behind Master’.

*************************** 1. row ***************************
             Slave_IO_State: Waiting for master to send event
                Master_Host: 10.10.10.10
                Master_User: slave
                Master_Port: 3306
              Connect_Retry: 60
            Master_Log_File: mysql-bin.000626
        Read_Master_Log_Pos: 88159239
             Relay_Log_File: slave-relay.000005
              Relay_Log_Pos: 426677632
      Relay_Master_Log_File: mysql-bin.000621 …

I had the opportunity to review a client’s production Drupal installation recently. This is a new site and traffic is just starting to pick up. Drupal is a popular LAMP stack open source CMS system using the MySQL Database.

Unfortunately I don’t always have the chance to focus on one product when consulting, sometimes the time can be minutes to a few hours. Some observations from looking at Drupal.

Disk footprint

Presently, volume and content is of a low volume, but expecting to ramp up. I do however find 90% of disk volume in one table called ‘watchdog’;

+--------------+--------------+--------------+-------------+--------+
| table_schema | total_mb     | data_mb      | index_mb    | tables |
+--------------+--------------+--------------+-------------+--------+
| xxxxx        | 812.95555878 | …

Save time and energy: How to:

Listening to “Highway to Hell” in an Oxford University computer lab on a sunday afternoon writing a MySQL blog can be legitimally defined by some as sick but thats what a geek calls a relaxing yet productive sunday afternoon.

For the sake of all those CLI ambassadors like myself, I wanted to share a couple of tips and tricks I use quite often when doing my mysql db administration work / scripting. I strongly suggest any mysql dba / dev use CLI simply because thats the one thing you should always have on any machine on which mysql is installed, be it Unix, Linux, Mac, Microsoft or whatever platform you are using.

Cancelling a query you are typing without exiting to the terminal:
`\c` – How many times you ended up hitting `CTRL+C` (default process kill in most OSes) in order to cancel a command, finding yourself going back to the console and having to connect again? Nuisence? Hell …

We have a MySQL University session later today, featuring me and Trond Norbye (who works on Memcached development).

Ostensibly we are talking about some of the tools and environment details of developing on Solaris and OpenSolaris, but with a MySQL focus.

I’ve just updated the Forge page with the requisite information and a copy of the slides if you need them. Here’s the abstract:

Developing MySQL on Solaris requires you to install a suitable compiler and other tools, but you may be surprised to know that most of the material is there already, or easy to install if it’s not. But even more so, there is a huge wealth of information that you can get about your application while it’s running, both with and without using more traditional debugging methods. We’ll cover setting up a suitable environment, where to find the things you …

Today I had to swap 2 columns in one of my MySQL tables. The task, which seems easily accomplishable by a temp variable, proved to be a bit harder to complete. But only just a bit.

Here are my findings:

1. The

   UPDATE swap_test SET x=y, y=x;

   approach doesn't work, as it'll just set both values to y.

   PostgreSQL seems to handle this query differently, as it apparently uses the old values throughout the whole query. [Reference]

2. Here's a method that uses a temporary variable. Thanks to Antony from the comments for the "IS NOT NULL" tweak. Without it, the query works unpredictably. See the table schema at the end of the post. This method doesn't swap the values if one of them is NULL. Use method #3 that doesn't have this limitation. …