Today I’m proud to announce the first public release of our ActiveRecord database connection magic plugin: DbCharmer.

DB Charmer – ActiveRecord Connection Magic Plugin

DbCharmer is a simple yet powerful plugin for ActiveRecord that does a few things:

1. Allows you to easily manage AR models’ connections (switch_connection_to method)
2. Allows you to switch AR models’ default connections to a separate servers/databases
3. Allows you to easily choose where your query should go (on_* methods family)
4. Allows you to automatically send read queries to your slaves while masters would handle all the updates.
5. Adds multiple databases migrations to ActiveRecord

Installation

There are two options when …

I have for the first time seen a client implement MySQL Resource Limits. I got the following error tying to connect to the database.

$ mysql -udba -p
ERROR 1226 (42000): User 'dba' has exceeded the 'max_user_connections' resource (current value: 10)

I see from the documentation the ability to see the limits in the mysql.user table. I see this is included in the SHOW GRANTS output.

SHOW GRANTS for 'dba'@'%';
+--------------------------------------------------------------------------------------------------------------------------------------------+
| Grants for dba@%                                                                                                                         |
+--------------------------------------------------------------------------------------------------------------------------------------------+
| GRANT ALL …

Maatkit is a pretty useful set of utilities for MySQL. From their site:

You can use Maatkit to prove replication is working correctly, fix corrupted data, automate repetitive tasks, speed up your servers, and much, much more.

One of the first things you can do after installing the toolkit (which may already be installed if you are running CentOS or Debian) is to run the mk-audit utility. It will give you a nice summary of your server, as well as point out potential problems in your configuration.

Here's a list of all the utilities included in Maatkit:

• mk-archiver Archive rows from a MySQL table into another table or a file.
• mk-audit Analyze, summarize and report on MySQL config, schema and operation
• mk-checksum-filter Filter checksums from …

I’ve had plenty of comments on specific products to Monitoring MySQL Options before providing the completed list. Here are the results from my survey to give everybody a more complete list.

With IntelliJ now being available under an Open Source license, developers have another option to choose from when it comes to Java-based IDEs/Frameworks (Eclipse and NetBeans being the other two prominent ones). Choice is always good, and being an Open Source enthusiast, I of course welcome JetBrain's move!

However, as I'm not really a heavy GUI-based IDE user myself, I can't really comment on which one is the best. These kind of discussions tend to turn into a Holy War anyway... In the end it's likely that each of them gets the job done and you have to come to your own conclusions, based on your personal preference and requirements.

I personally would be interested in …

My recent poll What alert monitoring do you use? showed 25% of the 58 respondents to bravely state they had no MySQL monitoring. I see 1 in 3, ~33% in my consulting so this is consistent.

There is no excuse to not have some MySQL Monitoring on your production system. At the worse case, you should be logging important MySQL information for later analysis. I use my own Logging and Analyzing scripts on every client for an immediate assessment regardless of what’s available. I combine that with my modified statpack to give me immediate text based analysis, broken down by hour chunks for quick reference. These help me in troubleshooting, but they are …

I had trouble today on a client site using my MySQL power tools Maatkit and Statpack.

$ ~/scripts/statpack.py --files=mysql.status.091015.080001.txt,mysql.status.091015.090001.txt
Traceback (most recent call last):
  File "/home/rbradfor/scripts/statpack.py", line 563, in ?
    main()
  File "/home/rbradfor/scripts/statpack.py", line 527, in main
    locale.setlocale(locale.LC_NUMERIC, '')
  File "/usr/lib64/python2.4/locale.py", line 381, in setlocale
    return _setlocale(category, locale)
locale.Error: unsupported locale setting

$ cat /var/log/slow-query.log | ./mk-query-digest
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LANGUAGE = (unset),
        LC_ALL = (unset),
        LANG = "e_US"
    are supported and installed on your system.
perl: warning: Falling back to the standard …

Q: What SQL is running on your MySQL database server now?
A: The bane of pain for MySQL DBA’s when there is no official MySQL instrumentation that is dynamic and fine grained sufficiently to solve this problem at the SQL interface.

While hybrid solutions exist, the lack of dynamic and real-time are the issues. There is however great work being done by Baron and others on Maatkit mk-query-digest and packet sniffing the MySQL TCP packets.

$ sudo tcpdump -i eth0 port 3306 -s 65535  -x -n -q -tttt | ./mk-query-digest --type tcpdump
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
# Caught SIGINT.
5444 packets captured
8254 packets received by filter
2809 packets dropped by kernel
# 2.1s user time, 40ms system time, 22.23M rss, 57.60M vsz
# …

There are many areas you need to review when addressing MySQL performance such as current database load, executed SQL statements, connections, configuration parameters, memory usage, disk to memory ratio, hardware performance & bottlenecks just to name a few.

If you were to just look at the data that is held in the database, what would you consider?
Here are my tips, when looking just at the data.

1. What is the current database size?
2. What is the growth of data over time, say daily, weekly?
3. Which are the 2 largest tables now?
4. What 2 tables are growing the fastest?
5. What tables have greatest churn, specifically DELETE’s?
6. How often do you optimize your tables?
7. What is your archiving/purging strategy? Do you even have one?
8. Review data types? I average 25% reduction in footprints, just by choosing optimal data types, generally with zero …

More importantly, how often to you confirm access to your server and database with that alert monitoring?

With a client yesterday the primary database server while still usable and serving connections for a while, but was not accessible via SSH to investigate performance issues. It eventually became non responsive and required a physical reboot. With alert monitoring for system availability only recorded every 5 minutes this was simply too long a delay.

This lead to a discussion with more questions then answers including.

• How often should you ping your server(s), both internally and externally?
• How often do you connect physically to your server for confirmation, e.g. a ssh keyed authentication test?
• How often do you perform a physical database connection test?
• How often do you do an end to end test, including http request to database query test?

As with all of …