I spent some time last month getting up to speed on MySQL. One of the nice perks of working at Pythian is the ability to study during the workday. They could have easily said “You are an Oracle DBA, you don’t need to know MySQL. We have enough REAL MySQL experts”, but they didn’t, and I appreciate.

So how does an Oracle DBA goes about learning MySQL?
Obviously you start by reading the docs. Specifically, I looked for the MySQL equivalent of the famous Oracle “Concepts Guide”.
Unfortunately, it doesn’t exist. I couldn’t find any similar overview of the architecture and the ideas behind the database. The first chapter of “High Performance MySQL” had a high level architecture review, which was useful but being just one chapter in a book, it lacked many of the details I wanted to learn. Peter Zaitsev’s “InnoDB Architecture” presentation had the kind of information I needed – but covered just InnoDB.

Thats really too bad because I definitely feel the lack – which I can easily tell you what Oracle does when you connect to a database, run a select, an update, commit or rollback – I can’t say the same about MySQL. So far I managed without this knowledge, but I have a constant worry that this will come back and bite me later.

Lacking a concepts guide, I read the documentation I had access to: Sheeri has nice presentations available for Pythian employees (and probably customers too. I’m not sure if she ever released them to the whole world). The official documentation is not bad either – it covers syntax without obvious errors and serves as a decent “how do I do X?” guide.

But reading docs is only half the battle. The easier half too. So I installed MySQL 5.1 on my Ubuntu from ready packages. Then I installed MySQL 5.5 from the tarball – which was not nearly as much fun, but by the time this worked I know much more about where everything is located and the various ways one can mis-configure MySQL.

Once the installation was successfull, I played a bit with users, schemas and databases. MySQL is weird – Schemas are called databases, users have many-to-many relation with databases. If a user logs in from a differnet IP, it is almost like a different user. If you delete all the data files and restart MySQL – it will create new empty data files instead. You can easily start a new MySQL server on the same physical box by modifying one file and creating few directories.

MySQL docs make a very big deal about storage engines. There are only 2 things that are important to rememeber though: MyISAM is non-transactional and is used for mysql schema (the data dictionary), it doesn’t have foreign keys or row level locks. InnoDB is transactional, has row level locks and is used everywhere else.

There are a confusing bunch of tools for backing up MySQL. MySQLDump is the MySQL equivalent of Export. Except that it creates a file full of the SQL commands required to recreate the database. These files can grow huge very fast, but it is very easy to restore from them, restore any parts of the schema or even modifying the data or schema before restoring.
XTRABackup is a tool for consistent backups of InnoDB schema (remember that in MyISAM there are no transactions so consistent backups is rather meaningless). It is easy to use – one command to backup, two commands to restore. You can do PITR of sorts with it, and you can restore specific data files. It doesn’t try to manage the backup policies for you the way RMAN does – so cleaning old backups is your responsibility.

Replication is considered a basic skill, not an advanced skill like in the Oracle world. Indeed once you know how to restore from a backup, setting up replication is trivial. It took me about 2 hours to configure my first replication in MySQL. I think in Oracle Streams it took me few days, and that was on top of years of other Oracle experience.

Having access to experienced colleagues who are happy to spend time teaching a newbie is priceless. I already mentioned Sheeri’s docs. Chris Schneider volunteered around 2 hours of his time to introduce me to various important configuration parameters, innoDB secrets and replication tips and tricks. Raj Thukral helped me by providing step by step installation and replication guidance and helping debug my work. I’m so happy to work with such awesome folks.

To my shock and horror, at that point I felt like I was done. I learned almost everything important there was to know about MySQL. It took a month. As an Oracle DBA, after two years I still felt like a complete newbie, and even today there are many areas I wish I had better expertise. I’m sure it is partially because I don’t know how much I don’t know, but MySQL really is a rather simple DB – there is less to tweak, less to configure, fewer components, less tools to learn.

Jonathan Lewis once said that he was lucky to learn Oracle with version 6, because back then it was still relatively simple to learn, but the concepts didn’t change much since so what he learned back then is still relevant today. Maybe in 10 years I’ll be saying the same about MySQL.

Juan Maiz: Connecting to MongoHq with Haskell ¶

Looks like today we’ll have some geeky stuff:

This connects, logs in, inserts and then retrieves a document in a collection.

ksankar: A path through a NOSQLSummer Reading ¶

In case you have troubles picking up the first NOSQL summer paper, you mind find this classification useful. As a side note, Bucharest was the first city organizing the event and we had quite some fun discussing freely about the CAP Theorem.

vonconrad: Which of CouchDB or MongoDB suits my needs? ¶

Anyone willing to help him out? The presented scenario is quite interesting and definitely a good fit for document databases.

Salvatore Sanfilippo:

The default and usually the preferred way for a client to chat with a Redis server is using the TCP protocol described in the Protocol Specification. In some environments the trade off of switching to a less reliable and not feature complete protocol running over UDP in order to improve latency is a good idea, so starting from Redis 2.2 there is support for a binary UDP protocol.

Based on a recent ☞ tweet it looks like the new Redis UDP protocol is already delivering some good results:

There are advantages (200k req/sec) but not so big as reported

建立数据库性能模型，这是我最近一直在思考的一个问题。这个命题还是非常有意义的，因为我们在很多情况下都需要对数据库做性能评估，容量规划和风险预测。很多DBA的优化经验都局限在一个很小的数据库技术领域内，而对整个系统的性能容量并不十分了解。我希望能够给大家一些简单的模型和经验数据，帮助大家对系统的整体性能有一个更深层次的了解。

这篇PPT可能还达不到模型的理论高度，甚至很多数据还不是十分准确，只是我个人思考的一个结果，希望能抛砖引玉，大家一起思考和进步。

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6月2日数字证书全面升级：

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安装步骤

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