This presentation was be done by Sheeri Cabral of The Pythian Group and went into how to use SHOW ENGINE INNODB STATUS to get more information about your Innodb tables, foreign keys and transactions. This is a great presentation to learn how InnoDB works.

It also went through how to use SHOW ENGINE INNODB STATUS to tune several InnoDB variables:

innodb_adaptive_hash_index
innodb_commit_concurrency
innodb_concurrency_tickets
innodb_file_io_threads
innodb_log_buffer_size
innodb_max_purge_lag
innodb_sync_spin_loops
innodb_thread_concurrency
innodb_thread_sleep_delay

The slides can be downloaded from:

http://technocation.org/files/doc/ShowEngineInnoDBStatus.pdf

(Note that the slides open up to the middle section, which …

This is a hack, but it is a good one. I was looking at some machines on a new client, and they had the general log turned on. I was surprised, because it was a fairly busy server, and they had had many problems with the server a few months ago. I thought perhaps they had turned on the general log to diagnose a problem and forgotten to turn it off, or something similar.

When I looked at the log on disk, I saw it was a symlink to /dev/null. They were running MySQL 5.0, so I immediately realized that it was a hack to have a general log they could “turn on” without having to restart mysqld.

On a different server, I saw the same link to /dev/null done with a slow query log.

The drawbacks to doing it this way is that MySQL still has the overhead of writing to the log file. The I/O overhead is greatly reduced because the writes are to /dev/null, but there’s still overhead from other resources such as RAM, CPU, etc.

…

Why a New Utility?

A couple of months back, Tim Procter, Sheeri Cabral and I were discussing about how best to diagnose a MySQL server and/or tune its performance, automating the process as much as possible. The Performance Advisors from MySQL Enterprise do this, but most of our customers don’t have a subscription and Pythian’s collective experience is not necessary reflected by its rules.

In our daily work, we have used Major Heyden’s MySQL Tuner, Mark Leith’s Statpack and our own tools to review a MySQL server configuration parameters. However, all of these tools had limitations in regards of what we wanted to achieve. Our major …

Firstly, I have to thank my co-workers Singer Wang and Gerry Narvaja for doing a lot of the work that resulted in this comparison.

After running both InnoDB Hot Backup and Xtrabackup, we have found that there is a measurable but not large difference between the resources that Xtrabackup and InnoDB Hot Backup consume.

Xtrabackup:

• Free
  
• takes 1.1% longer (2 min during a 3 hour backup)
  
• uses 1.4% more space (1G more in a 70G backup — this was for uncompressed backups)
  
• uses 1.115% more cpu overall
  
• split as 0.12% user, 0.66% nice, 0.025% system, …

On Monday, October 12, 2009* from 7-9 pm at MIT, I will be giving a presentation explaining SHOW ENGINE INNODB STATUS for the Boston MySQL User Group. There is information about foreign keys, transactions, deadlocks and mutexes just waiting to be discovered, and I will show how to decipher the information.

For all those in the Boston area, I hope to see you there! For those who cannot be there, we will video this presentation and make it available online, and post here when the video/slides are up.

*Yes, I realize that this is a bank holiday in the US.

The easiest way to see the differences between two schemas on a non-Windows machine is to run:

mysqldump -h server1 --no-data --all-databases > file1.sql
mysqldump -h server2 --no-data --all-databases > file2.sql
diff file1.sql file2.sql

However, this will show also trivial differences, such as the value of AUTO_INCREMENT. It also does not give you a way to patch one schema to be like another.

We frequently are asked to “do a schema diff and create a script that will ‘patch’ one server.” Usually this is done to take a development or test schema and move it to production for a release.

We like to use the best tool for the job, and while diff is good, I like to use MySQL workbench. The OSS (Community) edition provides all the functionality we need for creating a schema diff and …

I spent Friday examining the systems for a more traditional consulting gig (in case you did not know, Pythian has offered more traditional consulting and emergency services in addition to our remote DBA offering for our entire 12 year history). It is a familiar story to many people — the database performance was unacceptable.

The company had a few log tables that had huge amounts of inserts and foreign keys, so they used InnoDB. Unfortunately, they also used a GUID as a primary key (which is getting more and more common these days, but long primary keys with InnoDB slow down INSERT, UPDATE and DELETE commands a great deal) — varchar(32) and utf8.

That’s right — their primary key for many of these tables was 96 bytes long (32 characters * 3 bytes per character), and as an InnoDB table, the primary key is clustered with …

Mark Callaghan posted a good test of the MySQL query cache in different versions. His tests clearly show that in 5.0.44 and 5.0.84 and 5.1.38, there is more query throughput when the query cache is disabled.

However, the tests are skewed — not on purpose, I am sure, and Mark admits he has not used the query cache before — but they are skewed all the same. Mark’s error was that he assumed he could just turn on the query cache and see if it works. Most features of MySQL do not work that way — you have to understand the strengths and weaknesses of the feature in order to use it properly.

Mark’s benchmark definitely reinforces that turning on the query cache without any knowledge of your system is a bad idea, and I agree with him on that. But it does not in any way mean that the query cache is always a bad idea. In fact, …

Mike Hogan, CEO of ScaleDB spoke at the Boston MySQL User Group in September 2009:

ScaleDB is a storage engine for MySQL that delivers shared-disk clustering. It has been described as the Oracle RAC of MySQL. Using ScaleDB, you can scale your cluster by simply adding nodes, without partitioning your data. Each node has full read/write capability, eliminating the need for slaves, while delivering cluster-level load balancing. ScaleDB is looking for additional beta testers, there is a sign up at http://www.scaledb.com.

Slides are online (and downloadable) at http://www.slideshare.net/Sheeri/scale-db-preso-for-boston-my-sql-meetup-92009

Watch the video online at …

On the 23rd of June 2008, I wrote a note saying that I had just joined Pythian. Today I am posting a similar, but different, note saying that as of the last of September, I will no longer be employed by Pythian, the time has come to look for new challenges. Although I am sad to leave, I do look forward to the future and what it may hold for me.

I wanted to take this moment to thank Pythian for having me, for having such great co-workers whom I count myself lucky to have worked with. I also want to give a special thanks to Augusto for taking care of me when I first joined, and showing me around how the company works. I must thank Paul as well—he is an exceptional person to work with, and I’ve come to value his …