Xaprb

It seems that a lot of people equate non-SQL databases with non-relational-ness, or malign the word relational. This is pretty much pure ignorance. If you’ve ever uttered a sentence that includes the phrase “…non-relational database…” then I have two suggestions for you.

1. Study relational algebra. At a bare minimum, read the Wikipedia article on relational algebra. There is much more you could do — take a class on the topic, or read C.J. Date’s SQL and Relational Theory (my review). Ask yourself how similar SQL is to the relational algebra. How is relational algebra different from SELECT and GROUP BY? Is relational theory about relationships between data? What part do transactions play in relational algebra? Is MySQL a relational database? What about PostgreSQL, Oracle, or DB2?
2. Now that you understand relational theory more, choose a database that you think is non-relational and write a formal proof that it is not relationally complete. Please do post a link to the proof in the comments.

The truth is, a non-relational database would be of very little use. In layman’s terms, it would mean you have some data that represents true statements, and a piece of software designed to answer questions using those facts, and you can’t answer simple first-order logic questions with the software. How is this an improvement? How is this useful?

I’ve been noticing an undeniable trend in my consulting engagements in the last year or so, and when I vocalized this today, heads nodded all around me. Everyone sees a growth in the number of cases where otherwise well-optimized systems are artificially limited by InnoDB contention problems.

A year ago, I simply wasn’t seeing the need for analysis of GDB backtraces en masse. These days, I’m writing custom tools to gather and analyze backtraces. A year ago, I simply looked at the SEMAPHORE section of SHOW INNODB STATUS. These days I’m writing custom tools to aggregate and reformat that data so I can interpret it more easily. And I’m actually seeing cases of this type of problem multiple times every week. I remember the first time I ran into a server that was literally optimized to the limit, but struggling under the load. It was something new for me, not that long ago. Oh, I’d seen it before, plenty, but was always able to point out where something could be improved without changing InnoDB itself. Now it’s commonplace: schemas are fine — check. Queries are all well-indexed — check. Everything else — check. InnoDB is bottlenecked and absolutely nothing can be improved — check.

Part of the difference is the rapidly improving hardware. It’s getting hard to buy a server with fewer than 8 or even 16 cores, and 16GB of RAM feels like something I’d install in a wristwatch. But I also suspect that if I’d been characterizing the workload of servers over time in a way that was easy to compare, I’d see a clear trend towards bigger data and more queries per second. We’re just pushing MySQL + InnoDB harder today than we ever have before.

What can be done? Well, InnoDB needs to be improved, that’s all. Oracle, Percona, Google, Facebook and others are working on it, and in many cases these efforts have yielded dramatic results. But there is still much room for improvement.

One of my colleagues, Ryan Lowe, has just heard that his session on PCI compliance with MySQL has been accepted at the upcoming MySQL conference. Ryan is highly qualified to present this topic, and not many people can say that; I certainly can’t claim that title myself. If you’re looking to learn how to make your MySQL installation PCI-compliant, there’s also not a lot of trustworthy information online. Personally — and really, no bias just because he’s my colleague — I think this is a great session for the MySQL conference, which I sometimes thought didn’t have enough diversity of topics in past years. We need more stuff like this to give people a reason to return after they’ve gone for 2 or 3 years in a row.