open life blog
This post is about a fairly technical detail of how Galera works. I'm writing it down in preparation for testing this feature so that I can agree with Alex whether to file a bug or not. I'm sharing it on my blog just in case someone else might benefit from learning this.
Galera 2.0 introduces rolling schema upgrades. This is a new way to do non-blocking schema changes in MySQL.
As the name suggests, it is done as a rolling upgrade. Having seen clusters doing rolling upgrades before, I assumed this is what happens:
- Execute alter table on Node 1.
- Node 1 is removed from the cluster and stops processing transactions.
- Node 1 completes alter table.
- Node 1 re-joins cluster and catches up so that it is in sync.
This is the second and final part of my notes from the MySQL conference. In this part I'll focus on the technical substance of talks I saw, and didn't see.
More than ever before I was a contributor rather than attendee at this conference. Looking back, this resulted in seeing less talks than I would have wanted to, since I was speaking or preparing to speak myself. Sometimes it was worse than speaking, for instance I spent half a day picking up pewter goblets from an egnravings shop... (congratulations to all the winners again :-) Luckily, I can make up for some of that by going back and browse their slides. This is especially important whenever 2 good talks are scheduled in the same slot, or in the same slot when I was to speak. So I have categorized topics here along various axes, but also along the "things I did see" versus "things I missed" axis.
My own talks
I have finally recovered from my trip to Santa Clara enough that I can scribble down some notes from this year's MySQL Conference. Writing a travel report is part of the deal where my employer covers the travel expense, so even if many people have written about the conference, I need to do it too. And judging from the many posts for instance from Pythian's direction, Nokia is perhaps not the only company with such a policy?
There has usually always been something that can be called a "soft keynote". Pirate Party founder Rick Falckvinge speaking at a database conference is a memorable example (I still keep in touch with him, having met him at the Hyatt Santa Clara). This year there was one less day, and therefore less keynotes. The soft keynote was therefore taken care of by Baron using some time out of Peter's opening keynote. Baron's talk was an ode to the conference itself, underscoring the meaning of the conference beyond just learning about technology. Sharing his own journey from a numb ASP.NET coder ("a good day at the office was when I changed a table based layout to pure CSS ...but nobody else seemed to care.") to his role today, he challenged people to network, make new friends and new revolutionary ideas. To me, it was a great opening keynote (and quite obviously would have made less sense on the last day of the conference). The talk, including Peter's part, is available on Percona.TV.
Winners of the 2012 MySQL Community Awards were announced at the Percona Live MySQL Conference and Expo just a few hours ago:
In terms of continuing with MySQL traditions, it has been my privilege the past years to be the secretary of the MySQL Community Awards panel. We have so many amazing persons, products and companies in this community. One of the nicest thing we can do to each other, and what really builds and fuels a community, is to show appreciation and say thanks to people that really deserve it.
Attached are slides and a excercise spreadsheet for the How to evaluate which MySQL High Availability solution best suits you tutorial.
We will use the spreadsheet after the break, please download it now.
So yesterday I introduced the newly committed HTTP JSON key-value interface in Drizzle. The next step of course is to create some simple application that would use this to store data, this serves both as an example use case as well as for myself to get the feeling for whether this makes sense as a programming paradigm.
Personally, I have been a fan of the schemaless key-value approach ever since I graduated university and started doing projects with dozens of tables and hundreds of columns in total. Especially in small projects I always found the array structures in languages like PHP and Perl and Python to be very flexible to develop with. As I was developing and realized I need a new variable or new data field somewhere, it was straightforward to just toss a new key-value into the array and continue with writing code. No need to go back and edit some class definition. If I ever needed to find out what is available in some struct, I could always do dump_var($obj) to find out. Even large projects like Drupal get along with this model very well.
The thing I really like with open source is the feeling you get when people just show up from nowhere and do great things to some code you originally wrote. Thanks to this miracle, I can now also present to you version 0.2 of the Drizzle JSON HTTP support, featuring a "pure JSON key-value API" in addition to the original "SQL over HTTP" API in 0.1 version. Let's recap what happened:
- At Drizzle Day 2011, I proposed that Drizzle should make available a JSON NoSQL interface. Stewart took the bait and published json_server 0.1 a week later. This API still uses SQL, it's just that the client protocol is HTTP and JSON, into which the SQL is embedded. So I suppose it's not as sexy as real NoSQL, but pretty cool nevertheless.
- At the end of last Summer I had a lot of dead time so I started playing with Stewart's code to see what I could do. I added a new API in addition to Stewart's SQL-over-HTTP API that supports key-value operations in pure JSON, similar to what you see in CouchDB, MongoDB or Metabase. I got it working quite well, however, I never implemented a DELETE command, because I then drifted off to more important tasks, such as revamping the Drizzle version numbering and bringing DEB and RPM packaging up to date.
- Last week a new but very promising Drizzle hacker called Mohit came by, looking for things he could do. He had already fixed a simple low-hanging-bug and wanted something more. Since he was interested in the JSON API, I asked if he wants to finish the missing piece. With my helpful advice of "there is no documentation but if you look at the demo GUI you'll probably figure it out, then just look at the code for POST and implement DELETE instead". I was afraid that wasn't really helpful, but I was busy that day. No problem, the next day Mohit had pushed working DELETE implementation. The day after that he implemented the final missing piece, a CREATE TABLE functionality. I was both impressed and excited.
There will be a book signing opportunity at the MySQL User Conference, more precisely at the Expo Hall Community Reception on Wednesday evening. You will be able to meet and talk to authors of great MySQL related books. ...and myself.