Thursday, July 17, 2008

This Week in Bazaar

Welcome back to the terrarium of the Bazaar distributed version control system. Written by co-authors John Arbash Meinel, one of the primary developers on Bazaar, and Paul Hummer, who works on integrating Bazaar into Launchpad as he refines his plans for world domination from his shiny new lair.

Bazaar 1.6b3 released

The next beta release of Bazaar has just been cut, and is available at your local PPA:

The Windows installers should be available later today. This release provides lots of the shiny things that we've been talking about, like Stacked Branches, Real Weave Merge, more hooks for server-side operation, and lots of bug fixes and general polishing. The full UI for using stacked branches still needs a little bit of polishing, so the feature is not enabled by default. The functionality is all there, and if you are interested, we'd love to hear from you (kudos and complaints are equally welcome).

New updates to Gnome Bazaar Playground

Coming back from a very productive trip to Guadec, Tim Penhey has been overseeing some customizations to the Bazaar Playground for Gnome. All of the branches created at the local server in Turkey for Guadec have been added to the public playground. The Loggerhead installation has received some TLC by way of customizations to the UI. Accerciser's playground page is a good demonstration af the UI changes that have been made. The playground is actively being used by applications such as Brasero, jhbuild, Metacity and more.

One of the fun results of meeting with people at Guadec, is that it showed ways to improve Loggerhead when dealing with lots of projects and lots of branches. Work is continuing to make customizing Loggerhead's look-and-feel easier, and providing better tools for creating these "Bazaar Playgrounds" to use in evaluating Bazaar. The Bazaar developers are committed with making tools easier to use, and making the process as simple and powerful as possible.

Up and Coming Repository Format Updates

Robert Collins has been hard at work to refine how Bazaar stores its history information. We all like to have deep context, but we don't like to have to pay the penalty of downloading all of that context. Because Bazaar has a flexible repository structure, Robert has been able to play with changing the on-disk structure without major surgery to the rest of the code.

First is a change to how indexes are written, switching from a bisectable list to a btree structure. This paged structure allows us to compress the indexes, making them smaller, and faster to process remotely. It also reduces the number of lookups to find a key. (On average, a bisect search is log2N, while the btree is closer to log100N.) At the moment, he is testing this with a shared repository containing all of the projects available from in the Ubuntu apt repositories. This weighs in at around 13k branches, and somewhere around 20GB of disk space used.

Second is an update to how texts are stored. At the moment we use a simple format which places fulltexts periodically, and then stores deltas against those fulltexts. It has served us rather well, but can be improved upon. With his Group compress work, we can see a savings of as much as 2x-3x. Further, the data is stored such that you can do simple linear reads to get the base fulltext and all deltas necessary to generate a given fulltext. This reduces the pressure on indices, as you don't have to search for base texts. (Instead you just store a pointer to the start, and give the total length that needs to be read.)

These are still in development phase, but a format that uses them will likely appear in the next release (bzr 1.7).

Community Agile

Ian Clatworthy has recently released a wonderful document describing the workflow we (generally) use at Canonical. It describes how basic practices are similar to, and different from, other systems like Agile. The biggest (IMO) being a recognition that the community surrounding your project is one of the strongest and most important pieces. This has always been true in software development, but it has traditionally been somewhat hidden. Open Source has exposed just how powerful the community can be. For people interested in how software can be developed, rather than just what, I certainly recommend it.

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