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:status: Current policy, as of 2009-08.
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:blueprint: <https://blueprints.launchpad.net/bzr/+spec/6m-cycle>
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Our users want easy access to bug fixes without other changes to the
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core product. They also want a Just Works experience across the full
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Bazaar ecosystem. To deliver the first and enable the second, we're
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adopting some standard process patterns: a 6 monthly release cycle and a
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stable branch. These changes will also have other benefits, including
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better availability of bug fixes in OS distributions, more freedom to
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remove old code, and less work for in packaging.
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============================
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The Bazaar Development Cycle
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============================
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Bazaar makes a release every four weeks, with one release candidate one
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week before the final release. We may vary this schedule from time to
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time, amongst other things to respond to bugs reported in the release
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candidate or the final release. Nevertheless, we value a regular release
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and we will normally slip only for serious bugs or regressions.
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* `Bazaar Developer Document Catalog <index.html>`_
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* `Releasing Bazaar <releasing.html>`_ -- the process for actually making
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* `Releasing Bazaar <releasing.html>`_ -- the process for actually making
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a release or release candidate.
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Bazaar will make a major release every six months, which will be supported
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at least until the time of the next major release. During this support
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period, we'll make incremental releases which fix bugs, but which do not
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change network or disk formats or command syntax, and which do not require
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We will also run a development series, which will become the next major
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release. We'll make a beta release from this every four weeks. The
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beta releases will be as stable as our current monthly releases and
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completely suitable for everyday use by users who can tolerate changes
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Having the stable series isn't a reason to cut back on QA or to make the
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trunk or development releases unstable, which would only make our job
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harder. We keep our trunk in an always-releasable state, and that should
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continue: any beta release could potentially be supported in the long
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term, but we identify particular releases that actually will be supported.
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The trunk will never be frozen: changes that pass review, other quality
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checks and that are agreed amongst the developers can always be landed
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into trunk. The only restrictions will be on branches specifically
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targeted at a release.
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2.0.0 --- 2.0.1 -- 2.0.2 -- ...
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+--2.1.0beta1 -- 2.1.0beta2 -- ... -- 2.1.0rc1 -- 2.1.0 -- 2.1.1 -- ...
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Starting from the date of a major release:
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At four-week intervals we make a new beta release. There will be no
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separate release candidate, but if a serious problem is discovered we may
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do the next beta ahead of schedule or make a point release. There will be
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about five or six releases in that series.
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In parallel with this, bugs targeted to the previous major release are
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merged into its branch. We will make bugfix releases from that branch as
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appropriate to the accumulation of changes, perhaps monthly, perhaps more
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often if there are serious bugs, perhaps much less often if no new changes
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We will then make a release candidate for the next major release, and at
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this point create a release branch for it. We will iterate release
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candidates at approximately weekly intervals until there are no bugs
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blocking the final major release.
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Compared to the current process this has approximately the same amount of
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release-related work, because the extra releases from the stable branch
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are "paid for" by not doing RCs for the development series.
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We will synchronize our major releases with Ubuntu, so that they come out
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in sufficient time for some testing and margin of error before Ubuntu's
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We value regular releases. We prefer to slip a feature or fix to
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a later release rather than to make a release late. We will normally only
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slip a release to fix a critical bug.
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The number for a six-month cycle is chosen at the start, with an increment
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to either the first field (3.0.0) or second field (3.1.0) depending on
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what we expect to be the user impact of the release. We expect releases
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that culminate in a new disk format or that require changes in how people
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use the tool will get a new major number. We can change (forward only) if
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it turns out that we land larger changes than were expected.
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We will always use the 3-digit form (major.minor.micro) even when
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referring to the initial major release. This should help clarify where a
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patch is intended to land. (eg, "I propose this for 2.0.0" is clear, while
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"I propose this for 2.0" could mean you want to make the 2.0.0 release, or
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that you just want to land on the 2.0.x stable release series.)
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Major releases (2.0.0 or 2.1.0)
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The big ones, every six months, intended to ship in distributions and
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to be used by stability-oriented users.
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Release candidate (2.0.0rc1)
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A preview of a major release, made one or a few weeks beforehand at
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the time the release branch is created. There should be few if any
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changes from the rc to the stable release. We should avoid the
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confusing phrasing "release candidate 2.0.0rc1 is released"; instead
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Bugfix releases (2.0.1)
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Based on the previous major release or bugfix; contains only bugfixes
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and perhaps documentation or translation corrections.
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A major release and its descendant bugfix releases.
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Either a major release or a bugfix release.
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Beta release (3.0.0beta1)
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Made from trunk every month, except for the month there's a major
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release. Stable and suitable for users who want the latest code and
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can live with some changes from month to month.
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The development releases leading up to a stable release.
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Bug fixes should normally be done first against the stable branch,
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reviewed against that branch, and then merged forward to trunk.
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It may not always be easy to do this, if fixing the bug requires large
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changes or the affected code is different in the stable and development
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branches. If the tradeoff does not seem worthwhile the bug can be fixed
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only in the development branch, at least in the first instance. If users
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later want the fix backported we can discuss it.
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Developers can merge the release branch into trunk as often as they like,
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only asking for review if they're making nontrivial changes or feel review
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Feature and Performance Work
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----------------------------
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Features can be landed to the development branch at any time, and they'll
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be released for testing within a month.
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Performance bugs, although important, will generally not be landed in a
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stable series. Fixing performance bugs well often requires nontrivial
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code changes or new formats. These are not suitable for a stable series.
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Performance bugs that can be fixed with a small safe patch can be
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considered for the stable series.
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Plugins that want to cooperate with this should make a series and a branch
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that matches each bzr stable series, and follow similar rules in making
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releases from their stable branch. We'd expect that plugins will make a
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release between the last development release of a series and the major
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Within a stable series, anything that breaks any known plugin is
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considered an API break and will be avoided. Before
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making each bugfix release, we'll test that code against important
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Within a development series, the focus is on helping plugin authors keep
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up to date by giving clear error messages when an interface is removed.
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We will no longer focus on letting old plugin code work with new versions
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of bzrlib, which is an elusive target in Python.
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This may mean that in cases where today a plugin would keep running but
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give warnings, it will now fail altogether with an error.
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In return we expect more freedom to change and cleanup bzrlib code without
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needing to keep old code around, or write extra compatibility shims, or
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have review turnarounds related to compatibility. Some changes, such as
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removing module-global variables, that are hard to do now, will be
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possible to do safely.
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Discussion of plugins here includes programs that import and use bzrlib
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but that aren't technically plugins. The same approach, though the
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technical considerations are different, should apply to other extensions
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such as programs that use bzr through the shell interface.
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Data and Network Formats
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------------------------
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Any development release should be able to interoperate with the previous
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stable release, and any stable release should be able to interoperate with
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the previous stable release. This is a minimum and normally releases will be
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able to interoperate with all previous releases as at present.
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Each major release will have one recommended data format which will be the
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default. The name of the format will indicate which release series (not
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specific release) it comes from: '2a' is the first supported format for
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the 2.0.x series, '2b' the second, etc. We don't mention the particular
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release that introduced it so as to avoid problems predicting precisely
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During a development series we may have a series of experimental formats.
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We will not leave people stranded if they test these formats, but we also
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won't guarantee to keep supporting them in a future release. If something
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inserted in one development release turns out to be bad it can just be
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The guarantees made above about format and network interoperation
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mean that hosting services such as Launchpad, Savannah, FedoraHosted,
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and Sourceforge could choose to run either the stable or beta versions.
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They might find it useful to run the beta version on their own beta
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Simultaneous Installation
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-------------------------
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Some people may want to simultaneously install and use both a stable
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release and development release.
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This can be handled in various ways either at the OS packaging or the
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Python level. We don't propose to directly address it in the upstream
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source. (For example, we will not change the bzrlib library name from one
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release to the next.)
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The issue already exists with people who may want to use for example the
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previous bzr release and the trunk. There is a related issue that plugins
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may be compatible with only some of the Bazaar versions people want to use
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at the same time, and again that is something that can be handled
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OS distributors will be recommended to ship the bzr stable release that
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fits their schedule, the betas leading up to that release during their own
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beta period, and the bugfix releases following on from it. They might
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also choose to offer the beta releases as an alternative package.
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At present we have three upstream-maintained PPAs containing Ubuntu
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packages of Bazaar: ``~bzr-nightly-ppa``, ``~bzr-beta-ppa`` (rcs and
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releases) and ``~bzr`` (ie stable). We will keep these PPAs, and reorient
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beta to contain the monthly beta releases, and the stable PPA to contain
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stable releases, their release candidates, and bugfixes to those releases.
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Some platforms with relatively less active packagers may choose to ship
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only the stable releases. This is probably better than having them only
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intermittently or slowly ship the monthly releases.
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Binary installers should use a version number like '2.0.0-1' or
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'2.0.0beta1-1' so that the last component just reflects the packaging
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version, and can be incremented if a new installer is made with no
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upstream source changes.
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Code Freeze vs Announcement
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---------------------------
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We will separate the code freeze for a particular release from its actual
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announcement, allowing a window of approximately one week for plugins to
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be released and binary installers to be built. On the date the
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announcement is published, people will be able to easily install it.
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Work spanning multiple releases is typically tracked in the bug tracker,
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and summarized in <http://bazaar-vcs.org/Roadmap>.
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We normally have one person acting as the release manager, who
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organizes development for the release and also actually makes the release
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tarball and posts announcements. It can be a different person from one
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Our usual process is that one week before release we will make a release
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branch from the trunk. We do one commit to that branch to change the
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version number to 'rc1', and advance the trunk version to 'dev' for the
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We then publish and announce this release candidate according to the
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process below. We then have a week of general testing of the rc,
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including some time for plugin authors to update their code for any
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Normally no changes will be made on the release branch unless serious bugs
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or regressions are found, and the release manager decides they should be
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merged in. After one week, the release branch's version number is updated
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and it's published as the final release. If regressions or serious
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problems are discovered after the final release we may make an additional
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point release from that branch.
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The process or timing can vary if that seems appropriate in a particular
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case but we try to release on a regular four week cycle.
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The net effect is that the code gets some extra testing before release,
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and the trunk is always open for general development.
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To start a new release cycle:
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#. Send mail to the list with the key dates, who will be the release
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manager, and the main themes or targetted bugs. Ask people to nominate
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objectives, or point out any high-risk things that are best done early,
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or that interact with other changes.
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#. Add a new "series" in Launchpad at <https://launchpad.net/bzr/+addseries>.
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There is one series for every *x.y* release.
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#. Add milestones to that series for the release candidate and the final
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release, and their expected dates.
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#. Deactivate old releases and their milestones.
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#. Update the version number in the ``bzr`` script, and the
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``bzrlib/__init__.py`` file.
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Weekly Metronome Mail
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of certain things, etc.
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Do users actually want this?
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Apparently yes, because it's often requested and often raised as a
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Would this confuse users?
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It shouldn't, because it's a fairly standard scheme.
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Won't it take more time to fix bugs in multiple places?
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It shouldn't, because we'll only do this when the stable bugfix seems
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economical. When we fix bugs today in both trunk and release branches
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it normally does not take much more time.
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What about bzr in Ubuntu LTS, with a five-year support life?
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Most bugs are either fixed within six months, or not fixed at all, or
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not very important, or fixed as part of a large rework of the code
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that would be too large to backport. However, if there are fixes that
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are especially desired in an old release and feasible to do, we can do
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them without making a general commitment.
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Will anyone test the beta releases?
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Probably yes, our most active users will run them, but if people would
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really rather not test them, forcing them is not helpful.
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Isn't this a step backwards to a slower, less-agile process?
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No, our trunk stays releasable, and we ship every month. We're just
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cutting out things that hold us back (continuous rather than episodic
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API stability; RCs every month) and giving users what they demand.
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How about calling the monthly releases "milestone" or "next" not "beta"?
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Those words are less scary but they also have less clear meanings.
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If this plan works, we'll expect to see the following changes. If they
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don't occur, we'll think again:
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* We see a distribution curve of users and bug reports across nightly, monthly
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and stable releases, indicating that each has value.
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* API changes are easier or safer to make during beta periods, without
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being held back by fears of compatibility or
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* The stable releases are actually stable and don't introduce regressions
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* Many bugs are fixed in stable branches, without developers feeling this
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* Distributions ship the stable releases in their stable releases and the
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bugfix releases in their bugfix releases.
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* Plugin authors follow this policy, making their own bugfix releases.
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After doing this for the 2.0 cycle (September 2009 through to early
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2010), it seems to be going well.
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Reviewing for the Stable Branch
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*******************************
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These are guidelines and can be interpreted case-by-case.
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* All changes to the stable branch should fix a bug, even if you would not
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normally file a bug for the change. The bug description should if at
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all possible explain how to manually verify the bug in a way that will
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fail before and pass after the change. (These are requirements for the
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* The change should be reasonably small and conservative.
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* Remember that the patch will be read during the SRU
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process and so keeping the patch small is useful even beyond keeping the
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logical changes small. Avoid doing mechanical bulk changes on the
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* Use particular care for things that may behave differently across
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platforms, encodings or locales. It's harder to thoroughly test these
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things before a release.
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* Generally speaking, just cleaning things up is not a sufficient reason
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to make changes to the stable branch. It has to actually fix a bug.
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* Changes to the stable branch should include tests as usual.
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* Don't change or remove existing APIs that might be used by plugins, even
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if they are underscore-prefixed. Adding APIs that are also being added
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to the trunk branch may make sense.
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* Keeping consistency with trunk is useful, but less important than
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keeping the stable branch stable.
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* (more items welcome)
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#. List thread "`[rfc] six-month stable release cycles`__", July 2009.
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.. __: https://lists.ubuntu.com/archives/bazaar/2009q3/060882.html
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Starting the release phase
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--------------------------
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When it's time to make the release candidate:
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#. We create a new pqm-controlled branch for this release series. The
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branch must be created by Robert Collins on the pqm server.
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This branch means that from the first release candidate onwards,
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general development continues on the trunk, and only
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specifically-targetted fixes go into the release.
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#. Register the branch at <https://launchpad.net/products/bzr/+addbranch>
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#. The revision at the start of that branch is `released
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<releasing.html>`_ as the first RC.
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doc/developers/cycle.txt
