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==============================
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Development repository formats
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==============================
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Using development repository formats
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====================================
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We believe that we can continue to gain substantial performance benefits
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by altering the repository storage in bzr. The more feedback we can get
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on the changes during the development process the better.
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To make it possible to get more feedback we are going to expose the
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current development formats to the users of our development trunk
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'bzr.dev'. The technical details of the individual formats are at the
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The current development format will be called 'development'. Each time
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the development format changes, the prior development format will be
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renamed to e.g. 'development0', 'development1' etc.
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When a release of bzr is done, all the older numbered development
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formats will be removed from 'bzr.dev', so we will not be carrying the
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code for them around indefinately.
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Support for upgrade and migration
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---------------------------------
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The preservation and renaming policy makes it quite safe for users to
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test out development formats (though we cannot guarantee bugs of course
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- it is development code):
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- users of a given development format can always get back onto regular
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formats by switching to the next bzr released version which is
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guaranteed to be able to upgrade from that development format.
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- users that routinely use bzr.dev should upgrade to the most recent
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development version available before pulling in bzr.dev changes
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around release time, as that is when old format cleanups will occur.
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We cannot guarantee backwards compatability though, because some of the
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planned work may be 'upgrade only'. Please see ``bzr help formats`` for
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the text of the 'development' format which will indicate its
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compatability with other formats if you need to interoperate with
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users or services that do not have bzr.dev.
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Before converting to a development format
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-----------------------------------------
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Run a ``bzr check`` with the version of bzr that you will be using.
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``bzr check`` gets updated as we find new things that are inconsistent
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with existing repositories. While only a small number of repositories
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are likely to have any given error, it is best to check just in case.
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If ``bzr check`` reports a problem, run this command::
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Note that reconcile can take many hours, particularly if you are
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reconciling one of the 'knit' or 'dirstate' format repositories. If you
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have such a repository, consider upgrading it to 'pack-0.92' first,
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which will perform reconcile significantly faster.
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Creating a new development format branch
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----------------------------------------
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If you're starting a project from scratch, it's easy to make it a
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``development`` one. Here's how::
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bzr init --development
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bzr commit -m "initial import"
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In other words, use the normal sequence of commands but add the
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``--development`` option to the ``init`` command.
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Creating a new development format repository
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--------------------------------------------
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If you're starting a project from scratch and wish to use a shared repository
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for branches, you can make it a ``development`` repository like this::
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bzr init-repo --development .
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bzr commit -m "initial import"
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In other words, use the normal sequence of commands but add the
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``--development`` option to the ``init-repo`` command.
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Upgrading an existing branch or repository to development
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---------------------------------------------------------
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If you have an existing branch and wish to migrate it to
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a ``development`` format, use the ``upgrade`` command like this::
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bzr upgrade --development path-to-my-branch
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If you are using a shared repository, run::
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bzr upgrade --development ROOT_OF_REPOSITORY
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to upgrade the history database. Note that this will not
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alter the branch format of each branch, so
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you will need to also upgrade each branch individually
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if you are upgrading from an old (e.g. < 0.17) bzr.
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More modern bzr's will already have the branch format at
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our latest branch format which adds support for tags.
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Starting a new development format branch from one in an older format
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--------------------------------------------------------------------
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This can be done in one of several ways:
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1. Create a new branch and pull into it
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2. Create a standalone branch and upgrade its format
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3. Create a knitpack shared repository and branch into it
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Here are the commands for using the ``pull`` approach::
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bzr init --development my-new-branch
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bzr pull my-source-branch
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Here are the commands for using the ``upgrade`` approach::
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bzr branch my-source-branch my-new-branch
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bzr upgrade --development .
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Here are the commands for the shared repository approach::
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bzr init-repo --development .
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bzr branch my-source-branch my-new-branch
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As a reminder, any of the above approaches can fail if the source branch
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has inconsistent data within it and hasn't been reconciled yet. Please
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be sure to check that before reporting problems.
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Develoment formats for bzr-svn users
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------------------------------------
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If you are using ``bzr-svn`` or are testing the prototype subtree support,
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you can still use and assist in testing the development formats. The
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commands to use are identical to the ones given above except that the
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name of the format to use is ``development-subtree``.
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**WARNING**: Note that bzr only supports one-way conversion **to** the
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subtree format ``development-subtree``. Once you are using
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``development-subtree`` you cannot pull or merge back into a regular
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format such as ``pack-0.92``, ``development`` etc.
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The ``development-subtree`` format is required for the bzr-svn
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plug-in but should otherwise not be used until the subtree feature is
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If you need any help or encounter any problems, please contact the developers
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via the usual ways, i.e. chat to us on IRC or send a message to our mailing
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list. See http://bazaar-vcs.org/BzrSupport for contact details.
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When to create a new development format
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---------------------------------------
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Whenever a code change will result in incorrect behaviour with existing
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``development`` repositories. Changes in push/pull/init/commit/merge
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have all been known to do this in the past.
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How to create a new development format
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--------------------------------------
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1. Register two new formats with the next available sequence number.
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e.g. ``development1`` and ``development1-subtree``. (You can see the
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current development format for an example.
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* Use your new development repository/branch/tree classes
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* Have really bare bones help - something like 'changes X to be Y
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see ...developers/development-repo.html'
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* Be hidden and experimental.
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2. Change the repository class (or branch or tree) in the
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``development`` and ``development-subtree`` formats to point to the
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new class you are creating.
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3. Add a new development format (and tests!). Repository formats are in
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``bzrlib.repofmt``. You probably want to reproduce the current
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development format from ``bzrlib.repofmt.pack_repo`` with just new
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disk format strings, ``_get_matching_bzrdir`` and help.
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4. Register your development format with the various registries. At the
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moment you need to update:
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1. ``bzrlib/bzrdir.py`` to register the WT/Branch/Repository
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2. ``bzrlib/workingtree.py``, ``bzrlib/branch.py``,
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``bzrlib/repository.py``, each one maintains a direct list of
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their respective formats.
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3. For repositories, you also need to update the InterKnit1and2
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class. This is responsible for converting between rich-root and
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non-rich-root repositories.
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4. For repositories based on KnitPackRepository, you need to update
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``bzrlib/tests/test_pack_repository.py`` to add the class to the
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5. Alter any other things that do class based tests. The easiest way
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to find these is a grep for Development in bzrlib - and please
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refactor as you find these to reduce the relevance this step has,
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as it should not need to exist.
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6. Now subclass/create from scratch/whatever the live object code you
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need to change to introduce your new format. Keep in mind that
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eventually it will become the default format, so please don't keep
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subclassing the last releases code, rather consider making the last
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releases code a subclass of your new code (if there is a lot in
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common) so that we can eventually remove that format once it becomes
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ancient (or relegate it to a plugin).
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7. Once you have made the changes that required a new disk format, you
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should submit the resulting branch to be merged. Other changes - to
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take advantage of whatever new feature you have added - should be
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sent in separately, because the disk level changes are a contention
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point between multiple developers.
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Not currently available, as our development formats are all rich root or
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development-rich-root
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---------------------
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Currently an alias for Development6Subtree
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Currently an alias for Development6Subtree
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Development6RichRoot[Subtree]
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-----------------------------
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These formats use the new groupcompress delta compress and a CHK(Content
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Hash Key) based inventory store which is much faster at incremental
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operations than the prior XML based store.
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*Note* Converting from a non-rich-root to a rich-root format is a
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one-way upgrade, and you cannot merge back afterwards: using this format
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for everyday use is likely to cause all developers of a project to
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upgrade to a rich-root format themselves. This is fine, as bzr is moving
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to make rich-root formats the default and to get all users to upgrade,
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but we have not finalised the migration process, and until we do do not
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recomment that casual users upgrade. Users of bzr-svn are already using
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rich-root formats and can test with this with impunity.
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doc/developers/development-repo.txt
