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Using stacked branches
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======================
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If you are working on a project, and you have read access to whose
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public repository but do not have write access to it, using stacked
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branches to backup/publish your work onto the same host of the public
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repository might be an option for you.
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Other scenarios for stacked branch usage include experimental branches
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and code hosting sites. For these scenarios, stacked branches are
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ideal because of the benefits it provides.
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What is a stacked branch?
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A stacked branch is a branch that knows how to find revisions in
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another branch (the stacked-on branch). Stacked branches store just
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the unique revisions that are not in the stacked-on branch, making
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them faster to create and more storage efficient. In these respects,
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stacked branches are similar to shared repositories. However, stacked
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branches have additional benefits:
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A stacked branch is a branch that knows how to find revisions
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in another branch. Stacked branches store just the
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unique revisions, making them faster to create and more
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storage efficient. In these respects, stacked branches are
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similar to shared repositories. However, stacked branches have
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* The new branch can be in a completely different location to the
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branch being stacked on.
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repository can be physically readonly to developers committing to stacked
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These benefits make stacked branches ideal for various scenarios
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including experimental branches and code hosting sites.
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Creating a stacked branch
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-------------------------
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This creates a new branch at ``my-url`` that is stacked on ``reference-url``
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and only contains the revisions in the current branch that are not already
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in the branch at ``reference-url``. In particular, ``my-url`` and
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``reference-url`` can be on the same host, and the ``--stacked`` option
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can be used additionally to inform ``push`` to reference the
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revisions in ``reference-url``. For example::
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bzr push --stacked-on sftp://host/project --stacked sftp://host/user/stacked-branch
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This usage fits the scenario described in the Motivation section.
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.. The following text is hidden because bug 375013 breaks the example.
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When bug 375013 is fixed, we should unhide this text.
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- Andrew Bennetts, 10 March 2010
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.. If the local branch was created as a stacked branch, then you can
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.. use the ``--stacked`` option to ``push`` and the *stacked-on* location
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.. will be implicit. For example::
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.. bzr branch --stacked source-url my-dir
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.. bzr commit -m "fix bug"
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in the branch at ``reference-url``.
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If the local branch was created as a stacked branch, then you can
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use the ``--stacked`` option to ``push`` and the *stacked-on* location
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will be implicit. For example::
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bzr branch --stacked source-url my-dir
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bzr commit -m "fix bug"
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Limitations of stacked branches
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-------------------------------
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Currently, you cannot commit to a stacked branch, due to `bug 375013`_.
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.. _bug 375013: https://bugs.launchpad.net/bzr/+bug/375013
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The important thing to remember about a stacked branch is that the
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stacked-on branch needs to be available for almost all operations. This is
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not an issue when both branches are local or both branches are on the
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Similarly, because most of the history is stored in the stacked-on repository,
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operations like ``bzr log`` can be slower when the stacked-on repository is
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accessed via a network.
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Changing branch stacking
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------------------------