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Repositories store committed history: file texts, revisions, inventories,
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and graph relationships between them.
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Repositories can be configured to refer to a list of "fallback"
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repositories. If a particular revision is not present in the original
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repository, it refers the query to the fallbacks.
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Compression deltas don't span physical repository boundaries. So the
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first commit to a new empty repository with fallback repositories will
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store a full text of the inventory, and of every new file text.
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At runtime, repository stacking is actually configured by the branch, not
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the repository. So doing ``a_bzrdir.open_repository()``
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gets you just the single physical repository, while
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``a_bzrdir.open_branch().repository`` gets one configured with a stacking.
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Therefore to permanently change the fallback repository stored on disk,
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you must use ``Branch.set_stacked_on_url``.
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Changing away from an existing stacked on url will copy across any
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necessary history so that the repository remains usable.
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A repository opened from an hpss server is never stacked on the server
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side, because this could cause complexity or security problems with the
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server acting as a proxy for the client. Instead, the branch on the
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server exposes the stacked-on URL and the client can open that.
added
removed
doc/developers/overview.txt
