On 08/05/2012 06:56 AM, Junio C Hamano wrote:
The "alternates" mechanism [...]
The UI for this mechanism however has some room for improvement, and
we may want to start improving it for the next release after the
upcoming Git 1.7.12 (or even Git 2.0 if the change is a large one
that may be backward incompatible but gives us a vast improvement).
Here are some random thoughts as a discussion starter. [...]
- Make the distinction between a regular repository and an object
store that is meant to be used for object sharing stronger.
Perhaps a configuration item "core.objectstore = readonly" can
be introduced, and we forbid "clone -s" from pointing at a
repository without such a configuration. We also forbid object
pruning operations such as "gc" and "repack" from being run in
a repository marked as such.
Must the repository necessarily be "readonly"? It seems that it would
be permissible to push new objects to such a repository; just not to
delete existing objects. Thus maybe another term would be better to
describe such a repository, like "appendonly" or "noprune" or even
something more abstract like "donor".
I have some other crazy ideas for making the concept even more powerful:
* Support remote alternate repositories. Local repository obtains
missing objects from the remote as needed. This would probably be
insanely inefficient without also supporting...
* Lazy copying of "borrowed" objects to the local repository. Any
object fetched from the alternate object store is copied to the local
Together, I think that these two features would give fully-functional
Such alternates could even be chained together: for example, keep a
single local lazy clone of the upstream repository somewhere on your
site or on your computer, and use that as read-through cache for other
* To help manage local disk space, allow intelligent curation of the
objects kept in the local store when they are also available in the
alternate. The criteria for what to keep could be things like
"revisions with depth <= 20 on branches X, Y/*, and Z"; "objects that
have been accessed within the last 3 months", "all tag objects
refs/tags/release-*". It should be possible to cull objects not meeting
the criteria with or without actively fetching all objects meeting the
criteria. Probably the criteria would be stored in the configuration to
be reused (and perhaps run as part of "git gc").
This would cure a lot of "storing big, non-deltaable files" pain because
big blobs could be stored on a central server without multiplying the
size of every clone.
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