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→‎2009-06-16: prototype finished - thoughts about datastore rewrite
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Created [http://git.sugarlabs.org/projects/versionsupport-project/repos/mainline/trees/master/backends git VCS backend]. There's
 
Created [http://git.sugarlabs.org/projects/versionsupport-project/repos/mainline/trees/master/backends git VCS backend]. There's
 
room for performance improvement and code simplification, but it's fully working, including getBranches() and getVersions().
 
room for performance improvement and code simplification, but it's fully working, including getBranches() and getVersions().
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Got a working prototype
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([http://git.sugarlabs.org/projects/sugar/repos/versionsupport sugar],
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[http://git.sugarlabs.org/projects/sugar/repos/versionsupport sugar-datastore],
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[http://git.sugarlabs.org/projects/sugar/repos/versionsupport sugar-toolkit]). It treats each version as a separate object, unrelated to the others - so no topology, no branches. But it's working and the basic user experience (details view allows selecting old versions, changing metadata and resuming them) is there.
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The API has been changed to add a version_id in parallel to object_id. This seemed cleanest, but also needs invasive code changes (though most activities will continue to work as-is - the framework (sugar-toolkit) usually handles save/resume for them). Breaking the API is almost unavoidable - see [http://git.sugarlabs.org/projects/versionsupport-project/repos/mainline/blobs/master/API-choosing-notes.txt my API choosing notes] for details. But I noticed that in most cases we want to identify a single version, so we could alter the Python side of the API to do that by default, in a single parameter - e.g. by passing a tuple (object_id, version_id) - instead of always passing around two separate parameters. The few places where we want to identify all versions of an object, we can do that explicitly.
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And as I'm breaking API already, I'm thinking about tweaking it with regard to (a)synchronous operation - the code suggests it's currently half-synchronous, half asynchronous. For UI responsiveness, the "heavy" operations should be done without blocking the activity. So basically the activity provides new content, data store accepts it in a queue and adds it to the VCS backend after the activity has regained control (partially this is already being done today - see the optimizer code). Hardlinking and crashes (power loss) need to be considered carefully.
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Also need to choose how to save metadata - use the current journal format extended to save a separate entry per '''version''' (as in the prototype), but store the data in a VCS per '''object'''. Or move to a standard database like sqlite. As for data, crash recovery needs to be carefully considered.
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