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Darcs is a database for managing patches. Nothing in Git inherently cares about patches. To a first approximation it's a database for managing full snapshots of

by avar 8y ago

Darcs is a database for managing patches. Nothing in Git inherently cares about patches. To a first approximation it's a database for managing full snapshots of trees of files.

gmueckl 8y ago
Git only needs lists of files because it needs entry points into its lists of patch fragments that make up the file and to assign file names to them. Other than that, a changeset is just another name for a patch that can be added, altered, rewritten or removed. That makes git a patch database in my book. Darcs feels more like a research project to me. The developers try to find a theoretical foundation in which they can base a VCS, but they have not managed to make their theory work with the level of perfection that they want. But if they eventually get it right, it will probably have the provably best text-based merge tool possible.
- avar 8y ago
  This is not how Git's data model works. You may be thinking of delta-compression which during "git gc" and purely as an optimization step does delta-compression across content in the repository. But that's purely an optimization that has nothing to do with the intrinsic data model. There's no point at which the patch output you see with "git diff/show" is actually stored as-is in Git. It's computed on-the-fly. This separates Git from many other SCMs where patches or other deltas are permanently stored at the time of commit in a way that can't modified afterwards. The distinction matters because those systems generally have storage that doesn't compress as well, since they need to compute and store a diff at the time, whereas a system like Git can keep finding better delta candidates as history progresses. This goes all the way back to the likes of RCS. The Subversion FSFS backend also works like this, and I believe Mercurial to some extent, and certainly Darcs since storing a history of patches is what it's for.

by avar 8y ago

Darcs is a database for managing patches. Nothing in Git inherently cares about patches. To a first approximation it's a database for managing full snapshots of trees of files.

gmueckl 8y ago

Git only needs lists of files because it needs entry points into its lists of patch fragments that make up the file and to assign file names to them. Other than that, a changeset is just another name for a patch that can be added, altered, rewritten or removed. That makes git a patch database in my book. Darcs feels more like a research project to me. The developers try to find a theoretical foundation in which they can base a VCS, but they have not managed to make their theory work with the level of perfection that they want. But if they eventually get it right, it will probably have the provably best text-based merge tool possible.

avar 8y ago
This is not how Git's data model works. You may be thinking of delta-compression which during "git gc" and purely as an optimization step does delta-compression across content in the repository. But that's purely an optimization that has nothing to do with the intrinsic data model. There's no point at which the patch output you see with "git diff/show" is actually stored as-is in Git. It's computed on-the-fly. This separates Git from many other SCMs where patches or other deltas are permanently stored at the time of commit in a way that can't modified afterwards. The distinction matters because those systems generally have storage that doesn't compress as well, since they need to compute and store a diff at the time, whereas a system like Git can keep finding better delta candidates as history progresses. This goes all the way back to the likes of RCS. The Subversion FSFS backend also works like this, and I believe Mercurial to some extent, and certainly Darcs since storing a history of patches is what it's for.