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Comparison of revision control software

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The following tables compare general and technical information for notable revision control and software configuration management (SCM) software. This article is not all-inclusive and may become out of date quickly.

General information

1. ^ Although Bazaar is a distributed version control system it can also be used in a centralized manner using lock step development and checkouts.
2. ^ In ClearCase, a trigger may be set to allow for the lock model, and this is done at many sites. However, ClearCase development usually takes place on private branches where each developer is given their own branch, so the lock vs. merge concurrency model doesn't matter as much. Code is merged back to the main branch once the developer is ready to deliver their code to the project.
3. ^ SVK allows Subversion to have distributed branches.
4. ^ In Subversion, a file attribute enables the lock model on per-file basis. This file attribute can be set automatically using file name wildcard expressions.

• Repository model describes the relationship between various copies of the source code repository. In a client-server model, users access a master repository via a client; typically, their local machines hold only a working copy of a project tree. Changes in one working copy must be committed to the master repository before they are propagated to other users. In a distributed model, repositories act as peers, and users typically have a local repository with version history available, in addition to their working copies.
• Concurrency model describes how changes to the working copy are managed to prevent simultaneous edits from causing nonsensical data in the repository. In a lock model, changes are disallowed until the user requests and receives an exclusive lock on the file from the master repository. In a merge model, users may freely edit files, but are informed of possible conflicts upon checking their changes into the repository, whereupon the version control system may merge changes on both sides, or let the user decide when conflicts arise. Note that distributed version control almost always implies a merge concurrency model.

Technical information

1. ^ Although Bazaar is a distributed version control system it can also be used in a centralized manner using lock step development and checkouts.
2. ^ In ClearCase, a trigger may be set to allow for the lock model, and this is done at many sites. However, ClearCase development usually takes place on private branches where each developer is given their own branch, so the lock vs. merge concurrency model doesn't matter as much. Code is merged back to the main branch once the developer is ready to deliver their code to the project.
3. ^ SVK allows Subversion to have distributed branches.
4. ^ In Subversion, a file attribute enables the lock model on per-file basis. This file attribute can be set automatically using file name wildcard expressions.
5. ^ A Bazaar bundle is a summary diff, with sufficient extra information to preserve history.
6. ^ Mercurial 0.5b vs git. overview of performance/scalability.
7. ^ A Monotone's revisions represent changesets and its manifests represent snapshots, each revision is linked to some manifest. But manifests are legacy constructs, they aren't kept in the database anymore and reconstructed on the fly if needed. The real work now happen in rosters which are hybrid snapshot/changeset structures.
8. ^ ^{a b} ssh tunneling is optional

• History model describes the form in which changes are stored in the repository. For example, when a change is committed, a system could store a copy of the tree before and after the change (snapshot), or it might instead store a copy of the tree before the change and a changeset representing the changes.
• Revision IDs are used internally to identify specific versions of files in the repository. Systems may use pseudorandom identifiers, content hashes of revisions, or filenames with sequential version numbers (namespace).
• Repo. size describes how the repository grows as changes are committed. O(patch) means that it grows as the size of the patches between revisions, while O(revisions) means that it grows as the size of each revision checked in.
• Network protocols lists the protocols used for synchronization of changes.

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