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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 This article is not all-inclusive and may become out of date quickly.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.

Features

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
9. ^ They can be automatically generated[1] and manually verified, but verification is not automatic
10. ^ Tags were introduced into Bazaar in version 0.15. Previous versions needed to use a plug in.
11. ^ darcs' patches each bear a unique identifier, it's pretty much impossible to merge twice the same patch in a repository
12. ^ Mercurial versions 0.9.4 and higher support symlinks.
13. ^ It could be done via user level hooks
14. ^ http://www.perforce.com/perforce/technotes/note007.html
15. ^ p4 supports unicode files. Files marked as unicode are converted to and from the user's local codepage unless that codepage cannot represent every character in the file. Therefore a unicode file with Japanese in it can not be checked out by a user not running a Japanese OS. Set the file type to text and p4 will not accept non ascii characters. Set the file to binary and perforce will not be able to do auto-merge, a required feature for source code. Therefore, p4 cannot be used for international software development.[2]
16. ^ StarTeam supports atomic commits as of version 2006
17. ^ Subversion can move a file and conserve its history, if and only if the target of the move is in the same Subversion repository as the source. Cross-repository moves require third-party tools such as svk. Also, a rename operation is actually a copy-with-history-and-delete sequence.
18. ^ A separate tool "svnmerge" provides merge tracking, see [3]. Merge tracking will be included in Subversion itself in the next major release, see [4]
19. ^ In Subversion, tags are a special case of the more generic "cheap copy" concept of Subversion. Per convention, a tag is a copy into a directory named "tags". Because of this, even tags are versioned. See [5] for more information. The reason for partial support in the table is because Subversion's emulation of tags in this manner does not meet the requirement that the tag name can be used in place of any revision identifier wherever the user may be required to enter one. This column would be meaningless if the definition were to be loosened enough to encompass Subversion's approach as every version control system supports branching and would therefore support tags as well.
20. ^ Uses subversion server
21. ^ Its possible to embed the action in a shell or Ant script.
22. ^ A merged is tracked by its workspace origin.

• Atomic commits refers to a guarantee that all commits are merged fully, or not at all.
• File renames describes whether a system allows files to be renamed while retaining their version history.
• Merge file renames describes whether a system can merge changes made to a file on one branch into the same file that has been renamed on another branch (or vice versa). If the same file has been renamed on both branches then there is a rename conflict that the user must resolve.
• Symbolic links describes whether a system allows revision control of symbolic links as with regular files. Versioning symbolic links is considered by some people a feature and some people a security breach (eg a symbolic link to /etc/passwd). Symbolic links are only supported on select platforms, depending on the software.
• Pre/post event hooks indicates the capability to trigger commands before or after an action, such as a commit, takes place.
• Signed revisions refers to integrated digital signing of revisions, in a format such as OpenPGP.
• Merge tracking describes whether a system remembers what changes have been merged between which branches and only merges the changes that are missing when merging one branch into another.
• End of line conversions describes whether a system can adapt the end of line characters for text files such that they match the end of line style for the operating system under which it is used. The granularity of control varies. Subversion, for example, can be configured to handle EOLs differently according to the file type, whereas Perforce converts all text files according a single, per-client setting.
• Tags indicates if meaningful names can be given to specific revisions.

User interfaces

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
9. ^ They can be automatically generated[6] and manually verified, but verification is not automatic
10. ^ Tags were introduced into Bazaar in version 0.15. Previous versions needed to use a plug in.
11. ^ darcs' patches each bear a unique identifier, it's pretty much impossible to merge twice the same patch in a repository
12. ^ Mercurial versions 0.9.4 and higher support symlinks.
13. ^ It could be done via user level hooks
14. ^ http://www.perforce.com/perforce/technotes/note007.html
15. ^ p4 supports unicode files. Files marked as unicode are converted to and from the user's local codepage unless that codepage cannot represent every character in the file. Therefore a unicode file with Japanese in it can not be checked out by a user not running a Japanese OS. Set the file type to text and p4 will not accept non ascii characters. Set the file to binary and perforce will not be able to do auto-merge, a required feature for source code. Therefore, p4 cannot be used for international software development.[7]
16. ^ StarTeam supports atomic commits as of version 2006
17. ^ Subversion can move a file and conserve its history, if and only if the target of the move is in the same Subversion repository as the source. Cross-repository moves require third-party tools such as svk. Also, a rename operation is actually a copy-with-history-and-delete sequence.
18. ^ A separate tool "svnmerge" provides merge tracking, see [8]. Merge tracking will be included in Subversion itself in the next major release, see [9]
19. ^ In Subversion, tags are a special case of the more generic "cheap copy" concept of Subversion. Per convention, a tag is a copy into a directory named "tags". Because of this, even tags are versioned. See [10] for more information. The reason for partial support in the table is because Subversion's emulation of tags in this manner does not meet the requirement that the tag name can be used in place of any revision identifier wherever the user may be required to enter one. This column would be meaningless if the definition were to be loosened enough to encompass Subversion's approach as every version control system supports branching and would therefore support tags as well.
20. ^ Uses subversion server
21. ^ Its possible to embed the action in a shell or Ant script.
22. ^ A merged is tracked by its workspace origin.
23. ^ hgweb for single-repository access and hgwebdir for multiple repository access from a single HTTP address
24. ^ Any OS that support a Java Virtual Machine 1.5

History and adoption

• Notable users is a list of well known projects using the software as their primary revision control system, excluding the software itself, followed by a link to a full list if available.
• History briefly describes the software's origins and development.

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
9. ^ They can be automatically generated[11] and manually verified, but verification is not automatic
10. ^ Tags were introduced into Bazaar in version 0.15. Previous versions needed to use a plug in.
11. ^ darcs' patches each bear a unique identifier, it's pretty much impossible to merge twice the same patch in a repository
12. ^ Mercurial versions 0.9.4 and higher support symlinks.
13. ^ It could be done via user level hooks
14. ^ http://www.perforce.com/perforce/technotes/note007.html
15. ^ p4 supports unicode files. Files marked as unicode are converted to and from the user's local codepage unless that codepage cannot represent every character in the file. Therefore a unicode file with Japanese in it can not be checked out by a user not running a Japanese OS. Set the file type to text and p4 will not accept non ascii characters. Set the file to binary and perforce will not be able to do auto-merge, a required feature for source code. Therefore, p4 cannot be used for international software development.[12]
16. ^ StarTeam supports atomic commits as of version 2006
17. ^ Subversion can move a file and conserve its history, if and only if the target of the move is in the same Subversion repository as the source. Cross-repository moves require third-party tools such as svk. Also, a rename operation is actually a copy-with-history-and-delete sequence.
18. ^ A separate tool "svnmerge" provides merge tracking, see [13]. Merge tracking will be included in Subversion itself in the next major release, see [14]
19. ^ In Subversion, tags are a special case of the more generic "cheap copy" concept of Subversion. Per convention, a tag is a copy into a directory named "tags". Because of this, even tags are versioned. See [15] for more information. The reason for partial support in the table is because Subversion's emulation of tags in this manner does not meet the requirement that the tag name can be used in place of any revision identifier wherever the user may be required to enter one. This column would be meaningless if the definition were to be loosened enough to encompass Subversion's approach as every version control system supports branching and would therefore support tags as well.
20. ^ Uses subversion server
21. ^ Its possible to embed the action in a shell or Ant script.
22. ^ A merged is tracked by its workspace origin.
23. ^ hgweb for single-repository access and hgwebdir for multiple repository access from a single HTTP address
24. ^ Any OS that support a Java Virtual Machine 1.5
25. ^ Towards A Better SCM: Revlogs and Mercurial, presented by Matt Mackall to the Ottawa Linux Symposium, July 2006

See also

• List of revision control software

External links

• Comments on Open Source Software / Free Software SCM systems by David A. Wheeler
• Quick Reference Guide to Free Software Decentralized Revision Control Systems by Zooko
• Comparison of commercial Version Control Systems, from the creators of Code Co-op
• Version Control System Comparison from better-scm.berlios.de
• Evaluation of distributed source code management solutions for OpenSolaris by Sun
• Analysis of alternatives to CVS for Freedesktop.org by Keith Packard

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List of revision control software
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