How does git detect similar files, for its rename detection?

by

Git tracks file contents, not filenames. So renaming a file without changing its content is easy for git to detect. (Git does not track, but performs detection; using git mv or git rm and git add is effectively the same.)

When a file is added to the repository, the filename is in the tree object. The actual file contents are added as a binary large object (blob) in the repository. Git will not add another blob for additional files that contain the same content. In fact, Git cannot as the content is stored in the filesystem with first two characters of the hash being the directory name and the rest being the name of file within it. So to detect renames is a matter of comparing hashes.

To detect small changes to a renamed file, Git uses certain algorithms and a threshold limit to see if this is a rename. For example, have a look at the -M flag for git diff. There are also configuration values such as merge.renameLimit (the number of files to consider when performing rename detection during a merge).

To understand how git treats similar files (i.e., what file transformations are considered as renames), explore the configuration options and flags available, as mentioned above. You need not be considered with the how. To understand how git actually accomplishes these tasks, look at the algorithms for finding differences in text, and read the git source code.

Algorithms are applied only for diff, merge, and log purposes — they do not affect how git stores them. Any small change in file content means a new object is added for it. There is no delta or diff happening at that level. Of course, later, the objects might be packed where deltas are stored in packfiles, but that is not related to the rename detection.

More Related Contents:

  1. Can Git hook scripts be managed along with the repository?
  2. How do I “un-revert” a reverted Git commit?
  3. Having a hard time understanding git-fetch
  4. Sparse checkout in Git 1.7.0?
  5. How can I view a git log of just one user’s commits?
  6. Is it possible to create a remote repo on GitHub from the CLI without opening browser?
  7. git push –force-with-lease vs. –force
  8. Can I make git recognize a UTF-16 file as text?
  9. What’s the difference between Git Revert, Checkout and Reset?
  10. Configuring diff tool with .gitconfig
  11. How to export revision history from mercurial or git to cvs?
  12. Windows git “warning: LF will be replaced by CRLF”, is that warning tail backward?
  13. git stash and apply
  14. How do you get git to always pull from a specific branch?
  15. Git Cherry-pick vs Merge Workflow
  16. Is there a way to lock a branch in GIT
  17. What are the practical consequences of rewriting Git history?
  18. What is git-rerere and how does it work?
  19. ‘git pull origin mybranch’ leaves local mybranch N commits ahead of origin. Why?
  20. A way to restrict Git branch access?
  21. How do I react to new tags in git hooks?
  22. What are the “loose objects” that the Git GUI refers to?
  23. Is there a way to tell git to only include certain files instead of ignoring certain files?
  24. How to point Go module dependency in go.mod to a latest commit in a repo?
  25. Rolling back a remote Git repository
  26. Is it possible to pull just one file in Git?
  27. Using a Jenkins pipeline to checkout multiple git repos into same job
  28. git ignore all files of a certain type, except those in a specific subfolder
  29. How to delete the last n commits on Github and locally?
  30. How do I execute a Git command without being in the repository?

Leave a Comment