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What's the difference between `git show branch:file | diff -u - file` vs `git diff branch file`?

From
Marat Radchenko <marat@slonopotamus.org>
Date
Aug 23, 2011, 07:25 UTC
Message-ID
<loom.20110823T091132-107@post.gmane.org>
$ time git show branch:file | diff -u - file > /dev/null

real 0m0.003s user 0m0.000s sys 0m0.000s

$ time git diff branch -- file > /dev/null

real 0m31.442s user 0m31.040s sys 0m0.380s

What does git diff do so it takes that much time? And is there any flag to git diff so that it will work as fast as show + diff? I thought these two are equivalent but from run time it is obvious that they aren't.

gprof output: http://slonopotamus.org/git-diff/git-diff-branch.gprof.txt
Next: Michael J Gruber
Message 1 of 56 in “What's the difference between `git show branch:file | diff -u - file` vs `git diff branch file`?”
  1. Marat RadchenkoAug 23, 2011
  2. Michael J GruberAug 23, 2011
  3. Marat RadchenkoAug 23, 2011
  4. Michael WittenAug 23, 2011
  5. Michael J GruberAug 23, 2011
  6. Marat RadchenkoAug 23, 2011
  7. Junio C HamanoAug 23, 2011
  8. Marat RadchenkoAug 23, 2011
  9. Michael J GruberAug 23, 2011
  10. Marat RadchenkoAug 25, 2011
  11. Junio C HamanoAug 25, 2011
  12. Marat RadchenkoAug 26, 2011
  13. Nguyen Thai Ngoc DuyAug 29, 2011
  14. Marat RadchenkoAug 29, 2011
  15. Nguyen Thai Ngoc DuyAug 29, 2011
  16. Junio C HamanoAug 29, 2011
  17. Junio C HamanoAug 29, 2011
  18. Junio C HamanoAug 29, 2011
  19. Junio C HamanoAug 29, 2011
  20. 0/3 Un-pessimize "diff-index $commit -- $pathspec"Junio C Hamano, Aug 29, 2011
  21. 1/3 traverse_trees(): allow pruning with pathspecJunio C Hamano, Aug 29, 2011
  22. Nguyen Thai Ngoc DuyAug 30, 2011
  23. Junio C HamanoAug 30, 2011
  24. Nguyen Thai Ngoc DuyAug 31, 2011
  25. Michael HaggertyOct 9, 2011
  26. Nguyen Thai Ngoc DuyOct 9, 2011
  27. Michael HaggertyOct 10, 2011
  28. 2/3 unpack-trees: allow pruning with pathspecJunio C Hamano, Aug 29, 2011
  29. Nguyen Thai Ngoc DuyAug 30, 2011
  30. Junio C HamanoAug 30, 2011
  31. David Michael BarrAug 30, 2011
  32. 3/3 diff-index: pass pathspec down to unpack-trees machineryJunio C Hamano, Aug 29, 2011
  33. Jonathan NiederJan 11, 2012
  34. Junio C HamanoJan 11, 2012
  35. Nguyen Thai Ngoc DuyJan 11, 2012
  36. Nguyen Thai Ngoc DuyJan 11, 2012
  37. Junio C HamanoJan 11, 2012
  38. tree_entry_interesting: make recursive mode defaultNguyễn Thái Ngọc Duy, Jan 12, 2012
  39. Junio C HamanoJan 12, 2012
  40. Nguyen Thai Ngoc DuyJan 12, 2012
  41. 1/2 Document limited recursion pathspec matching with wildcardsNguyễn Thái Ngọc Duy, Jan 14, 2012
  42. 2/2 tree_entry_interesting: make recursive mode defaultNguyễn Thái Ngọc Duy, Jan 14, 2012
  43. Junio C HamanoJan 15, 2012
  44. Nguyen Thai Ngoc DuyJan 15, 2012
  45. Junio C HamanoJan 16, 2012
  46. Nguyen Thai Ngoc DuyJan 18, 2012
  47. Junio C HamanoJan 15, 2012
  48. Nguyen Thai Ngoc DuyJan 15, 2012
  49. Linus TorvaldsAug 29, 2011
  50. Junio C HamanoAug 29, 2011
  51. Linus TorvaldsAug 29, 2011
  52. Junio C HamanoAug 29, 2011
  53. Marat RadchenkoAug 30, 2011
  54. Junio C HamanoAug 31, 2011
  55. Michael J GruberAug 30, 2011
  56. Junio C HamanoAug 30, 2011

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