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Re: remove_duplicates() in builtin/fetch-pack.c is O(N^2)

From
Jeff King <peff@peff.net>
Date
May 22, 2012, 00:07 UTC
Message-ID
<20120522000747.GA8920@sigill.intra.peff.net>
In-Reply-To
<20120521235219.GA5589@sigill.intra.peff.net>
On Mon, May 21, 2012 at 07:52:19PM -0400, Jeff King wrote:
Show 5 quoted lines
> Try doing "git fetch . refs/*:refs/*" in a repository with a large
> number of refs (e.g., 400K). With git v1.7.10, this takes about 9.5s on
> my machine. But using the version of git in "next" takes about 16.5s.
> Bisection points to your 432ad41 (refs: store references hierarchically,
> 2012-04-10). Perf shows sort_ref_dir and msort_with_tmp as hot spots.
A few more facts:
  - I usually compile with -O0 because I am debugging so frequently.
    With -O3, those numbers become 6.0s and 11.2s, respectively. Much
    faster, but there is still a performance regression.
  - Almost all of the refs are packed. IIRC, the packed-refs file should
    already be sorted. I wonder if we did not bother double-checking
    that before your patch, and now we do. That could explain the
    difference.
  - I don't compile with INTERNAL_QSORT. So mentioning msort_with_tmp is
    slightly confusing, as it is actually the version from libc, not
    ours IOW, it is really just qsort. But the primary culprit remains
    sort_ref_dir.
-Peff
Previous: Jeff KingNext: Michael Haggerty
Message 16 of 46 in “remove_duplicates() in builtin/fetch-pack.c is O(N^2)”
  1. Michael HaggertyMay 21, 2012
  2. Junio C HamanoMay 21, 2012
  3. demerphqMay 21, 2012
  4. Jeff KingMay 21, 2012
  5. Jeff KingMay 21, 2012
  6. 1/5 fetch-pack: sort incoming headsJeff King, May 21, 2012
  7. Junio C HamanoMay 22, 2012
  8. Jeff KingMay 22, 2012
  9. Jeff KingMay 24, 2012
  10. 2/5 fetch-pack: avoid quadratic behavior in remove_duplicatesJeff King, May 21, 2012
  11. 3/5 add sorting infrastructure for list refsJeff King, May 21, 2012
  12. 4/5 fetch-pack: sort the list of incoming refsJeff King, May 21, 2012
  13. 5/5 fetch-pack: avoid quadratic loop in filter_refsJeff King, May 21, 2012
  14. Junio C HamanoMay 22, 2012
  15. Jeff KingMay 21, 2012
  16. Jeff KingMay 22, 2012
  17. Michael HaggertyMay 22, 2012
  18. Jeff KingMay 22, 2012
  19. Michael HaggertyMay 22, 2012
  20. Jeff KingMay 22, 2012
  21. Michael HaggertyMay 22, 2012
  22. Jeff KingMay 22, 2012
  23. Michael HaggertyMay 24, 2012
  24. Martin FickMay 25, 2012
  25. Jeff KingMay 25, 2012
  26. Martin FickMay 25, 2012
  27. Jeff KingMay 25, 2012
  28. Martin FickMay 25, 2012
  29. Jeff KingMay 25, 2012
  30. Nguyen Thai Ngoc DuyMay 22, 2012
  31. Michael HaggertyMay 22, 2012
  32. Jeff KingMay 22, 2012
  33. Junio C HamanoMay 22, 2012
  34. Jeff KingMay 22, 2012
  35. Michael HaggertyMay 24, 2012
  36. Nguyen Thai Ngoc DuyMay 23, 2012
  37. Junio C HamanoMay 22, 2012
  38. Martin FickMay 21, 2012
  39. Jeff KingMay 21, 2012
  40. Junio C HamanoMay 21, 2012
  41. Jeff KingMay 21, 2012
  42. Martin FickMay 22, 2012
  43. Jeff KingMay 22, 2012
  44. Martin FickMay 22, 2012
  45. Junio C HamanoMay 22, 2012
  46. Martin FickMay 23, 2012

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