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Re: [PATCH 4/6] introduce a commit metapack

From
Duy Nguyen <pclouds@gmail.com>
Date
Mar 17, 2013, 13:21 UTC
Message-ID
<CACsJy8CPXFhUYz2f1wuxJvqwknJr5VFNFrs3b_4pS14cxf=3Wg@mail.gmail.com>
In-Reply-To
<20130131110656.GA28093@lanh>
On Thu, Jan 31, 2013 at 6:06 PM, Duy Nguyen <pclouds@gmail.com> wrote:
Show 14 quoted lines
> On Wed, Jan 30, 2013 at 09:16:29PM +0700, Duy Nguyen wrote:
>> Perhaps we could store abbrev sha-1 instead of full sha-1. Nice
>> space/time trade-off.
>
> Following the on-disk format experiment yesterday, I changed the
> format to:
>
>  - a list a _short_ SHA-1 of cached commits
> ..
>
> The length of SHA-1 is chosen to be able to unambiguously identify any
> cached commits. Full SHA-1 check is done after to catch false
> positives. For linux-2.6, SHA-1 length is 6 bytes, git and many
> moderate-sized projects are 4 bytes.

And if we are going to create index v3, the same trick could be used for the sha-1 table in the index. We use the short sha-1 table for binary search and put the rest of sha-1 in a following table (just like file offset table). The advantage is a denser search space, about 1/4-1/3 the size of full sha-1 table.

-- 
Duy
Previous: Jeff KingNext: Jeff King
Message 33 of 43 in “commit caching”
  1. 0/6 commit cachingJeff King, Jan 29, 2013
  2. 1/6 csum-file: make sha1write const-correctJeff King, Jan 29, 2013
  3. 2/6 strbuf: add string-chomping functionsJeff King, Jan 29, 2013
  4. Michael HaggertyJan 29, 2013
  5. Jeff KingJan 29, 2013
  6. Michael HaggertyJan 30, 2013
  7. 3/6 introduce pack metadata cache filesJeff King, Jan 29, 2013
  8. Junio C HamanoJan 29, 2013
  9. Jeff KingJan 30, 2013
  10. Duy NguyenJan 30, 2013
  11. Jeff KingJan 30, 2013
  12. 4/6 introduce a commit metapackJeff King, Jan 29, 2013
  13. Michael HaggertyJan 29, 2013
  14. Jeff KingJan 29, 2013
  15. Junio C HamanoJan 29, 2013
  16. Junio C HamanoJan 29, 2013
  17. Jeff KingJan 30, 2013
  18. Junio C HamanoJan 30, 2013
  19. Jeff KingFeb 1, 2013
  20. Junio C HamanoJan 30, 2013
  21. Shawn PearceJan 31, 2013
  22. Jeff KingFeb 1, 2013
  23. Junio C HamanoFeb 2, 2013
  24. Jeff KingJan 30, 2013
  25. Duy NguyenJan 30, 2013
  26. Jeff KingJan 30, 2013
  27. Duy NguyenJan 30, 2013
  28. Duy NguyenJan 30, 2013
  29. Duy NguyenJan 31, 2013
  30. Jeff KingFeb 1, 2013
  31. Duy NguyenFeb 2, 2013
  32. Jeff KingFeb 1, 2013
  33. Duy NguyenMar 17, 2013
  34. Jeff KingMar 18, 2013
  35. Jeff KingFeb 1, 2013
  36. 5/6 add git-metapack commandJeff King, Jan 29, 2013
  37. 6/6 commit: look up commit info in metapackJeff King, Jan 29, 2013
  38. Duy NguyenJan 30, 2013
  39. Jeff KingJan 30, 2013
  40. Duy NguyenJan 30, 2013
  41. Shawn PearceJan 31, 2013
  42. Jeff KingFeb 1, 2013
  43. Shawn PearceFeb 2, 2013

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