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Re: [PATCH v2 01/10] Define a structure for object IDs.

From
Junio C Hamano <gitster@pobox.com>
Date
Mar 14, 2015, 22:19 UTC
Message-ID
<xmqqbnjvw7c8.fsf@gitster.dls.corp.google.com>
In-Reply-To
<CACsJy8BeFO3RQJ6pU5+q6E4n3A36X9PgYoi7xB_NQ4C_JYaP5w@mail.gmail.com>
Duy Nguyen <pclouds@gmail.com> writes:
Show 12 quoted lines
>> Anyway, wouldn't this be all academic?  I do not see how you would
>> keep the object name in the <pack, nth> format in-core, as the
>> obj_hash[] is a hashtable keyed by <sha-1>, and even when we switch
>> to a different hash, I cannot see how such a table to ensure the
>> singleton-ness of in-core objects can be keyed sometimes by <hash>
>> and by <pack, nth> in some other time.
>
> I'm implementing something to see how much we gain by avoiding object
> lookup. The current approach is having "struct object ** obj" in
> "struct packed_git", indexed by "nth". So when you have <pack, nth>
> and pack->obj[nth] is valid, you'll get to "struct object *" without
> hashing.

But do you realize that the hashtable serves two purposes? Grab the object from its name is one thing, and the other one I am not seeing how you will make it work with "sometimes <sha-1> sometimes <pack,nth>" is to ensure that we will have only one in-core copy for the same object. We even walk the hashtable when we want to drop the flag bits from all in-core objects, so even if you instanciated an in-core object without going through the object name layer, the hashtable needs to have a pointer to such a pointer, no?

Previous: Duy NguyenNext: Duy Nguyen
Message 34 of 36 in “Use a structure for object IDs.”
  1. 00/10 Use a structure for object IDs.brian m. carlson, Mar 7, 2015
  2. 01/10 Define a structure for object IDs.brian m. carlson, Mar 7, 2015
  3. 02/10 Define utility functions for object IDs.brian m. carlson, Mar 7, 2015
  4. Duy NguyenMar 8, 2015
  5. brian m. carlsonMar 8, 2015
  6. Michael HaggertyMar 11, 2015
  7. 03/10 bisect.c: convert leaf functions to use struct object_idbrian m. carlson, Mar 7, 2015
  8. 04/10 archive.c: convert to use struct object_idbrian m. carlson, Mar 7, 2015
  9. Michael HaggertyMar 11, 2015
  10. brian m. carlsonMar 11, 2015
  11. 05/10 zip: use GIT_SHA1_HEXSZ for trailersbrian m. carlson, Mar 7, 2015
  12. 06/10 bulk-checkin.c: convert to use struct object_idbrian m. carlson, Mar 7, 2015
  13. 07/10 diff: convert struct combine_diff_path to object_idbrian m. carlson, Mar 7, 2015
  14. 08/10 commit: convert parts to struct object_idbrian m. carlson, Mar 7, 2015
  15. Michael HaggertyMar 11, 2015
  16. 09/10 patch-id: convert to use struct object_idbrian m. carlson, Mar 7, 2015
  17. 10/10 apply: convert threeway_stage to object_idbrian m. carlson, Mar 7, 2015
  18. Junio C HamanoMar 8, 2015
  19. Kyle J. McKayMar 11, 2015
  20. Michael HaggertyMar 11, 2015
  21. Junio C HamanoMar 11, 2015
  22. brian m. carlsonMar 13, 2015
  23. brian m. carlsonMar 11, 2015
  24. Junio C HamanoMar 12, 2015
  25. brian m. carlsonMar 12, 2015
  26. Michael HaggertyMar 12, 2015
  27. brian m. carlsonMar 12, 2015
  28. Duy NguyenMar 12, 2015
  29. Junio C HamanoMar 12, 2015
  30. Junio C HamanoMar 12, 2015
  31. Duy NguyenMar 13, 2015
  32. Junio C HamanoMar 13, 2015
  33. Duy NguyenMar 14, 2015
  34. Junio C HamanoMar 14, 2015
  35. Duy NguyenMar 15, 2015
  36. Junio C HamanoMar 15, 2015

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