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Re: two questions about the format of loose object

From
LYLiu Yubao <yubao.liu@gmail.com>
Date
Dec 1, 2008, 09:28 UTC
Message-ID
<4933AE55.2090007@gmail.com>
In-Reply-To
<7voczws3np.fsf@gitster.siamese.dyndns.org>
Junio C Hamano wrote:
Show 19 quoted lines
> Liu Yubao <yubao.liu@gmail.com> writes:
> 
> 
> A hint for understanding why loose objects are compressed is that
> packfiles were invented much later in the history of git.
> 
> These are both good questions, and it might have made a difference if they
> were posed in early April 2005.
> 
> At this point, the plain and clear answer to both of these "Why not"
> questions is "because that is the way it is and it is costly to change
> them now in thousands of repositories people use every day."
> 
> In other words, it is not interesting anymore to raise these questions
> now, especially as a suggestion to change the system, unless they are
> accompanied by arguments that convinces everybody that the cost of such a
> change outweighs the benefits, and a clear transition plans how to upgrade
> everybody's existing repositories without any pain.
>

Thanks for your explanation, but I doubt if it's too costly to change the format of loose object, after all this doesn't change the format of pack file and affect git-pull/fetch of old git client.

I ask the "why not" questions because I doubt if I miss some technical points that the change isn't worth at all in fact.

If no severe technical problem will occur, I think it's worth breaking *forward* compatibility for better performance and I'm willing to implement it.

Some cons and pros.
cons:
* old git client can't read loose objects in new format
  (People degrade git rarely and old git can read pack files
   generated by new git, so it's not a big problem)
pros:
* avoid compressing and uncompressing loose objects that are likely
  frequently used when you are coding/merging
* share loose objects among multipe git processes
* the new code path is simpler although we will have more code paths for
  compatibility
Best regards,
Liu Yubao
Previous: Junio C HamanoNext: Jakub Narebski
Message 3 of 27 in “two questions about the format of loose object”
  1. Liu YubaoDec 1, 2008
  2. Junio C HamanoDec 1, 2008
  3. Liu YubaoDec 1, 2008
  4. Jakub NarebskiDec 1, 2008
  5. Liu YubaoDec 2, 2008
  6. Shawn O. PearceDec 1, 2008
  7. Liu YubaoDec 2, 2008
  8. 0/5 support reading and writing uncompressed loose objectLiu Yubao, Dec 2, 2008
  9. 1/5 avoid parse_sha1_header() accessing memory out of boundLiu Yubao, Dec 2, 2008
  10. Shawn O. PearceDec 2, 2008
  11. Liu YubaoDec 3, 2008
  12. 2/5 don't die immediately when convert an invalid type nameLiu Yubao, Dec 2, 2008
  13. 3/5 optimize parse_sha1_header() a little by detecting object typeLiu Yubao, Dec 2, 2008
  14. Shawn O. PearceDec 2, 2008
  15. Liu YubaoDec 3, 2008
  16. 4/5 support reading uncompressed loose objectLiu Yubao, Dec 2, 2008
  17. Shawn O. PearceDec 2, 2008
  18. Liu YubaoDec 3, 2008
  19. 5/5 support writing uncompressed loose objectLiu Yubao, Dec 2, 2008
  20. Shawn O. PearceDec 2, 2008
  21. Liu YubaoDec 3, 2008
  22. Liu YubaoDec 2, 2008
  23. Nick AndrewDec 1, 2008
  24. Liu YubaoDec 2, 2008
  25. Shawn O. PearceDec 1, 2008
  26. Liu YubaoDec 2, 2008
  27. Nicolas PitreDec 4, 2008

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