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Re: [PATCH/RFC v3 01/13] Move index v2 specific functions to their own file

From
Thomas Rast <trast@student.ethz.ch>
Date
Aug 10, 2012, 14:24 UTC
Message-ID
<87hasan7ty.fsf@thomas.inf.ethz.ch>
In-Reply-To
<7vtxwbn2qe.fsf@alter.siamese.dyndns.org>
Junio C Hamano <gitster@pobox.com> writes:
Show 9 quoted lines
> If you found that an entry you read halfway has an inconsistent crc,
> and if you suspect that is because somebody else was writing to the
> same index, it is a _sure_ sign that you are not alone, and all the
> entries you read so far to the core, even if they weren't touched by
> that sombody else when you read them, may be stale, and worse yet,
> what you are going to read may be inconsistent with what you've read
> and have in-core (e.g. you may have read "f" before somebody else
> that is racing with you have turned it into a directory, and your
> next read may find "f/d" in the index without crc error).

The intention for v5 (admittedly this probably requires a lot more documentation) was to only allow an in-place update in two cases:

* updating the data fields (*not* the name) of a file entry,
* adding or removing conflict entries at the end.

The latter probably requires a bit more thought to make it safe, too. But I think the idea always was that any write that changes the basic layout of the file (so that you would read something wrong) will need a full rewrite. Otherwise we're too far in DB land. Most updates will be of the "update the stat and/or sha1 of a file" kind, anyway.

-- 
Thomas Rast
trast@{inf,student}.ethz.ch
Previous: Nguyen Thai Ngoc DuyNext: Junio C Hamano
Message 9 of 34 in “Introduce index file format version 5”
  1. 0/13 Introduce index file format version 5Thomas Gummerer, Aug 8, 2012
  2. 01/13 Move index v2 specific functions to their own fileThomas Gummerer, Aug 8, 2012
  3. Nguyen Thai Ngoc DuyAug 8, 2012
  4. Thomas GummererAug 8, 2012
  5. Junio C HamanoAug 9, 2012
  6. Thomas GummererAug 9, 2012
  7. Junio C HamanoAug 10, 2012
  8. Nguyen Thai Ngoc DuyAug 10, 2012
  9. Thomas RastAug 10, 2012
  10. Junio C HamanoAug 10, 2012
  11. Thomas GummererAug 10, 2012
  12. 02/13 t2104: Don't fail for index versions other than [23]Thomas Gummerer, Aug 8, 2012
  13. 03/13 t3700: Avoid interfering with the racy codeThomas Gummerer, Aug 8, 2012
  14. 04/13 Add documentation of the index-v5 file formatThomas Gummerer, Aug 8, 2012
  15. Junio C HamanoAug 9, 2012
  16. Thomas GummererAug 9, 2012
  17. Junio C HamanoAug 9, 2012
  18. 05/13 Make in-memory format aware of stat_crcThomas Gummerer, Aug 8, 2012
  19. 06/13 Read index-v5Thomas Gummerer, Aug 8, 2012
  20. Nguyen Thai Ngoc DuyAug 8, 2012
  21. Johannes SixtAug 8, 2012
  22. Junio C HamanoAug 8, 2012
  23. Thomas GummererAug 8, 2012
  24. 07/13 Read resolve-undo dataThomas Gummerer, Aug 8, 2012
  25. Junio C HamanoAug 9, 2012
  26. Thomas GummererAug 9, 2012
  27. Junio C HamanoAug 10, 2012
  28. Thomas GummererAug 10, 2012
  29. 08/13 Read cache-tree in index-v5Thomas Gummerer, Aug 8, 2012
  30. 09/13 Write index-v5Thomas Gummerer, Aug 8, 2012
  31. 10/13 Write index-v5 cache-tree dataThomas Gummerer, Aug 8, 2012
  32. 11/13 Write resolve-undo data for index-v5Thomas Gummerer, Aug 8, 2012
  33. 12/13 update-index.c: always rewrite the index when index-version is givenThomas Gummerer, Aug 8, 2012
  34. 13/13 p0002-index.sh: add perf test for the index formatsThomas Gummerer, Aug 8, 2012

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