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Re: [PATCH v2 1/8] packfile: prepare for the existence of '*.rev' files

From
Jeff King <peff@peff.net>
Date
Jan 25, 2021, 18:27 UTC
Message-ID
<YA8NdHJloTf15qXf@coredump.intra.peff.net>
In-Reply-To
<YA8DlQwSzNZXq+AU@nand.local>
On Mon, Jan 25, 2021 at 12:44:53PM -0500, Taylor Blau wrote:
Show 12 quoted lines
> Thanks for including a compelling argument in favor of the approach that
> I took in this patch.
> 
> I added something along the lines of what you suggested to the final
> paragraph, so now it concludes nicely instead of ending in a comma. I
> briefly considered whether I should add something about how these
> operations scale and how the warming efforts are really amortized across
> all of the objects, but I decided against it.
> 
> I think that this argument is already documented here, and that there's
> no way to concisely state it in an already long patch. Interested
> readers will easily be able to find our discussion here, which is good.
That sounds good. It is sort of arguing against a strawman anyway.
Show 5 quoted lines
> > It mostly looks good to me. I agree with Junio that "compute" is a
> > better verb than "load" for generating the in-memory revindex.
> 
> Yeah, I settled on load_pack_revindex() either calling
> "create_pack_revindex_in_memory()" or "load_pack_revindex_from_disk()".
Perfect.
Show 24 quoted lines
> > If p->revindex_data were "const uint32_t *", then this line would just
> > be:
> >
> >   return get_be32(p->revindex_data + pos);
> >
> > Not a huge deal either way since the whole point is to abstract this
> > behind a function where it only has to be written once. I don't think
> > there is any downside from the compiler's view (and we already use this
> > trick for the bitmap name-hash cache).
> 
> Honestly, I'm not a huge fan of implicitly scaling pos by
> sizeof(*p->revindex_data), but I can understand why it reads more
> clearly here. I don't really feel strongly either way, so I'm happy to
> change it in favor of your suggestion.
> 
> Of course, since RIDX_HEADER_SIZE is in bytes, not uint32_t's (and it
> has to be, since it's also used in the RIDX_MIN_SIZE macro, which is
> compared against the st_size of stating the .rev file), you have to do
> gross stuff like:
> 
>   p->revindex_data = (const uint32_t *)((const char *)p->revindex_map + RIDX_HEADER_SIZE);
> 
> But I guess the tradeoff is worth it, since the readers are easier to
> parse.

Yeah, that is definitely a downside. Perhaps keeping everything in bytes makes things a bit more obvious. In which case I might suggest that revindex_data just be a "const char *". You'd have to scale any pointer computations at the point of use then, but you'd avoid needing to do any extra casting.

-Peff
Previous: Taylor BlauNext: Junio C Hamano
Message 30 of 82 in “pack-revindex: introduce on-disk '.rev' format”
  1. 0/8 pack-revindex: introduce on-disk '.rev' formatTaylor Blau, Jan 8, 2021
  2. 2/8 pack-write.c: prepare to write 'pack-*.rev' filesTaylor Blau, Jan 8, 2021
  3. 8/8 pack-revindex: ensure that on-disk reverse indexes are given precedenceTaylor Blau, Jan 8, 2021
  4. 3/8 builtin/index-pack.c: write reverse indexesTaylor Blau, Jan 8, 2021
  5. 1/8 packfile: prepare for the existence of '*.rev' filesTaylor Blau, Jan 8, 2021
  6. 4/8 builtin/pack-objects.c: respect 'pack.writeReverseIndex'Taylor Blau, Jan 8, 2021
  7. 7/8 t: support GIT_TEST_WRITE_REV_INDEXTaylor Blau, Jan 8, 2021
  8. Derrick StoleeJan 12, 2021
  9. Taylor BlauJan 12, 2021
  10. Ævar Arnfjörð BjarmasonJan 12, 2021
  11. Derrick StoleeJan 12, 2021
  12. Taylor BlauJan 12, 2021
  13. 6/8 t: prepare for GIT_TEST_WRITE_REV_INDEXTaylor Blau, Jan 8, 2021
  14. Ævar Arnfjörð BjarmasonJan 12, 2021
  15. Taylor BlauJan 12, 2021
  16. 5/8 Documentation/config/pack.txt: advertise 'pack.writeReverseIndex'Taylor Blau, Jan 8, 2021
  17. 0/8 pack-revindex: introduce on-disk '.rev' formatTaylor Blau, Jan 13, 2021
  18. 8/8 pack-revindex: ensure that on-disk reverse indexes are given precedenceTaylor Blau, Jan 13, 2021
  19. 6/8 t: prepare for GIT_TEST_WRITE_REV_INDEXTaylor Blau, Jan 13, 2021
  20. 1/8 packfile: prepare for the existence of '*.rev' filesTaylor Blau, Jan 13, 2021
  21. Junio C HamanoJan 14, 2021
  22. Derrick StoleeJan 14, 2021
  23. Jeff KingJan 14, 2021
  24. Taylor BlauJan 14, 2021
  25. Junio C HamanoJan 14, 2021
  26. Taylor BlauJan 14, 2021
  27. Junio C HamanoJan 14, 2021
  28. Jeff KingJan 22, 2021
  29. Taylor BlauJan 25, 2021
  30. Jeff KingJan 25, 2021
  31. Junio C HamanoJan 25, 2021
  32. Taylor BlauJan 25, 2021
  33. 5/8 Documentation/config/pack.txt: advertise 'pack.writeReverseIndex'Taylor Blau, Jan 13, 2021
  34. 4/8 builtin/pack-objects.c: respect 'pack.writeReverseIndex'Taylor Blau, Jan 13, 2021
  35. Jeff KingJan 22, 2021
  36. Jeff KingJan 23, 2021
  37. Taylor BlauJan 25, 2021
  38. Jeff KingJan 25, 2021
  39. 2/8 pack-write.c: prepare to write 'pack-*.rev' filesTaylor Blau, Jan 13, 2021
  40. Jeff KingJan 22, 2021
  41. Taylor BlauJan 25, 2021
  42. Jeff KingJan 26, 2021
  43. 7/8 t: support GIT_TEST_WRITE_REV_INDEXTaylor Blau, Jan 13, 2021
  44. 3/8 builtin/index-pack.c: write reverse indexesTaylor Blau, Jan 13, 2021
  45. Jeff KingJan 22, 2021
  46. Taylor BlauJan 25, 2021
  47. 00/10 pack-revindex: introduce on-disk '.rev' formatTaylor Blau, Jan 25, 2021
  48. 01/10 packfile: prepare for the existence of '*.rev' filesTaylor Blau, Jan 25, 2021
  49. Jeff KingJan 29, 2021
  50. Taylor BlauJan 29, 2021
  51. Jeff KingJan 30, 2021
  52. 08/10 t: support GIT_TEST_WRITE_REV_INDEXTaylor Blau, Jan 25, 2021
  53. Jeff KingJan 29, 2021
  54. 07/10 t: prepare for GIT_TEST_WRITE_REV_INDEXTaylor Blau, Jan 25, 2021
  55. Jeff KingJan 29, 2021
  56. Eric SunshineJan 29, 2021
  57. Taylor BlauJan 29, 2021
  58. Jeff KingJan 30, 2021
  59. Junio C HamanoJan 29, 2021
  60. 05/10 builtin/pack-objects.c: respect 'pack.writeReverseIndex'Taylor Blau, Jan 25, 2021
  61. 09/10 pack-revindex: ensure that on-disk reverse indexes are given precedenceTaylor Blau, Jan 25, 2021
  62. Jeff KingJan 29, 2021
  63. Taylor BlauJan 29, 2021
  64. Jeff KingJan 30, 2021
  65. 10/10 t5325: check both on-disk and in-memory reverse indexTaylor Blau, Jan 25, 2021
  66. Jeff KingJan 29, 2021
  67. Jeff KingJan 29, 2021
  68. Taylor BlauJan 29, 2021
  69. Jeff KingJan 30, 2021
  70. 06/10 Documentation/config/pack.txt: advertise 'pack.writeReverseIndex'Taylor Blau, Jan 25, 2021
  71. Jeff KingJan 29, 2021
  72. Taylor BlauJan 29, 2021
  73. Jeff KingJan 30, 2021
  74. 02/10 pack-write.c: prepare to write 'pack-*.rev' filesTaylor Blau, Jan 25, 2021
  75. 04/10 builtin/index-pack.c: write reverse indexesTaylor Blau, Jan 25, 2021
  76. 03/10 builtin/index-pack.c: allow stripping arbitrary extensionsTaylor Blau, Jan 25, 2021
  77. Jeff KingJan 29, 2021
  78. Taylor BlauJan 29, 2021
  79. Junio C HamanoJan 26, 2021
  80. Taylor BlauJan 26, 2021
  81. Jeff KingJan 29, 2021
  82. Taylor BlauJan 29, 2021

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