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Re: [PATCH 1/3] diff histogram: intern strings

From
Johannes Schindelin <johannes.schindelin@gmx.de>
Date
Nov 19, 2021, 15:49 UTC
Message-ID
<nycvar.QRO.7.76.6.2111191647100.63@tvgsbejvaqbjf.bet>
In-Reply-To
<86d38148-7b97-76aa-148b-346cc179615a@gmail.com>
Hi Phillip,
On Fri, 19 Nov 2021, Phillip Wood wrote:
Show 21 quoted lines
> On 18/11/2021 15:42, Jeff King wrote:
> > On Thu, Nov 18, 2021 at 04:35:48PM +0100, Johannes Schindelin wrote:
> >
> > > I think the really important thing to point out is that
> > > `xdl_classify_record()` ensures that the `ha` attribute is different
> > > for different text. AFAIR it even "linearizes" the `ha` values, i.e.
> > > they won't be all over the place but start at 0 (or 1).
> > >
> > > So no, I'm not worried about collisions. That would be a bug in
> > > `xdl_classify_record()` and I think we would have caught this bug by
> > > now.
> >
> > Ah, thanks for that explanation. That addresses my collision concern
> > from earlier in the thread completely.
>
> Yes, thanks for clarifying I should have been clearer in my reply to
> Stolee. The reason I was waffling on about file sizes is that there can
> only be a collision if there are more than 2^32 unique lines. I think
> the minimum file size where that happens is just below 10GB when one
> side of the diff has 2^31 lines and the other has 2^31 + 1 lines and all
> the lines are unique.

Indeed, and as you pointed out, we already refuse to generate diffs for such large amounts of data.

(For what it's worth, I totally agree with punting on such large data, it would also take too long a time to generate diffs on such large data to be reasonable.)

Ciao, Dscho

Previous: Jeff KingNext: Phillip Wood via GitGitGadget
Message 12 of 15 in “xdiff: speedup histogram diff”
  1. 0/3 xdiff: speedup histogram diffPhillip Wood via GitGitGadget, Nov 17, 2021
  2. 1/3 diff histogram: intern stringsPhillip Wood via GitGitGadget, Nov 17, 2021
  3. Derrick StoleeNov 17, 2021
  4. Jeff KingNov 17, 2021
  5. Phillip WoodNov 17, 2021
  6. Johannes SchindelinNov 18, 2021
  7. Jeff KingNov 18, 2021
  8. Phillip WoodNov 19, 2021
  9. Jeff KingNov 19, 2021
  10. Ævar Arnfjörð BjarmasonNov 19, 2021
  11. Jeff KingNov 19, 2021
  12. Johannes SchindelinNov 19, 2021
  13. 2/3 xdiff: avoid unnecessary memory allocationsPhillip Wood via GitGitGadget, Nov 17, 2021
  14. 3/3 xdiff: simplify comparisonPhillip Wood via GitGitGadget, Nov 17, 2021
  15. Johannes SchindelinNov 18, 2021

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