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A comment on Ask HN: We just had an actual UUID v4 collision.... Parent comment

Re:Ask HN: We just had an actual UUID v4 collision... by erikerikson on Friday May 08, 2026 @07:12PM (#48069911)
There are better approaches like pre -avoiding collisions but generating tends to be more expensive than checking.
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Re:Ask HN: We just had an actual UUID v4 collision... by orf on Friday May 08, 2026 @07:14PM (#48069932)
In what world is generating a UUID more expensive than checking for duplicates? at any scale?

Walk me through that please

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Re:Ask HN: We just had an actual UUID v4 collision... by erikerikson on Friday May 08, 2026 @07:18PM (#48069963)
Yeah, that was a little sloppy but it's generating is more expensive than not generating. In more words, generating an id and validating uniqueness is more expensive than only validating uniqueness.
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Re:Ask HN: We just had an actual UUID v4 collision... by soni96pl on Monday May 11, 2026 @05:39AM (#48092898)
UUID is used where checking is difficult, think distributed devices offline at a plantation. How could checking be easier in that case? It would require infrastructure that doesn't exist. There are many other cases where it's easier to handle collisions.
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Re:Ask HN: We just had an actual UUID v4 collision... by erikerikson on Monday May 11, 2026 @09:46AM (#48094950)
Agreed. While it's an uncommon scenario it is a significant case and UUID shouldn't be used in that case because as you write checking doesn't work well. Better to use an alternative such as coordinate/reserve monotonic producer IDs that get paired with monotonic, per-producer monotonic sequence IDs to produce guaranteed unique, well-ordered IDs.

[edit: in IOT it's common to issue x509 certificates as a type of authentication which could be used instead of using producer IDs. Solutions always have to be paired to use case.]

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Re:Ask HN: We just had an actual UUID v4 collision... by tommoneytools on Monday May 11, 2026 @05:42AM (#48092912) 

   Wild edge case. Curious if they ever found the root cause.
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Re:Ask HN: We just had an actual UUID v4 collision... by erikerikson on Monday May 11, 2026 @09:49AM (#48094987)
Welcome to Hacker News.

I suspect you meant to reply to a different comment. Regardless the most plausible speculation I've read here is that the RNG used to generate the UUID is low quality.

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