| From: | Andrey Borodin <x4mmm(at)yandex-team(dot)ru> |
|---|---|
| To: | Vaijayanti Bharadwaj <vaijayanti(dot)bharadwaj(at)enterprisedb(dot)com> |
| Cc: | pgsql-hackers mailing list <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: SSI: A patch for a Serializability violation |
| Date: | 2026-08-31 08:07:18 |
| Message-ID: | 84AA5B50-06F5-4FD6-84CC-88477710AA5C@yandex-team.ru |
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| Lists: | pgsql-hackers |
Hi Vaijayanti,
Jacob reported what looks like the same bug earlier [0], and I sent a
tentative commitSeqNo-based fix in that thread.
Your patch made me notice a case which we did not consider there: imported
serializable snapshots. lastCommitBeforeSnapshot is recorded when the
snapshot is imported, while finishedBefore is compared with the imported
snapshot's xmin. The two approaches can therefore disagree about a reader
which commits between export and import. Your patch preserves the existing
non-summarized behavior in this case; mine does not.
Was this case part of your reasoning? It seems worth writing explicitly the
expected behavior here.
Thank you!
Best regards, Andrey Borodin.
[0] https://postgr.es/m/CA%2BCOZaCtK%3DUQbeQwdAoRw27J%2B58bJBC%2ByNHP4OH2%2By_t2UtFAg%40mail.gmail.com
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