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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