| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>, Mark Dilger <mark(dot)dilger(at)enterprisedb(dot)com>, Masahiko Sawada <masahiko(dot)sawada(at)2ndquadrant(dot)com>, "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru>, MBeena Emerson <mbeena(dot)emerson(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Andres Freund <andres(at)anarazel(dot)de>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net> |
| Subject: | Re: recovering from "found xmin ... from before relfrozenxid ..." |
| Date: | 2020-09-19 14:52:50 |
| Message-ID: | 686987.1600527170@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> writes:
> I think our assumption that changing the tests to have temp tables
> will make them safe w.r.t concurrent activity doesn't seem to be
> correct. We do set OldestXmin for temp tables aggressive enough that
> it allows us to remove all dead tuples but the test case behavior lies
> on whether we are able to prune the chain. AFAICS, we are using
> different cut-offs in heap_page_prune when it is called via
> lazy_scan_heap. So that seems to be causing both the failures.
Hm, reasonable theory.
I was able to partially reproduce whelk's failure here. I got a
couple of cases of "cannot freeze committed xmax", which then leads
to the second NOTICE diff; but I couldn't reproduce the first
NOTICE diff. That was out of about a thousand tries :-( so it's not
looking like a promising thing to reproduce without modifying the test.
I wonder whether "cannot freeze committed xmax" doesn't represent an
actual bug, ie is a7212be8b setting the cutoff *too* aggressively?
But if so, why's it so hard to reproduce?
regards, tom lane
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