Re: [HACKERS] [COMMITTERS] pgsql: Fix freezing of a dead HOT-updated tuple

I think you've done a stellar job of identifying what the actual problem
was. I like the new (simpler) coding of that portion of
HeapTupleSatisfiesVacuum.

freeze-the-dead is not listed in isolation_schedule; an easy fix.
I confirm that the test crashes with an assertion failure without the
code fix, and that it doesn't with it.

I think the comparison to OldestXmin should be reversed:

if (!TransactionIdPrecedes(xmax, OldestXmin))
return HEAPTUPLE_RECENTLY_DEAD;

return HEAPTUPLE_DEAD;

This way, an xmax that has exactly the OldestXmin value will return
RECENTLY_DEAD rather DEAD, which seems reasonable to me (since
OldestXmin value itself is supposed to be still possibly visible to
somebody). Also, this way it is consistent with the other comparison to
OldestXmin at the bottom of the function. There is no reason for the
"else" or the extra braces.

Put together, I propose the attached delta for 0001.

Your commit message does a poor job of acknowledging prior work on
diagnosing the problem starting from Dan's initial test case and patch.

I haven't looked at your 0002 yet.

--
Álvaro Herrera https://www.2ndQuadrant.com/
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