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

Hi,

On 2017-12-06 13:21:15 -0300, Alvaro Herrera wrote:
> 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.

Thanks!

> freeze-the-dead is not listed in isolation_schedule; an easy fix.

Yea, I'd sent an update about that, stupidly forgot git amend the
commit...

> 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).

Yes, I think you're right. That's a bug.

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

Yea, you're right. I was writing it with 14h of jetlag, apparently that
does something to your brain...

Greetings,

Andres Freund