Re: heap_tuple_needs_freeze false positive

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> I'm not convinced that it's a bug. Suppose that xmax is set but is
> hinted as invalid.

XMAX_INVALID is not a "hint". When it's set, the contents of the field
must be presumed to be garbage. Any code failing to adhere to that rule
is broken.

> We process the table and advanced relfrozenxid;
> then, we crash. After recovery, it's possible that the hint bit is
> gone (after all, setting hint bits isn't WAL-logged). Now we're in
> big trouble, because the next CLOG lookup on that xmax value might not
> happen until it's been reused, and we might get a different answer
> than before.

I believe we have adequate defenses against that, and even if we did
not, that doesn't make the code in question less wrong.

regards, tom lane