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

On Thu, Dec 14, 2017 at 6:30 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> Pushed this way. Moved some more relfrozenxid/relminmxid tests outside
> of the cutoff changes, polished some error messages.
>
>
> Alvaro, Michael, Peter, and everyone else I'd greatly appreciate if you
> could have a look at the backported version, just about everything but
> v10 had conflicts, some of them not insubstantial.

I have one minor piece of feedback on the upgrading of assertions to
ereport()s with ERRCODE_DATA_CORRUPTION: It would be nice if you could
upgrade the raw elog() "can't happen" error within
IndexBuildHeapRangeScan() to be an ereport() with
ERRCODE_DATA_CORRUPTION. I'm referring to the "failed to find parent
tuple for heap-only tuple" error, which I think merits being a real
user-visible error, just like the relfrozenxid/relminmxid tests are
now. As you know, the enhanced amcheck will sometimes detect
corruption due to this bug by hitting that error.

It would be nice if we could tighten up the number of errcodes that
can be involved in an error that amcheck detects. I know that elog()
implicitly has an errcode, that could be included in the errcodes to
check when verification occurs in an automated fashion across a large
number of databases. However, this is a pretty esoteric point, and I'd
prefer to just try to limit it to ERRCODE_DATA_CORRUPTION and
ERRCODE_INDEX_CORRUPTED, insofar as that's practical. When we ran
amcheck on the Heroku fleet, back when I worked there, there were all
kinds of non-interesting errors that could occur that needed to be
filtered out. I want to try to make that process somewhat less painful.

--
Peter Geoghegan