On Fri, Jul 5, 2019 at 3:14 PM Peter Geoghegan <pg@bowt.ie> wrote:
> On Fri, Jul 5, 2019 at 8:49 AM Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> > > TRAP: FailedAssertion(»!(metad->btm_version >= 3)«, Datei:
> > > »/build/postgresql-12-3URvLF/postgresql-12-12~beta2/build/../src/backend/access/nbtree/nbtpage.c«,
> > > Zeile: 665)
> >
> > Seems that _bt_getrootheight is too optimistic about the metapage
> > version it'll find. I suppose this could be handled by just not caching
> > the metapage if it is of the old version ... or maybe by calling
> > _bt_upgrademetapage().
>
> The problem here predates v12 -- the call to _bt_cachemetadata() was
> added to _bt_getrootheight() by commit 0a64b45152b, which went into
> v11. My commit dd299df8189 added a new assertion that fails, but
> that's just a symptom -- I changed the code in _bt_getrootheight() to
> use a BTMetaPageData pointer to shared memory (i.e. a pointer to the
> authoritative version), rather than using the newly-out-of-sync cached
> version. It shouldn't be out-of-sync at all.
>
> _bt_getrootheight() is mostly just something that exists for the
> planner, so it has no business calling _bt_cachemetadata(), which will
> "upgrade" the cached metadata image from version 2 to version 3 if it
> happens to be on version 2. How can it be okay to upgrade the cached
> version without also upgrading the on-disk/shared_buffers version?
> This bug was hiding in plain sight.
CC'ing Alexander, who was also involved in commit 0a64b45152b...
--
Peter Geoghegan