How pg_dump interact with not MVCC-safe commands?
As I understand, pg_dump first take snapshot and then lock all tables
it intended to dump. What happens if not MVCC-safe command committed
after snapshot but before lock? From comment to pg_dump.c I understand
that it may fail with 'cache lookup failed' error. But, can it happen,
that pg_dump not fail, but instead capture inconsistent dump? For
example TRUNCATE committed after snapshot and pg_dump will see result
of TRUNCATE but not result of other commands in TRUNCATE transaction?
