Yesterday I reported a WAL problem that could lead to tuples not being
marked as committed-good or committed-dead after we'd already removed
the pg_clog segment that had their transaction's commit status.
I wasn't completely satisfied with that, though, because on further
reflection it seemed a very low-probability mechanism. I kept digging,
and finally came to the kind of bug that qualifies as a big DOH :-(
If you run a database-wide VACUUM (one with no specific target table
mentioned) as a non-superuser, then the VACUUM doesn't process tables
that don't belong to you. But it will advance pg_database.datvacuumxid
anyway, which means that pg_clog could be truncated while old transaction
references still remain unmarked in those other tables.
In words of one syllable: running VACUUM as a non-superuser can cause
irrecoverable data loss in any 7.2.* release.
I think this qualifies as a "must fix" bug. I recommend we back-patch
a fix for this into the REL7_2 branch and put out a 7.2.3 release.
We should also fix the "can't wait without a PROC" bug that was solved
a few days ago.
regards, tom lane
