While mucking around in src/backend/utils/time/tqual.c today, I noticed the following comment attached to HeapTupleSatisfiesNow:
* mao says 17 march 1993: the tests in this routine are correct; * if you think they're not, you're wrong, and you should think * about it again. i know, it happened to me. we don't need to * check commit time against the start time of this transaction * because 2ph locking protects us from doing the wrong thing. * if you mess around here, you'll break serializability. the only * problem with this code is that it does the wrong thing for system * catalog updates, because the catalogs aren't subject to 2ph, so * the serializability guarantees we provide don't extend to xacts * that do catalog accesses. this is unfortunate, but not critical. Much as I hate to disturb a comment just before its 19th birthday, the bit about two-phase locking and serializability hasn't been correct since around 1999 (when MVCC was added). :-) Dan -- Dan R. K. Ports MIT CSAIL http://drkp.net/ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
