On Wed, Apr 12, 2023 at 4:23 PM Greg Stark <st...@mit.edu> wrote: > I'm trying to wrap my head around GetOldestNonRemovableTransactionId() > and whether it's the right thing here. This comment is not helping me: > > /* > * Return the oldest XID for which deleted tuples must be preserved in the > * passed table. > * > * If rel is not NULL the horizon may be considerably more recent than > * otherwise (i.e. fewer tuples will be removable). In the NULL case a horizon > * that is correct (but not optimal) for all relations will be returned. > * > * This is used by VACUUM to decide which deleted tuples must be preserved in > * the passed in table. > */ > > > Am I crazy or is the parenthetical comment there exactly backwards? If > the horizon is *more recent* then fewer tuples are *non*-removable. > I.e. *more* tuples are removable, no?
Isn't it the non-parenthetical part that's wrong? I would expect that if we don't know which relation it is, the horizon might be considerably LESS recent, which would result in fewer tuples being removable. -- Robert Haas EDB: http://www.enterprisedb.com
