Gregory Stark <[EMAIL PROTECTED]> writes: > Breaking the chain up into pieces seems weird. It seems like it's obviously > bogus and only works because we're sure the tuples are dead anyways so it > doesn't really matter what we do with them.
Yup, exactly. If we wanted to be tense about this we'd try to get rid of the nominally RECENTLY_DEAD tuples that precede any DEAD tuple in the chain. However, I concur with Simon to the extent that I don't want to do any more work to fix this bug than necessary, and trying to recognize such tuples seems like a lot more work than necessary. Also, we know this case works because it already is working: in the situation where VACUUM happens to visit and remove the DEAD tuple(s) before reaching the RECENTLY_DEAD tuples that link forward to them, it treats the RECENTLY_DEAD tuples as a disconnected chain and moves them as-is. I saw tons of this in the traces I was making today, and it doesn't seem to create any bad effects. (My attention was drawn to it because I saw move_chain_tuple being used to move single-member chains, which looks impossible when you first look at the code --- the is-it-a-chain test seems to ensure that we can link either forward or backward. But not so if t_ctid points to an already-removed tuple.) regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend