Bruce Momjian <[EMAIL PROTECTED]> writes: > I don't understand why a single counter is needed for phantom xids. We > keep the cmin/cmax on the tuple already, and our own backend can look up > the xmin/xmax that goes with the phantom.
Oh, so you're thinking of an internal table that provides a mapping back to the replaced xmin? Ugh. Perhaps it could be made to work, but it's a lot of mechanism, and it will slow down visibility checks (since AFAICS you'd have to check every subxid against the phantoms table). If we go with a global CID counter then we don't have to add that step. A global CID counter would also simplify other visibility tests. Alvaro hasn't said anything about how he's doing visibility checks across different subxacts of the same main xact, but without global CID there would need to be some pretty ugly checks to determine whether a subxact happened before or after the CID cutoff your outer xact is interested in. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]