On Sun, Jul 5, 2015 at 3:16 PM, Andres Freund <and...@anarazel.de> wrote: >>On the other hand, in the common case, by the time we perform a >>restartpoint, we're consistent: I think the main exception to that is >>if we do a base backup that spans multiple checkpoints. I think that >>in the new location, the chances that the legacy truncation is trying >>to read inconsistent data is probably higher. > > The primary problem isn't that we truncate too early, it's that we delay > truncation on the standby in comparison to the primary by a considerable > amount. All the while continuing to replay multi creations. > > I don't see the difference wrt. consistency right now, but I don't have > access to the code right now. I mean we *have* to do something while > inconsistent. A start/stop backup can easily span a day or four.
So, where are we with this patch? In my opinion, we ought to do something about master and 9.5 before beta, so that we're doing *yet another* major release with unfixed multixact bugs. Let's make the relevant truncation changes in master and 9.5 and bump the WAL page magic, so that a 9.5alpha standby can't be used with a 9.5beta master. Then, we don't need any of this legacy truncation stuff at all, and 9.5 is hopefully in a much better state than 9.4 and 9.3. Now, that still potentially leaves 9.4 and 9.3 users hanging out to dry. But we don't have a tremendous number of those people clamoring about this, and if we get 9.5+ correct, then we can go and change the logic in 9.4 and 9.3 later when, and if, we are confident that's the right thing to do. I am still not altogether convinced that it's a good idea, nor am I altogether convinced that this code is right. Perhaps it is, and if we consensus on it, fine. But regardless of that, we should not send a third major release to beta with the current broken system unless there is really no viable alternative. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
