On 2018-Dec-21, Tom Lane wrote: > Alvaro Herrera <alvhe...@2ndquadrant.com> writes: > > Hmmm, I'm fairly sure you should have bumped XLOG_PAGE_MAGIC for this > > change. Otherwise, what is going to happen to an unpatched standby (of > > released versions) that receives the new WAL record from a patched > > primary? > > We can't change XLOG_PAGE_MAGIC in released branches, surely. > > I think the correct thing is just for the release notes to warn people > to upgrade standby servers first.
You're right. My memory is playing tricks on me. I recalled that we had done it to prevent replay of WAL replay in nonpatched standbys in some backpatched commit, but I can't find any evidence of this :-( The commit message for 8e9a16ab8f7f (in 9.3 branch after it was released) says: In replication scenarios using the 9.3 branch, standby servers must be upgraded before their master, so that they are prepared to deal with the new WAL record once the master is upgraded; failure to do so will cause WAL replay to die with a PANIC message. Later upgrade of the standby will allow the process to continue where it left off, so there's no disruption of the data in the standby in any case. Standbys know how to deal with the old WAL record, so it's okay to keep the master running the old code for a while. Stupidly, I checked the 9.4 version of that commit (then the master branch) and it does indeed contain the XLOG_PAGE_MAGIC change, but the 9.3 commit doesn't. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services