A few weeks back I sent a bug report [1] directly to the -bugs mailing list, and I haven't seen any activity on it (maybe this is because I emailed directly instead of using the form?), but I got some time to take a look and concluded that a first-level fix is pretty simple.
A quick background refresher: after promoting a standby rewinding the
former primary requires that a checkpoint have been completed on the
new primary after promotion. This is correctly documented. However
pg_rewind incorrectly reports to the user that a rewind isn't
necessary because the source and target are on the same timeline.
Specifically, this happens when the control file on the newly promoted
server looks like:
Latest checkpoint's TimeLineID: 4
Latest checkpoint's PrevTimeLineID: 4
...
Min recovery ending loc's timeline: 5
Attached is a patch that detects this condition and reports it as an
error to the user.
In the spirit of the new-ish "ensure shutdown" functionality I could
imagine extending this to automatically issue a checkpoint when this
situation is detected. I haven't started to code that up, however,
wanting to first get buy-in on that.
Thanks,
James Coleman
1:
https://www.postgresql.org/message-id/CAAaqYe8b2DBbooTprY4v=bized9qbqvlq+fd9j617eqfjk1...@mail.gmail.com
v1-0001-pg_rewind-warn-if-we-haven-t-checkpointed-after-p.patch
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