On Tue, Mar 27, 2018 at 02:02:10PM -0400, Tom Lane wrote: > Robert Haas <robertmh...@gmail.com> writes: >> On Tue, Mar 27, 2018 at 11:41 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: >>> This is ignoring the possibility of damaged data in between, ie >>> A ... B ... CHKPT ... C ... a few zeroed pages ... D ... CHKPT ... E ... F > >> It's hard for me to believe that this case matters very much. If >> you're trying to run pg_rewind on a system where the WAL segments >> contain a few zeroed pages, you're probably going to be hosed anyway, >> if not by this particular thing then by something else. > > Well, the point of checkpoints is that WAL data before the last one > should no longer matter anymore, isn't it?
I have to agree with Tom here. If you force pg_rewind to replay more WAL records from a checkpoint older than the checkpoint prior to where WAL has forked at promotion then you have a risk of losing data. Remember, this comes close to the recent thread where we discussed that keeping in pg_wal WAL segments worth more than the last completed checkpoints could lead to corruption if you try to replay from that, which led to 4b0d28d. -- Michael
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