Re: Timeline switching with partial WAL records can break replica recovery

> let the new timeline start after incomplete contrecord
This approach seems like it could prevent issues with archiving. Upon
reconsideration, I agree that we shouldn’t alter the complete timeline —
instead, the missing contrecord should be detected in the next timeline.
However, there’s a problem with the ordering of the `EndOfRecovery` and
`MissingContrecord` records: `EndOfRecovery` must be written to WAL at the
very beginning of the new timeline. This conflicts with the current design,
so we should rethink the solution.
The first easy solution that comes to my mind is to simply extend the
`EndOfRecovery` record by adding an `overwritten_lsn` field. As I see it,
it won’t change the code much. What do you think?

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Alena Vinter