Commits on Jun 25, 2024

1. Fix MVCC bug with prepared xact with subxacts on standby …

   We did not recover the subtransaction IDs of prepared transactions
   when starting a hot standby from a shutdown checkpoint. As a result,
   such subtransactions were considered as aborted, rather than
   in-progress. That would lead to hint bits being set incorrectly, and
   the subtransactions suddenly becoming visible to old snapshots when
   the prepared transaction was committed.
   
   To fix, update pg_subtrans with prepared transactions's subxids when
   starting hot standby from a shutdown checkpoint. The snapshots taken
   from that state need to be marked as "suboverflowed", so that we also
   check the pg_subtrans.
   
   Discussion: https://www.postgresql.org/message-id/6b852e98-2d49-4ca1-9e95-db419a2696e0%40iki.fi
   
   NEON: cherry-picked from the upstream thread ahead of time, to unblock
   #7288. I expect this to be
   committed to upstream in the next few days, superseding this. NOTE: I
   did not include the new regression test on v15 and v14 branches,
   because the test would need some adapting, and we don't run the perl
   tests on Neon anyway.

   

   hlinnaka committed Jun 25, 2024
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