Cherry-pick: Fix MVCC bug with prepared xact with subxacts on standby (v14) #449
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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 neondatabase/neon#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.
knizhnik
approved these changes
Jun 25, 2024
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See neondatabase/neon#8152 for the main PR in the neon repo