pgsql: Correct heap vacuum boundary state setup ordering

Correct heap vacuum boundary state setup ordering

052026c9b9 mistakenly reordered setup steps in heap_vacuum_rel(),
incorrectly moving RelationGetNumberOfBlocks() before
vacuum_get_cutoffs().

OldestXmin must be determined before RelationGetNumberOfBlocks()
calculates the number of blocks in the relation that will be vacuumed.
Otherwise tuples older than OldestXmin may be inserted into the end of
the relation into blocks that are not vacuumed. If additional tuples
newer than those inserted into unscanned blocks but older than
OldestXmin are inserted into free space earlier in the relation, the
result could be advancing pg_class.relfrozenxid to a newer value than an
unfrozen XID in one of the unscanned heap pages.

Assigning an incorrect relfrozenxid can lead to data loss, so it is
imperative that it correctly reflect the oldest unfrozen xid.

Reported-by: Peter Geoghegan <pg(at)bowt(dot)ie>
Author: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Reviewed-by: Peter Geoghegan <pg(at)bowt(dot)ie>
Discussion: https://postgr.es/m/CAH2-WzntqvVEdbbpqG5JqSZGuLWmy4PBfUO-OswfivKchr2gvw%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/31a7e175fd8f6079555f2bba95c7cc118236bb20

Modified Files
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src/backend/access/heap/vacuumlazy.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)