pgsql: Save prune cycles by consistently clearing prune hints on all-vi

Save prune cycles by consistently clearing prune hints on all-visible pages

All-visible pages can't contain prunable tuples. We already clear the
prune hint (pd_prune_xid) during pruning of all-visible pages, but we
were not doing so in vacuum phase three, nor initializing it for
all-frozen pages created by COPY FREEZE, and we were not clearing it on
standbys.

Because page hints are not WAL-logged, pages on a standby carry stale
pd_prune_xid values. After promotion, that stale hint triggers
unnecessary on-access pruning.

Fix this by clearing the prune hint everywhere we currently mark a heap
page all-visible. Clearing it when setting PD_ALL_VISIBLE ensures no
extra overhead.

Author: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Reviewed-by: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/flat/CAAKRu_b-BMOyu0X-0jc_8bWNSbQ5K6JTEueayEhcQuw-OkCSKg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8b9d42bf6bd29b855a6bee21aa6010c070980086

Modified Files
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src/backend/access/heap/heapam.c | 1 +
src/backend/access/heap/heapam_xlog.c | 7 +++++++
src/backend/access/heap/vacuumlazy.c | 3 +++
3 files changed, 11 insertions(+)