pgsql: WAL log VM setting during vacuum phase I in XLOG_HEAP2_PRUNE_VAC

WAL log VM setting during vacuum phase I in XLOG_HEAP2_PRUNE_VACUUM_SCAN

Vacuum no longer emits a separate WAL record for each page set
all-visible or all-frozen during phase I. Instead, visibility map
updates are now included in the XLOG_HEAP2_PRUNE_VACUUM_SCAN record that
is already emitted for pruning and freezing.

Previously, heap_page_prune_and_freeze() determined whether a page was
all-visible, but the corresponding VM bits were only set later in
lazy_scan_prune(). Now the VM is updated immediately in
heap_page_prune_and_freeze(), at the same time as the heap
modifications. This reduces WAL volume produced by vacuum.

For now, vacuum is still the only user of heap_page_prune_and_freeze()
allowed to set the VM. On-access pruning is not yet able to set the VM.

Author: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Reviewed-by: Andres Freund <andres(at)anarazel(dot)de>
Reviewed-by: Kirill Reshke <reshkekirill(at)gmail(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Earlier version Reviewed-by: Robert Haas <robertmhaas(at)gmail(dot)com>
Discussion: https://postgr.es/m/flat/CAAKRu_ZMw6Npd_qm2KM%2BFwQ3cMOMx1Dh3VMhp8-V7SOLxdK9-g%40mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/1252a4ee28636734d68f1acd33be45399c83dc53

Modified Files
--------------
src/backend/access/heap/pruneheap.c | 245 +++++++++++++++++++++++++----------
src/backend/access/heap/vacuumlazy.c | 113 ++--------------
src/include/access/heapam.h | 37 +++---
3 files changed, 205 insertions(+), 190 deletions(-)