pgsql: Eliminate COPY FREEZE use of XLOG_HEAP2_VISIBLE

Eliminate COPY FREEZE use of XLOG_HEAP2_VISIBLE

Instead of emitting a separate WAL XLOG_HEAP2_VISIBLE record for setting
bits in the VM, specify the VM block changes in the
XLOG_HEAP2_MULTI_INSERT record.

This halves the number of WAL records emitted by COPY FREEZE.

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

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d96f87332b3786abd23cba47459546799c562b8c

Modified Files
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src/backend/access/heap/heapam.c | 43 ++++++++++++--------
src/backend/access/heap/heapam_xlog.c | 49 ++++++++++++++++++++++-
src/backend/access/heap/visibilitymap.c | 70 ++++++++++++++++++++++++++++++++-
src/backend/access/rmgrdesc/heapdesc.c | 6 +++
src/include/access/visibilitymap.h | 4 ++
5 files changed, 154 insertions(+), 18 deletions(-)