This requires some core changes as well so that we can properly
WAL-log the truncation. Specifically, it changes the format of the
XLOG_SMGR_TRUNCATE WAL record, so bump XLOG_PAGE_MAGIC.
Patch by me, reviewed but not fully endorsed by Andres Freund.
The new pg_check_visible() and pg_check_frozen() functions can be used to
verify that the visibility map bits for a relation's data pages match the
actual state of the tuples on those pages.
Amit Kapila and Robert Haas, reviewed (in earlier versions) by Andres
Freund. Additional testing help by Thomas Munro.
This lets you examine the visibility map as well as page-level
visibility information. I initially wrote it as a debugging aid,
but was encouraged to polish it for commit.
Patch by me, reviewed by Masahiko Sawada.
Discussion: 56D77803.6080503@BlueTreble.com
