Since pg_ctl promote already waits for recovery to end, these calls are
obsolete.

Per discussion, "location" is a rather vague term that could refer to
multiple concepts.  "LSN" is an unambiguous term for WAL locations and
should be preferred.  Some function names, view column names, and function
output argument names used "lsn" already, but others used "location",
as well as yet other terms such as "wal_position".  Since we've already
renamed a lot of things in this area from "xlog" to "wal" for v10,
we may as well incur a bit more compatibility pain and make these names
all consistent.

David Rowley, minor additional docs hacking by me

Discussion: https://postgr.es/m/CAKJS1f8O0njDKe8ePFQ-LK5-EjwThsDws6ohJ-+c6nWK+oUxtg@mail.gmail.com

Commit f82ec32a renamed the pg_xlog
directory to pg_wal.  To make things consistent, and because "xlog" is
terrible terminology for either "transaction log" or "write-ahead log"
rename all SQL-callable functions that contain "xlog" in the name to
instead contain "wal".  (Note that this may pose an upgrade hazard for
some users.)

Similarly, rename the xlog_position argument of the functions that
create slots to be called wal_position.

Discussion: https://www.postgresql.org/message-id/CA+Tgmob=YmA=H3DbW1YuOXnFVgBheRmyDkWcD9M8f=5bGWYEoQ@mail.gmail.com

This changes the default values of the following parameters:

wal_level = replica
max_wal_senders = 10
max_replication_slots = 10

in order to make it possible to make a backup and set up simple
replication on the default settings, without requiring a system restart.

Discussion: https://postgr.es/m/CABUevEy4PR_EAvZEzsbF5s+V0eEvw7shJ2t-AUwbHOjT+yRb3A@mail.gmail.com

Reviewed by Peter Eisentraut. Benchmark help from Tomas Vondra.

When a relation is truncated, it is important that the FSM is truncated as
well. Otherwise, after recovery, the FSM can return a page that has been
truncated away, leading to errors like:

ERROR:  could not read block 28991 in file "base/16390/572026": read only 0
of 8192 bytes

We were using MarkBufferDirtyHint() to dirty the buffer holding the last
remaining page of the FSM, but during recovery, that might in fact not
dirty the page, and the FSM update might be lost.

To fix, use the stronger MarkBufferDirty() function. MarkBufferDirty()
requires us to do WAL-logging ourselves, to protect from a torn page, if
checksumming is enabled.

Also fix an oversight in visibilitymap_truncate: it also needs to WAL-log
when checksumming is enabled.

Analysis by Pavan Deolasee.

Discussion: <CABOikdNr5vKucqyZH9s1Mh0XebLs_jRhKv6eJfNnD2wxTn=_9A@mail.gmail.com>