All such code deals with this global variable in one of three ways.
Sometimes the same functions use it in more than one of these ways
at the same time.
First, sometimes it's an implicit argument to one or more functions
being called in xlog.c or elsewhere, and must be set to the
appropriate value before calling those functions lest they
misbehave. In those cases, it is now passed as an explicit argument
instead.
Second, sometimes it's used to obtain the current timeline after
the end of recovery, i.e. the timeline to which WAL is being
written and flushed. Such code now calls GetWALInsertionTimeLine()
or relies on the new out parameter added to GetFlushRecPtr().
Third, sometimes it's used during recovery to store the current
replay timeline. That can change, so such code must generally
update the value before each use. It can still do that, but must
now use a local variable instead.
The net effect of these changes is to reduce by a fair amount the
amount of code that is directly accessing this global variable.
That's good, because history has shown that we don't always think
clearly about which timeline ID it's supposed to contain at any
given point in time, or indeed, whether it has been or needs to
be initialized at any given point in the code.
Patch by me, reviewed and tested by Michael Paquier, Amul Sul, and
Álvaro Herrera.
Discussion: https://postgr.es/m/CA+TgmobfAAqhfWa1kaFBBFvX+5CjM=7TE=n4r4Q1o2bjbGYBpA@mail.gmail.com
WAL records may span multiple segments, but XLogWrite() does not
wait for the entire record to be written out to disk before
creating archive status files. Instead, as soon as the last WAL page of
the segment is written, the archive status file is created, and the
archiver may process it. If PostgreSQL crashes before it is able to
write and flush the rest of the record (in the next WAL segment), the
wrong version of the first segment file lingers in the archive, which
causes operations such as point-in-time restores to fail.
To fix this, keep track of records that span across segments and ensure
that segments are only marked ready-for-archival once such records have
been completely written to disk.
This has always been wrong, so backpatch all the way back.
Author: Nathan Bossart <bossartn@amazon.com>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Ryo Matsumura <matsumura.ryo@fujitsu.com>
Reviewed-by: Andrey Borodin <x4mmm@yandex-team.ru>
Discussion: https://postgr.es/m/CBDDFA01-6E40-46BB-9F98-9340F4379505@amazon.com
The definitions of the routines defined in xlogarchive.c have been part
of xlog_internal.h which is included by several frontend tools, but all
those routines are only called by the backend. More cleanup could be
done within xlog_internal.h, but that's already a nice cut.
This will help a follow-up patch for pg_rewind where handling of
restore_command is added for frontends.
Author: Alexey Kondratov, Michael Paquier
Reviewed-by: Álvaro Herrera, Alexander Korotkov
Discussion: https://postgr.es/m/a3acff50-5a0d-9a2c-b3b2-ee36168955c1@postgrespro.ru
Bruce Momjian
Fujii Masao
Robert Haas
Alvaro Herrera
Michael Paquier