Archive timeline history files in standby if archive_mode is set to "always".

Previously the standby server didn't archive timeline history files
streamed from the primary even when archive_mode is set to "always",
while it archives the streamed WAL files. This could cause the PITR to
fail because there was no required timeline history file in the archive.
The cause of this issue was that walreceiver didn't mark those files as
ready for archiving.

This commit makes walreceiver mark those streamed timeline history
files as ready for archiving if archive_mode=always. Then the archiver
process archives the marked timeline history files.

Back-patch to all supported versions.

Reported-by: Grigory Smolkin
Author: Grigory Smolkin, Fujii Masao
Reviewed-by: David Zhang, Anastasia Lubennikova
Discussion: https://postgr.es/m/54b059d4-2b48-13a4-6f43-95a087c92367@postgrespro.ru

doc/src/sgml/high-availability.sgml

@@ -1395,7 +1395,8 @@ synchronous_standby_names = 'ANY 2 (s1, s2, s3)'
      If <varname>archive_mode</varname> is set to <literal>on</literal>, the
      archiver is not enabled during recovery or standby mode. If the standby
      server is promoted, it will start archiving after the promotion, but
-     will not archive any WAL it did not generate itself. To get a complete
+     will not archive any WAL or timeline history files that
+     it did not generate itself. To get a complete
      series of WAL files in the archive, you must ensure that all WAL is
      archived, before it reaches the standby. This is inherently true with
      file-based log shipping, as the standby can only restore files that

src/backend/replication/walreceiver.c

@@ -758,6 +758,15 @@ WalRcvFetchTimeLineHistoryFiles(TimeLineID first, TimeLineID last)
 			 */
 			writeTimeLineHistoryFile(tli, content, len);
 
+			/*
+			 * Mark the streamed history file as ready for archiving
+			 * if archive_mode is always.
+			 */
+			if (XLogArchiveMode != ARCHIVE_MODE_ALWAYS)
+				XLogArchiveForceDone(fname);
+			else
+				XLogArchiveNotify(fname);
+
 			pfree(fname);
 			pfree(content);
 		}