Put back stats-collector restarting code, removed accidentally.

Removed that code snippet accidentally in the archive_mode='always' patch.

Also, use varname-tags for archive_command in the docs.

Fujii Masao

doc/src/sgml/high-availability.sgml

@@ -1237,9 +1237,10 @@ primary_slot_name = 'node_a_slot'
      to <literal>always</literal>, and the standby will call the archive
      command for every WAL segment it receives, whether it's by restoring
      from the archive or by streaming replication. The shared archive can
-     be handled similarly, but the archive_command must test if the file
-     being archived exists already, and if the existing file has identical
-     contents. This requires more care in the archive_command, as it must
+     be handled similarly, but the <varname>archive_command</varname> must
+     test if the file being archived exists already, and if the existing file
+     has identical contents. This requires more care in the
+     <varname>archive_command</varname>, as it must
      be careful to not overwrite an existing file with different contents,
      but return success if the exactly same file is archived twice. And
      all that must be done free of race conditions, if two servers attempt

src/backend/postmaster/postmaster.c

@@ -1645,6 +1645,10 @@ ServerLoop(void)
 				start_autovac_launcher = false; /* signal processed */
 		}
 
+		/* If we have lost the stats collector, try to start a new one */
+		if (PgStatPID == 0 && pmState == PM_RUN)
+			PgStatPID = pgstat_start();
+
 		/*
 		 * If we have lost the archiver, try to start a new one.
 		 *