pg_upgrade: start/stop new server after pg_resetwal

When commit 0f33a719 removed the
instructions to start/stop the new cluster before running rsync, it was
now possible for pg_resetwal/pg_resetxlog to leave the final WAL record
at wal_level=minimum, preventing upgraded standby servers from
reconnecting.

This patch fixes that by having pg_upgrade unconditionally start/stop
the new cluster after pg_resetwal/pg_resetxlog has run.

Backpatch through 9.2 since, though the instructions were added in PG
9.5, they worked all the way back to 9.2.

Discussion: https://postgr.es/m/20170620171844.GC24975@momjian.us

Backpatch-through: 9.2

src/bin/pg_upgrade/check.c

@@ -174,23 +174,25 @@ report_clusters_compatible(void)
 
 
 void
-issue_warnings(void)
+issue_warnings_and_set_wal_level(void)
 {
+	/*
+	 * We unconditionally start/stop the new server because pg_resetwal -o
+	 * set wal_level to 'minimum'.  If the user is upgrading standby
+	 * servers using the rsync instructions, they will need pg_upgrade
+	 * to write its final WAL record showing wal_level as 'replica'.
+	 */
+	start_postmaster(&new_cluster, true);
+
 	/* Create dummy large object permissions for old < PG 9.0? */
 	if (GET_MAJOR_VERSION(old_cluster.major_version) <= 804)
-	{
-		start_postmaster(&new_cluster, true);
 		new_9_0_populate_pg_largeobject_metadata(&new_cluster, false);
-		stop_postmaster(false);
-	}
 
 	/* Reindex hash indexes for old < 10.0 */
 	if (GET_MAJOR_VERSION(old_cluster.major_version) <= 906)
-	{
-		start_postmaster(&new_cluster, true);
 		old_9_6_invalidate_hash_indexes(&new_cluster, false);
+
 	stop_postmaster(false);
-	}
 }
 
 

src/bin/pg_upgrade/pg_upgrade.c

@@ -162,7 +162,7 @@ main(int argc, char **argv)
 	create_script_for_cluster_analyze(&analyze_script_file_name);
 	create_script_for_old_cluster_deletion(&deletion_script_file_name);
 
-	issue_warnings();
+	issue_warnings_and_set_wal_level();
 
 	pg_log(PG_REPORT, "\nUpgrade Complete\n");
 	pg_log(PG_REPORT, "----------------\n");

src/bin/pg_upgrade/pg_upgrade.h

@@ -332,7 +332,7 @@ void		output_check_banner(bool live_check);
 void		check_and_dump_old_cluster(bool live_check);
 void		check_new_cluster(void);
 void		report_clusters_compatible(void);
-void		issue_warnings(void);
+void		issue_warnings_and_set_wal_level(void);
 void output_completion_banner(char *analyze_script_file_name,
 						 char *deletion_script_file_name);
 void		check_cluster_versions(void);