002_pg_upgrade.pl: Move pg_dump test code for better stability

The alleged "statistics pg_dump bug" that prevented us from enabling
stats dumping in commit 172259afb5 wasn't a pg_dump bug after all: it
was just a side effect of not running pg_dump at the right time (namely,
before giving autovacuum some time to do its thing and then disabling it
to stabilize things).  Move the code around to fix this problem and
enable statistics dumping.

Author: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Diagnosed-by: Jeff Davis <pgsql@j-davis.com>
Discussion: https://postgr.es/m/5f3703fd7f27da62a8f3615218f937507f522347.camel@j-davis.com
Discussion: https://postgr.es/m/CAExHW5sDm+aGb7A4EXK=X9rkrmSPDgc03EdADt=wWkdMO=XPSA@mail.gmail.com

src/bin/pg_upgrade/t/002_pg_upgrade.pl

@@ -83,10 +83,9 @@ sub get_dump_for_comparison
 	open(my $dh, '>', $dump_adjusted)
 	  || die "could not open $dump_adjusted for writing $!";
 
-	# Don't dump statistics, because there are still some bugs.
 	$node->run_log(
 		[
-			'pg_dump', '--no-sync', '--no-statistics',
+			'pg_dump', '--no-sync',
 			'-d' => $node->connstr($db),
 			'-f' => $dumpfile
 		]);
@@ -301,64 +300,9 @@ else
 	is($rc, 0, 'regression tests pass');
 }
 
-# Test that dump/restore of the regression database roundtrips cleanly.  This
-# doesn't work well when the nodes are different versions, so skip it in that
-# case.  Note that this isn't a pg_restore test, but it's convenient to do it
-# here because we've gone to the trouble of creating the regression database.
-#
-# Do this while the old cluster is running before it is shut down by the
-# upgrade test.
-SKIP:
-{
-	my $dstnode = PostgreSQL::Test::Cluster->new('dst_node');
-
-	skip "different Postgres versions"
-	  if ($oldnode->pg_version != $dstnode->pg_version);
-	skip "source node not using default install"
-	  if (defined $oldnode->install_path);
-
-	# Dump the original database for comparison later.
-	my $src_dump =
-	  get_dump_for_comparison($oldnode, 'regression', 'src_dump', 1);
-
-	# Setup destination database cluster
-	$dstnode->init(%old_node_params);
-	# Stabilize stats for comparison.
-	$dstnode->append_conf('postgresql.conf', 'autovacuum = off');
-	$dstnode->start;
-
-	my $dump_file = "$tempdir/regression.dump";
-
-	# Use --create in dump and restore commands so that the restored
-	# database has the same configurable variable settings as the original
-	# database so that the dumps taken from both databases taken do not
-	# differ because of locale changes. Additionally this provides test
-	# coverage for --create option.
-	#
-	# Use directory format so that we can use parallel dump/restore.
-	$oldnode->command_ok(
-		[
-			'pg_dump', '-Fd', '-j2', '--no-sync',
-			'-d' => $oldnode->connstr('regression'),
-			'--create', '-f' => $dump_file
-		],
-		'pg_dump on source instance');
-
-	$dstnode->command_ok(
-		[ 'pg_restore', '--create', '-j2', '-d' => 'postgres', $dump_file ],
-		'pg_restore to destination instance');
-
-	my $dst_dump =
-	  get_dump_for_comparison($dstnode, 'regression', 'dest_dump', 0);
-
-	compare_files($src_dump, $dst_dump,
-		'dump outputs from original and restored regression databases match');
-}
-
 # Initialize a new node for the upgrade.
 my $newnode = PostgreSQL::Test::Cluster->new('new_node');
 
-
 # The new cluster will be initialized with different locale settings,
 # but these settings will be overwritten with those of the original
 # cluster.
@@ -409,10 +353,66 @@ if (defined($ENV{oldinstall}))
 	}
 }
 
-# Stabilize stats before pg_dumpall.
+# Stabilize stats before pg_dump / pg_dumpall. Doing it after initializing
+# the new node gives enough time for autovacuum to update statistics on the
+# old node.
 $oldnode->append_conf('postgresql.conf', 'autovacuum = off');
 $oldnode->restart;
 
+# Test that dump/restore of the regression database roundtrips cleanly.  This
+# doesn't work well when the nodes are different versions, so skip it in that
+# case.  Note that this isn't a pg_upgrade test, but it's convenient to do it
+# here because we've gone to the trouble of creating the regression database.
+#
+# Do this while the old cluster is running before it is shut down by the
+# upgrade test but after turning its autovacuum off for stable statistics.
+SKIP:
+{
+	my $dstnode = PostgreSQL::Test::Cluster->new('dst_node');
+
+	skip "different Postgres versions"
+	  if ($oldnode->pg_version != $dstnode->pg_version);
+	skip "source node not using default install"
+	  if (defined $oldnode->install_path);
+
+	# Setup destination database cluster with the same configuration as the
+	# source cluster to avoid any differences between dumps taken from both the
+	# clusters caused by differences in their configurations.
+	$dstnode->init(%old_node_params);
+	# Stabilize stats for comparison.
+	$dstnode->append_conf('postgresql.conf', 'autovacuum = off');
+	$dstnode->start;
+
+	# Use --create in dump and restore commands so that the restored
+	# database has the same configurable variable settings as the original
+	# database so that the dumps taken from both databases taken do not
+	# differ because of locale changes. Additionally this provides test
+	# coverage for --create option.
+	#
+	# Use directory format so that we can use parallel dump/restore.
+	my $dump_file = "$tempdir/regression.dump";
+	$oldnode->command_ok(
+		[
+			'pg_dump', '-Fd', '-j2', '--no-sync',
+			'-d' => $oldnode->connstr('regression'),
+			'--create', '-f' => $dump_file
+		],
+		'pg_dump on source instance');
+
+	$dstnode->command_ok(
+		[ 'pg_restore', '--create', '-j2', '-d' => 'postgres', $dump_file ],
+		'pg_restore to destination instance');
+
+	# Dump original and restored database for comparison.
+	my $src_dump =
+	  get_dump_for_comparison($oldnode, 'regression', 'src_dump', 1);
+	my $dst_dump =
+	  get_dump_for_comparison($dstnode, 'regression', 'dest_dump', 0);
+
+	compare_files($src_dump, $dst_dump,
+		'dump outputs from original and restored regression databases match');
+}
+
 # Take a dump before performing the upgrade as a base comparison. Note
 # that we need to use pg_dumpall from the new node here.
 my @dump_command = (