Fix brown paper bag bug in bbe08b8.

We must issue the TRUNCATE command first and update relfrozenxid
and relminmxid afterward; otherwise, TRUNCATE overwrites the
previously-set values.

Add a test case like I should have done the first time.

Per buildfarm report from TestUpgradeXversion.pm, by way of Tom
Lane.

src/bin/pg_dump/pg_dump.c

@@ -3141,7 +3141,7 @@ dumpDatabase(Archive *fout)
 		PGresult   *lo_res;
 		PQExpBuffer loFrozenQry = createPQExpBuffer();
 		PQExpBuffer loOutQry = createPQExpBuffer();
-		PQExpBuffer loVacQry = createPQExpBuffer();
+		PQExpBuffer loHorizonQry = createPQExpBuffer();
 		int			i_relfrozenxid,
 					i_relfilenode,
 					i_oid,
@@ -3168,14 +3168,14 @@ dumpDatabase(Archive *fout)
 		i_relfilenode = PQfnumber(lo_res, "relfilenode");
 		i_oid = PQfnumber(lo_res, "oid");
 
-		appendPQExpBufferStr(loOutQry, "\n-- For binary upgrade, set pg_largeobject relfrozenxid and relminmxid\n");
-		appendPQExpBufferStr(loVacQry, "\n-- For binary upgrade, preserve pg_largeobject and index relfilenodes\n");
+		appendPQExpBufferStr(loHorizonQry, "\n-- For binary upgrade, set pg_largeobject relfrozenxid and relminmxid\n");
+		appendPQExpBufferStr(loOutQry, "\n-- For binary upgrade, preserve pg_largeobject and index relfilenodes\n");
 		for (int i = 0; i < PQntuples(lo_res); ++i)
 		{
 			Oid		oid;
 			Oid		relfilenode;
 
-			appendPQExpBuffer(loOutQry, "UPDATE pg_catalog.pg_class\n"
+			appendPQExpBuffer(loHorizonQry, "UPDATE pg_catalog.pg_class\n"
 							  "SET relfrozenxid = '%u', relminmxid = '%u'\n"
 							  "WHERE oid = %u;\n",
 							  atooid(PQgetvalue(lo_res, i, i_relfrozenxid)),
@@ -3186,18 +3186,18 @@ dumpDatabase(Archive *fout)
 			relfilenode = atooid(PQgetvalue(lo_res, i, i_relfilenode));
 
 			if (oid == LargeObjectRelationId)
-				appendPQExpBuffer(loVacQry,
+				appendPQExpBuffer(loOutQry,
 								  "SELECT pg_catalog.binary_upgrade_set_next_heap_relfilenode('%u'::pg_catalog.oid);\n",
 								  relfilenode);
 			else if (oid == LargeObjectLOidPNIndexId)
-				appendPQExpBuffer(loVacQry,
+				appendPQExpBuffer(loOutQry,
 								  "SELECT pg_catalog.binary_upgrade_set_next_index_relfilenode('%u'::pg_catalog.oid);\n",
 								  relfilenode);
 		}
 
-		appendPQExpBufferStr(loVacQry,
+		appendPQExpBufferStr(loOutQry,
 							 "TRUNCATE pg_catalog.pg_largeobject;\n");
-		appendPQExpBufferStr(loOutQry, loVacQry->data);
+		appendPQExpBufferStr(loOutQry, loHorizonQry->data);
 
 		ArchiveEntry(fout, nilCatalogId, createDumpId(),
 					 ARCHIVE_OPTS(.tag = "pg_largeobject",
@@ -3208,8 +3208,8 @@ dumpDatabase(Archive *fout)
 		PQclear(lo_res);
 
 		destroyPQExpBuffer(loFrozenQry);
+		destroyPQExpBuffer(loHorizonQry);
 		destroyPQExpBuffer(loOutQry);
-		destroyPQExpBuffer(loVacQry);
 	}
 
 	PQclear(res);

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

@@ -161,6 +161,27 @@ sub generate_db
 	],
 	'dump before running pg_upgrade');
 
+# Also record the relfrozenxid and relminmxid horizons.
+my $horizon_query = <<EOM;
+SELECT
+  c.oid::regclass, c.relfrozenxid, c.relminmxid
+FROM
+  pg_class c, pg_namespace n
+WHERE
+  c.relnamespace = n.oid AND
+  ((n.nspname !~ '^pg_temp_' AND n.nspname !~ '^pg_toast_temp_' AND
+    n.nspname NOT IN ('pg_catalog', 'information_schema', 'binary_upgrade',
+                      'pg_toast'))
+  OR (n.nspname = 'pg_catalog' AND relname IN ('pg_largeobject')))
+EOM
+$horizon_query =~ s/\s+/ /g; # run it together on one line
+$newnode->command_ok(
+	[
+		'psql', '-At', '-d', $oldnode->connstr('postgres'),
+		'-o', "$tempdir/horizon1.txt", '-c', $horizon_query,
+	],
+	'horizons before running pg_upgrade');
+
 # After dumping, update references to the old source tree's regress.so
 # to point to the new tree.
 if (defined($ENV{oldinstall}))
@@ -294,6 +315,14 @@ sub generate_db
 	],
 	'dump after running pg_upgrade');
 
+# And second record of horizons as well.
+$newnode->command_ok(
+	[
+		'psql', '-At', '-d', $newnode->connstr('postgres'),
+		'-o', "$tempdir/horizon2.txt", '-c', $horizon_query,
+	],
+	'horizons after running pg_upgrade');
+
 # Compare the two dumps, there should be no differences.
 my $compare_res = compare("$tempdir/dump1.sql", "$tempdir/dump2.sql");
 is($compare_res, 0, 'old and new dumps match after pg_upgrade');
@@ -311,4 +340,21 @@ sub generate_db
 	print "=== EOF ===\n";
 }
 
+# Compare the horizons, there should be no differences.
+$compare_res = compare("$tempdir/horizon1.txt", "$tempdir/horizon2.txt");
+is($compare_res, 0, 'old and new horizons match after pg_upgrade');
+
+# Provide more context if the horizons do not match.
+if ($compare_res != 0)
+{
+	my ($stdout, $stderr) =
+	  run_command([ 'diff', "$tempdir/horizon1.txt", "$tempdir/horizon2.txt" ]);
+	print "=== diff of $tempdir/horizon1.txt and $tempdir/horizon2.txt\n";
+	print "=== stdout ===\n";
+	print $stdout;
+	print "=== stderr ===\n";
+	print $stderr;
+	print "=== EOF ===\n";
+}
+
 done_testing();