2 files changed, 58 insertions, 0 deletions
diff --git a/src/test/modules/test_misc/meson.build b/src/test/modules/test_misc/meson.build
index 21bde427b41..911084ac0fe 100644
--- a/src/test/modules/test_misc/meson.build
+++ b/src/test/modules/test_misc/meson.build
@@ -9,6 +9,7 @@ tests += {
       't/001_constraint_validation.pl',
       't/002_tablespace.pl',
       't/003_check_guc.pl',
+      't/004_io_direct.pl',
     ],
   },
 }
diff --git a/src/test/modules/test_misc/t/004_io_direct.pl b/src/test/modules/test_misc/t/004_io_direct.pl
new file mode 100644
index 00000000000..f5bf0b11e4e
--- /dev/null
+++ b/src/test/modules/test_misc/t/004_io_direct.pl
@@ -0,0 +1,57 @@
+# Very simple exercise of direct I/O GUC.
+
+use strict;
+use warnings;
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Systems that we know to have direct I/O support, and whose typical local
+# filesystems support it or at least won't fail with an error.  (illumos should
+# probably be in this list, but perl reports it as solaris.  Solaris should not
+# be in the list because we don't support its way of turning on direct I/O, and
+# even if we did, its version of ZFS rejects it, and OpenBSD just doesn't have
+# it.)
+if (!grep { $^O eq $_ } qw(aix darwin dragonfly freebsd linux MSWin32 netbsd))
+{
+	plan skip_all => "no direct I/O support";
+}
+
+my $node = PostgreSQL::Test::Cluster->new('main');
+$node->init;
+$node->append_conf(
+	'postgresql.conf', qq{
+io_direct = 'data,wal,wal_init'
+shared_buffers = '256kB' # tiny to force I/O
+});
+$node->start;
+
+# Do some work that is bound to generate shared and local writes and reads as a
+# simple exercise.
+$node->safe_psql('postgres',
+	'create table t1 as select 1 as i from generate_series(1, 10000)');
+$node->safe_psql('postgres', 'create table t2count (i int)');
+$node->safe_psql(
+	'postgres', qq{
+begin;
+create temporary table t2 as select 1 as i from generate_series(1, 10000);
+update t2 set i = i;
+insert into t2count select count(*) from t2;
+commit;
+});
+$node->safe_psql('postgres', 'update t1 set i = i');
+is( '10000',
+	$node->safe_psql('postgres', 'select count(*) from t1'),
+	"read back from shared");
+is( '10000',
+	$node->safe_psql('postgres', 'select * from t2count'),
+	"read back from local");
+$node->stop('immediate');
+
+$node->start;
+is( '10000',
+	$node->safe_psql('postgres', 'select count(*) from t1'),
+	"read back from shared after crash recovery");
+$node->stop;
+
+done_testing();