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# Copyright (c) 2024-2025, PostgreSQL Global Development Group
# Very simple exercise of direct I/O GUC.
use strict;
use warnings FATAL => 'all';
use Fcntl;
use IO::File;
use PostgreSQL::Test::Cluster;
use PostgreSQL::Test::Utils;
use Test::More;
# We know that macOS has F_NOCACHE, and we know that Windows has
# FILE_FLAG_NO_BUFFERING, and we assume that their typical file systems will
# accept those flags. For every other system, we'll probe for O_DIRECT
# support.
if ($^O ne 'darwin' && $^O ne 'MSWin32')
{
# Perl's Fcntl module knows if this system has O_DIRECT in <fcntl.h>.
if (defined &O_DIRECT)
{
# Can we open a file in O_DIRECT mode in the file system where
# tmp_check lives?
my $f = IO::File->new(
"${PostgreSQL::Test::Utils::tmp_check}/test_o_direct_file",
O_RDWR | O_DIRECT | O_CREAT);
if (!$f)
{
plan skip_all =>
"pre-flight test if we can open a file with O_DIRECT failed: $!";
}
$f->close;
}
else
{
plan skip_all => "no O_DIRECT";
}
}
my $node = PostgreSQL::Test::Cluster->new('main');
$node->init;
$node->append_conf(
'postgresql.conf', qq{
debug_io_direct = 'data,wal,wal_init'
shared_buffers = '256kB' # tiny to force I/O
wal_level = replica # minimal runs out of shared_buffers when set so tiny
});
$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();
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