Robert Haas <robertmhaas@gmail.com> writes:
> ... It's not
> like a 16-bit checksum was state-of-the-art even when we introduced
> it. We just did it because we had 2 bytes that we could repurpose
> relatively painlessly, and not any larger number. And that's still the
> case today, so at least in the short term we will have to choose some
> other solution to this problem.
Indeed. I propose the attached, which also fixes the unsafe use
of seek() alongside syswrite(), directly contrary to what "man perlfunc"
says to do.
regards, tom lane
diff --git a/src/bin/pg_checksums/t/002_actions.pl b/src/bin/pg_checksums/t/002_actions.pl
index 62c608eaf6..8c70453a45 100644
--- a/src/bin/pg_checksums/t/002_actions.pl
+++ b/src/bin/pg_checksums/t/002_actions.pl
@@ -24,6 +24,7 @@ sub check_relation_corruption
my $tablespace = shift;
my $pgdata = $node->data_dir;
+ # Create table and discover its filesystem location.
$node->safe_psql(
'postgres',
"CREATE TABLE $table AS SELECT a FROM generate_series(1,10000) AS a;
@@ -37,9 +38,6 @@ sub check_relation_corruption
my $relfilenode_corrupted = $node->safe_psql('postgres',
"SELECT relfilenode FROM pg_class WHERE relname = '$table';");
- # Set page header and block size
- my $pageheader_size = 24;
- my $block_size = $node->safe_psql('postgres', 'SHOW block_size;');
$node->stop;
# Checksums are correct for single relfilenode as the table is not
@@ -55,8 +53,12 @@ sub check_relation_corruption
# Time to create some corruption
open my $file, '+<', "$pgdata/$file_corrupted";
- seek($file, $pageheader_size, SEEK_SET);
- syswrite($file, "\0\0\0\0\0\0\0\0\0");
+ my $pageheader;
+ sysread($file, $pageheader, 24) or die "sysread failed";
+ # This inverts the pd_checksum field (only); see struct PageHeaderData
+ $pageheader ^= "\0\0\0\0\0\0\0\0\xff\xff";
+ sysseek($file, 0, 0) or die "sysseek failed";
+ syswrite($file, $pageheader) or die "syswrite failed";
close $file;
# Checksum checks on single relfilenode fail
