Re: [Patch] ALTER SYSTEM READ ONLY

On Wed, Sep 22, 2021 at 6:59 PM Mark Dilger
<mark.dilger@enterprisedb.com> wrote:
>
>
>
> > On Sep 22, 2021, at 6:14 AM, Amul Sul <sulamul@gmail.com> wrote:
> >
> >> Attached patch v34-0010 adds a test of cursors opened FOR UPDATE interacting with a system that is set read-only by a different session.  The expected output is worth reviewing to see how this plays out.  I don't see anything in there which is obviously wrong, but some of it is a bit clunky.  For example, by the time the client sees an error "FATAL:  WAL is now prohibited", the system may already have switched back to read-write.  Also, it is a bit strange to get one of these errors on an attempted ROLLBACK.  Once again, not wrong as such, but clunky.
> >>
> >
> > Can't we do the same in the TAP test? If the intention is only to test
> > session termination when the system changes to WAL are prohibited then
> > that I have added in the latest version, but that test does not
> > reinitiate the same connection again, I think that is not possible
> > there too.
>
> Perhaps you can point me to a TAP test that does this in a concise fashion.  When I tried writing a TAP test for this, it was much longer than the equivalent isolation test spec.
>

Yes, that is a bit longer, here is the snip from v35-0010 patch:

+my $psql_timeout = IPC::Run::timer(60);
+my ($mysession_stdin, $mysession_stdout, $mysession_stderr) = ('', '', '');
+my $mysession = IPC::Run::start(
+ [
+ 'psql', '-X', '-qAt', '-v', 'ON_ERROR_STOP=1', '-f', '-', '-d',
+ $node_primary->connstr('postgres')
+ ],
+ '<',
+ \$mysession_stdin,
+ '>',
+ \$mysession_stdout,
+ '2>',
+ \$mysession_stderr,
+ $psql_timeout);
+
+# Write in transaction and get backend pid
+$mysession_stdin .= q[
+BEGIN;
+INSERT INTO tab VALUES(7);
+SELECT $$value-7-inserted-into-tab$$;
+];
+$mysession->pump until $mysession_stdout =~ /value-7-inserted-into-tab[\r\n]$/;
+like($mysession_stdout, qr/value-7-inserted-into-tab/,
+ 'started write transaction in a session');
+$mysession_stdout = '';
+$mysession_stderr = '';
+
+# Change to WAL prohibited
+$node_primary->safe_psql('postgres', 'SELECT pg_prohibit_wal(true)');
+is($node_primary->safe_psql('postgres', $show_wal_prohibited_query), 'on',
+ 'server is changed to wal prohibited by another session');
+
+# Try to commit open write transaction.
+$mysession_stdin .= q[
+COMMIT;
+];
+$mysession->pump;
+like($mysession_stderr, qr/FATAL:  WAL is now prohibited/,
+ 'session with open write transaction is terminated');

Regards,
Amul