Date: Wed, 14 Apr 2021 17:13:30 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Postgres hackers <pgsql-hackers@lists.postgresql.org>
Subject: File truncation within PostgresNode::issues_sql_like() wrong on
 Windows
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Hi all,

As fairywren has proved a couple of days ago, it is not really a good
idea to rely on a file truncation to check for patterns in the logs of
the backend:
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=fairywren&dt=2021-04-07%2013%3A29%3A28

Visibly, a logic based on the log file truncation fails on Windows
because of the concurrent access of the backend that outputs its logs
there.  In PostgresNode.pm, connect_ok() and connect_access() enforce
a rotation of the log file before restarting the server on Windows to
make sure that a given step does not find logs generated by a previous
test, but that's not the case of issues_sql_like().  Looking at the
existing tests using this routine (src/bin/scripts/), I have found on
test in 090_reindexdb.pl that could lead to a false positive.  The
test is marked in the patch attached, just for awareness.

Would there be any objections to change this routine so as we avoid
the file truncation on Windows?  The patch attached achieves that.

Any thoughts?
--
Michael

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diff --git a/src/bin/scripts/t/090_reindexdb.pl b/src/bin/scripts/t/090_rei=
ndexdb.pl
index 159b637230..8b06218d6b 100644
--- a/src/bin/scripts/t/090_reindexdb.pl
+++ b/src/bin/scripts/t/090_reindexdb.pl
@@ -174,6 +174,7 @@ $node->command_fails(
 $node->command_fails(
 	[ 'reindexdb', '-j', '2', '-i', 'i1', 'postgres' ],
 	'parallel reindexdb cannot process indexes');
+# XXX The first query maps with a test above.
 $node->issues_sql_like(
 	[ 'reindexdb', '-j', '2', 'postgres' ],
 	qr/statement:\ REINDEX SYSTEM postgres;
diff --git a/src/test/perl/PostgresNode.pm b/src/test/perl/PostgresNode.pm
index e26b2b3f30..9daa438ccc 100644
--- a/src/test/perl/PostgresNode.pm
+++ b/src/test/perl/PostgresNode.pm
@@ -2195,7 +2195,8 @@ Run a command on the node, then verify that $expected=
_sql appears in the
 server log file.
=20
 Reads the whole log file so be careful when working with large log outputs.
-The log file is truncated prior to running the command, however.
+The log file is truncated prior to running the command, and on Windows, a
+rotation of the log file is done before restarting the node.
=20
 =3Dcut
=20
@@ -2207,7 +2208,18 @@ sub issues_sql_like
=20
 	local %ENV =3D $self->_get_env();
=20
-	truncate $self->logfile, 0;
+	# On Windows, the truncation would not work, so rotate the log
+	# file before restarting the server afresh.
+	if ($TestLib::windows_os)
+	{
+		$self->rotate_logfile;
+		$self->restart;
+	}
+	else
+	{
+		truncate $self->logfile, 0;
+	}
+
 	my $result =3D TestLib::run_log($cmd);
 	ok($result, "@$cmd exit code 0");
 	my $log =3D TestLib::slurp_file($self->logfile);

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