Avoid unfortunate IPC::Run path caching in PostgresNode

Commit b34ca595 provided for installation-aware instances of
PostgresNode. However, it turns out that IPC::Run works against this by
caching the path to a binary and not consulting the path again, even if
it has changed. We work around this by calling Postgres binaries with
the installed path rather than just a bare name to be looked up in the
environment path, if there is an installed path. For the common case
where there is no installed path we continue to use the bare command
name.

Diagnosis and solution from Mark Dilger

Discussion: https://postgr.es/m/E8F512F8-B4D6-4514-BA8D-2E671439DA92@enterprisedb.com

src/test/perl/PostgresNode.pm

@@ -1271,6 +1271,28 @@ sub _get_env
 	return (%inst_env);
 }
 
+# Private routine to get an installation path qualified command.
+#
+# IPC::Run maintains a cache, %cmd_cache, mapping commands to paths.  Tests
+# which use nodes spanning more than one postgres installation path need to
+# avoid confusing which installation's binaries get run.  Setting $ENV{PATH} is
+# insufficient, as IPC::Run does not check to see if the path has changed since
+# caching a command.
+sub installed_command
+{
+    my ($self, $cmd) = @_;
+
+    # Nodes using alternate installation locations use their installation's
+    # bin/ directory explicitly
+    return join('/', $self->{_install_path}, 'bin', $cmd)
+        if defined $self->{_install_path};
+
+    # Nodes implicitly using the default installation location rely on IPC::Run
+    # to find the right binary, which should not cause %cmd_cache confusion,
+    # because no nodes with other installation paths do it that way.
+    return $cmd;
+}
+
 =pod
 
 =item get_free_port()
@@ -1568,7 +1590,8 @@ sub psql
 	}
 	$psql_connstr .= defined $replication ? " replication=$replication" : "";
 
-	my @psql_params = ('psql', '-XAtq', '-d', $psql_connstr, '-f', '-');
+	my @psql_params = ($self->installed_command('psql'),
+					   '-XAtq', '-d', $psql_connstr, '-f', '-');
 
 	# If the caller wants an array and hasn't passed stdout/stderr
 	# references, allocate temporary ones to capture them so we
@@ -1754,7 +1777,7 @@ sub background_psql
 	my $replication = $params{replication};
 
 	my @psql_params = (
-		'psql',
+		$self->installed_command('psql'),
 		'-XAtq',
 		'-d',
 		$self->connstr($dbname)
@@ -1831,7 +1854,8 @@ sub interactive_psql
 
 	local %ENV = $self->_get_env();
 
-	my @psql_params = ('psql', '-XAt', '-d', $self->connstr($dbname));
+	my @psql_params = ($self->installed_command('psql'),
+					   '-XAt', '-d', $self->connstr($dbname));
 
 	push @psql_params, @{ $params{extra_params} }
 	  if defined $params{extra_params};
@@ -2041,7 +2065,8 @@ sub poll_query_until
 
 	$expected = 't' unless defined($expected);    # default value
 
-	my $cmd = [ 'psql', '-XAt', '-c', $query, '-d', $self->connstr($dbname) ];
+	my $cmd = [ $self->installed_command('psql'),
+				'-XAt', '-c', $query, '-d', $self->connstr($dbname) ];
 	my ($stdout, $stderr);
 	my $max_attempts = 180 * 10;
 	my $attempts     = 0;
@@ -2461,7 +2486,8 @@ sub pg_recvlogical_upto
 	croak 'endpos must be specified'    unless defined($endpos);
 
 	my @cmd = (
-		'pg_recvlogical', '-S', $slot_name, '--dbname',
+		$self->installed_command('pg_recvlogical'),
+		'-S', $slot_name, '--dbname',
 		$self->connstr($dbname));
 	push @cmd, '--endpos', $endpos;
 	push @cmd, '-f', '-', '--no-loop', '--start';