diff --git a/src/bin/pg_rewind/RewindTest.pm b/src/bin/pg_rewind/RewindTest.pm
index 426bd6e5cf..e1c989afa6 100644
--- a/src/bin/pg_rewind/RewindTest.pm
+++ b/src/bin/pg_rewind/RewindTest.pm
@@ -66,8 +66,8 @@ our @EXPORT = qw(
   clean_rewind_test
 );
 
-our $test_master_datadir  = "$tmp_check/data_master";
-our $test_standby_datadir = "$tmp_check/data_standby";
+our $test_master_datadir  = "$tmp_check/data_master_$$";
+our $test_standby_datadir = "$tmp_check/data_standby_$$";
 
 # Define non-conflicting ports for both nodes.
 my $port_master  = $ENV{PGPORT};
diff --git a/src/test/perl/TestLib.pm b/src/test/perl/TestLib.pm
index 8eb27df796..641e864c1e 100644
--- a/src/test/perl/TestLib.pm
+++ b/src/test/perl/TestLib.pm
@@ -186,22 +186,25 @@ sub start_test_server
 	my ($tempdir) = @_;
 	my $ret;
 
-	print("### Starting test server in $tempdir\n");
+	# Assign test-related variables.  PID of the process running this
+	# script is assigned to the log file of the server to give uniqueness
+	# guarantee as this file's data is used for string comparison lookups.
+	$test_server_datadir = "$tempdir/pgdata";
+	$test_server_logfile = "$log_path/postmaster_$$.log";
+
+	print("### Starting test server in $tempdir, with logs in $test_server_logfile\n");
 	standard_initdb "$tempdir/pgdata";
 
 	$ret = system_log('pg_ctl', '-D', "$tempdir/pgdata", '-w', '-l',
-	  "$log_path/postmaster.log", '-o', "--log-statement=all",
+	  $test_server_logfile, '-o', "--log-statement=all",
 	  'start');
 
 	if ($ret != 0)
 	{
 		print "# pg_ctl failed; logfile:\n";
-		system('cat', "$log_path/postmaster.log");
+		system('cat', $test_server_logfile);
 		BAIL_OUT("pg_ctl failed");
 	}
-
-	$test_server_datadir = "$tempdir/pgdata";
-	$test_server_logfile = "$log_path/postmaster.log";
 }
 
 sub restart_test_server