readme_retaindir.diff

diff --git a/src/test/perl/README b/src/test/perl/README
index d62db9b5d8..b02e1ffc3d 100644
--- a/src/test/perl/README
+++ b/src/test/perl/README
@@ -23,6 +23,11 @@ tmp_check/log/ to get more info.  Files named 'regress_log_XXX' are log
 output from the perl test scripts themselves, and should be examined first.
 Other files are postmaster logs, and may be helpful as additional data.
 
+Data directories will also be left behind for analysis when a test fails,
+and are named according to the test filename.  When the environment variable
+PG_TEST_NOCLEAN is set, data directories will be retained regardless of test
+status.
+
 
 Writing tests
 -------------