--- a/src/test/recovery/t/049_wait_for_lsn.pl
+++ b/src/test/recovery/t/049_wait_for_lsn.pl
@@ -7,6 +7,19 @@
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
 use Test::More;
+use Time::HiRes qw(time);
+{
+ no warnings 'redefine';
+ my $orig = \&PostgreSQL::Test::Cluster::safe_psql;
+ *PostgreSQL::Test::Cluster::safe_psql = sub {
+  my $start = time();
+  my $ret = $orig->(@_);
+  my $q = $_[2]; $q =~ s/\s+/ /g;
+  note(sprintf("TIMING %.3f %s %s", time()-$start, $_[0]->name, substr($q,0,150)));
+  return $ret;
+ };
+}
+
 
 # Helper functions to control walreceiver for testing wait conditions.
 # These allow us to stop WAL streaming so waiters block, then resume it.
@@ -519,6 +532,10 @@
 my $mixed_target_lsn =
   $node_primary->safe_psql('postgres', "SELECT pg_current_wal_insert_lsn()");
 
+diag("WAL_LAYOUT_TARGET after $mixed_target_lsn");
+system('cp', '-R', $node_primary->data_dir . '/pg_wal', '/tmp/pg-wait-investigation/layout-after-wal') == 0
+  or die "could not preserve WAL: $!";
+
 # Start 6 waiters: 2 for each mode
 my @mixed_sessions;
 my @mixed_modes = ('standby_replay', 'standby_write', 'standby_flush');