lib/PublicInbox/Msgmap.pm | 1 +

diff --git a/lib/PublicInbox/Msgmap.pm b/lib/PublicInbox/Msgmap.pm
index c85e7796cbd4512f2c286628a4eff8f04aed9388..eee8d6ca58b96adbb46746c1c23c848154ee804c 100644
--- a/lib/PublicInbox/Msgmap.pm
+++ b/lib/PublicInbox/Msgmap.pm
@@ -248,6 +248,7 @@ 	$self->{pid} or die 'BUG: not a temporary clone';
 	$self->{dbh} and die 'BUG: tmp_clone dbh not prepared for parent';
 	defined($self->{filename}) or die 'BUG: {filename} not defined';
 	$self->{dbh} = PublicInbox::Over::dbh_new($self, 2);
+	$self->{dbh}->do('PRAGMA journal_mode = MEMORY');
 }
 
 sub atfork_prepare {