[PATCH 2/8] imaptracker: preserve WAL journal_mode if set by user

[Eric Wong <e@yhbt.net>]

It's no problem for most users to enable WAL, here, since
there's only a single process doing both reading and writing
(unlike the read-only daemons).  However, WAL doesn't work on
network filesystems, so it can't be enabled by default.
---
 lib/PublicInbox/IMAPTracker.pm | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/lib/PublicInbox/IMAPTracker.pm b/lib/PublicInbox/IMAPTracker.pm
index 102a74ce..92f21584 100644
--- a/lib/PublicInbox/IMAPTracker.pm
+++ b/lib/PublicInbox/IMAPTracker.pm
@@ -29,7 +29,12 @@ sub dbh_new ($) {
 		sqlite_use_immediate_transaction => 1,
 	});
 	$dbh->{sqlite_unicode} = 1;
-	$dbh->do('PRAGMA journal_mode = TRUNCATE');
+
+	# TRUNCATE reduces I/O compared to the default (DELETE).
+	# Allow and preserve user-overridden WAL, but don't force it.
+	my $jm = $dbh->selectrow_array('PRAGMA journal_mode');
+	$dbh->do('PRAGMA journal_mode = TRUNCATE') if $jm ne 'wal';
+
 	create_tables($dbh);
 	$dbh;
 }