over+msgmap: respect WAL journal_mode if set

WAL actually seems to have ideal locking characteristics given
concurrency problems I'm experiencing with --reindex running
in parallel with expensive read-only SQLite queries:
<https://public-inbox.org/meta/20200825001204.GA840@dcvr/>

Unfortunately, we cannot blindly use WAL while preserving
compatibility with existing setups nor our guarantees that
read-only daemons are indeed "read-only".

However, respect an user's the choice to set WAL on their
own if they're comfortable with giving -nntpd/-httpd/-imapd
processes write permission to the directory storing SQLite DBs.

1 files changed, 0 insertions, 3 deletions

diff --git a/lib/PublicInbox/Msgmap.pm b/lib/PublicInbox/Msgmap.pm
index 5b4cebc1..d28e96c8 100644
--- a/lib/PublicInbox/Msgmap.pm
+++ b/lib/PublicInbox/Msgmap.pm
@@ -31,9 +31,6 @@ sub new_file {
         my $self = bless { filename => $f }, $class;
         my $dbh = $self->{dbh} = PublicInbox::Over::dbh_new($self, $rw);
         if ($rw) {
-                # TRUNCATE reduces I/O compared to the default (DELETE)
-                $dbh->do('PRAGMA journal_mode = TRUNCATE');
-
                 $dbh->begin_work;
                 create_tables($dbh);
                 $self->created_at(time) unless $self->created_at;