$st = pack('dd', $st[0], $st[1]);
} while ($st ne $self->{st} && $tries++ < 3);
warn "W: $f: .st_dev, .st_ino unstable\n" if $st ne $self->{st};
- $dbh->do('PRAGMA synchronous = OFF') if ($rw // 0) > 1;
+
+ if ($rw) {
+ # TRUNCATE reduces I/O compared to the default (DELETE).
+ #
+ # Do not use WAL by default since we expect the case
+ # where any users may read via read-only daemons
+ # (-httpd/-imapd/-nntpd); but only a single user has
+ # write permissions for -watch/-mda.
+ #
+ # Read-only WAL support in SQLite 3.22.0 (2018-01-22)
+ # doesn't do what we need: it is only intended for
+ # immutable read-only media (e.g. CD-ROM) and not
+ # usable for our use case described above.
+ #
+ # If an admin is willing to give read-only daemons R/W
+ # permissions; they can enable WAL manually and we will
+ # respect that by not clobbering it.
+ my $jm = $dbh->selectrow_array('PRAGMA journal_mode');
+ $dbh->do('PRAGMA journal_mode = TRUNCATE') if $jm ne 'wal';
+
+ $dbh->do('PRAGMA synchronous = OFF') if $rw > 1;
+ }
$dbh;
}