} elseif ( $dataSnapshotLag > self::MAX_READ_LAG ) {
            // Case B: high snapshot lag
            $pregenSnapshotLag = ( $walltime !== null ) ? ( $dataSnapshotLag - $walltime ) : 0;
            if ( ( $pregenSnapshotLag + self::GENERATION_HIGH_SEC ) > self::MAX_READ_LAG ) {
                // Case B1: generation started when transaction duration was already long