func isValidSeq(lg *zap.Logger, names []string) bool {
	var lastSeq uint64
	for _, name := range names {
		curSeq, _, err := parseWALName(name)
		if err != nil {
			if lg != nil {
				lg.Panic("failed to parse WAL file name", zap.String("path", name), zap.Error(err))
			} else {
				plog.Panicf("parse correct name should never fail: %v", err)
			}
		}
		if lastSeq != 0 && lastSeq != curSeq-1 {
			return false
		}
		lastSeq = curSeq
	}
	return true
}
func isValidSeq(lg *zap.Logger, names []string) bool {
	var lastSeq uint64
	for _, name := range names {
		curSeq, _, err := parseWALName(name)
		if err != nil {
			if lg != nil {
				lg.Panic("failed to parse WAL file name", zap.String("path", name), zap.Error(err))
			} else {
				plog.Panicf("parse correct name should never fail: %v", err)
			}
		}
		if lastSeq != 0 && lastSeq != curSeq-1 {
			return false
		}
		lastSeq = curSeq
	}
	return true
}
// names should have been sorted based on sequence number.
// isValidSeq checks whether seq increases continuously.