func positionCmd(mysqld *mysqlctl.Mysqld, subFlags *flag.FlagSet, args []string) error {
	subFlags.Parse(args)
	if len(args) < 3 {
		return fmt.Errorf("Not enough arguments for position operation.")
	}

	pos1, err := myproto.DecodeReplicationPosition(args[1])
	if err != nil {
		return err
	}

	switch args[0] {
	case "equal":
		pos2, err := myproto.DecodeReplicationPosition(args[2])
		if err != nil {
			return err
		}
		fmt.Println(pos1.Equal(pos2))
	case "at_least":
		pos2, err := myproto.DecodeReplicationPosition(args[2])
		if err != nil {
			return err
		}
		fmt.Println(pos1.AtLeast(pos2))
	case "append":
		gtid, err := myproto.DecodeGTID(args[2])
		if err != nil {
			return err
		}
		fmt.Println(myproto.AppendGTID(pos1, gtid))
	}

	return nil
}

// writeRecoveryPosition will write the current GTID as the recovery position
// for the next transaction.
// We will also try to get the timestamp for the transaction. Two cases:
// - we have statements, and they start with a SET TIMESTAMP that we
//   can parse: then we update transaction_timestamp in blp_checkpoint
//   with it, and set SecondsBehindMaster to now() - transaction_timestamp
// - otherwise (the statements are probably filtered out), we leave
//   transaction_timestamp alone (keeping the old value), and we don't
//   change SecondsBehindMaster
func (blp *BinlogPlayer) writeRecoveryPosition(tx *proto.BinlogTransaction) error {
	now := time.Now().Unix()

	blp.blpPos.Position = myproto.AppendGTID(blp.blpPos.Position, tx.GTIDField.Value)
	updateRecovery := UpdateBlpCheckpoint(blp.blpPos.Uid, blp.blpPos.Position, now, tx.Timestamp)

	qr, err := blp.exec(updateRecovery)
	if err != nil {
		return fmt.Errorf("Error %v in writing recovery info %v", err, updateRecovery)
	}
	if qr.RowsAffected != 1 {
		return fmt.Errorf("Cannot update blp_recovery table, affected %v rows", qr.RowsAffected)
	}
	blp.blplStats.SetLastPosition(blp.blpPos.Position)
	if tx.Timestamp != 0 {
		blp.blplStats.SecondsBehindMaster.Set(now - tx.Timestamp)
	}
	return nil
}

//.........这里部分代码省略.........
			format, err = ev.Format()
			if err != nil {
				return pos, fmt.Errorf("can't parse FORMAT_DESCRIPTION_EVENT: %v, event data: %#v", err, ev)
			}
			continue
		}

		// We can't parse anything until we get a FORMAT_DESCRIPTION_EVENT that
		// tells us the size of the event header.
		if format.IsZero() {
			// The only thing that should come before the FORMAT_DESCRIPTION_EVENT
			// is a fake ROTATE_EVENT, which the master sends to tell us the name
			// of the current log file.
			if ev.IsRotate() {
				continue
			}
			return pos, fmt.Errorf("got a real event before FORMAT_DESCRIPTION_EVENT: %#v", ev)
		}

		// Strip the checksum, if any. We don't actually verify the checksum, so discard it.
		ev, _, err = ev.StripChecksum(format)
		if err != nil {
			return pos, fmt.Errorf("can't strip checksum from binlog event: %v, event data: %#v", err, ev)
		}

		// Update the GTID if the event has one. The actual event type could be
		// something special like GTID_EVENT (MariaDB, MySQL 5.6), or it could be
		// an arbitrary event with a GTID in the header (Google MySQL).
		if ev.HasGTID(format) {
			gtid, err = ev.GTID(format)
			if err != nil {
				return pos, fmt.Errorf("can't get GTID from binlog event: %v, event data: %#v", err, ev)
			}
			pos = myproto.AppendGTID(pos, gtid)
		}

		switch {
		case ev.IsGTID(): // GTID_EVENT
			if ev.IsBeginGTID(format) {
				begin()
			}
		case ev.IsXID(): // XID_EVENT (equivalent to COMMIT)
			if err = commit(ev.Timestamp()); err != nil {
				return pos, err
			}
		case ev.IsIntVar(): // INTVAR_EVENT
			name, value, err := ev.IntVar(format)
			if err != nil {
				return pos, fmt.Errorf("can't parse INTVAR_EVENT: %v, event data: %#v", err, ev)
			}
			statements = append(statements, proto.Statement{
				Category: proto.BL_SET,
				Sql:      fmt.Sprintf("SET %s=%d", name, value),
			})
		case ev.IsRand(): // RAND_EVENT
			seed1, seed2, err := ev.Rand(format)
			if err != nil {
				return pos, fmt.Errorf("can't parse RAND_EVENT: %v, event data: %#v", err, ev)
			}
			statements = append(statements, proto.Statement{
				Category: proto.BL_SET,
				Sql:      fmt.Sprintf("SET @@RAND_SEED1=%d, @@RAND_SEED2=%d", seed1, seed2),
			})
		case ev.IsQuery(): // QUERY_EVENT
			// Extract the query string and group into transactions.
			q, err := ev.Query(format)

// AppendGTID updates the current replication position by appending a GTID to
// the set of transactions that have been processed.
func (rci *RowcacheInvalidator) AppendGTID(gtid myproto.GTID) {
	rci.posMutex.Lock()
	defer rci.posMutex.Unlock()
	rci.pos = myproto.AppendGTID(rci.pos, gtid)
}