Address reprint: https://dev.mysql.com/doc/dev/mysql-server/8.0.0/page_protocol_basic_packets.html
A, packet meaning
packet is not the mysql procotol (agreement), but how accurate data protocol data transmission protocol and even how long split more underlying support.
Two, packet structure
| length(3-bytes) | sequence-id(1-byte) | payload(length-bytes) |
length: length in bytes of the payload
sequence-id: packet sequence number of each new mysql command resets to 0, the long protocol data, will be split into a plurality of Packet, are sequentially specified by the order of the sequence-id
payload: Actual procotol (protocol) data, is less than 16M, then the entire protocol payload is command data, or the data will be split into a plurality of packet procotol
Three, packet limit
1. A packet transmission maximum energy 16MB, i.e., the data protocol is less than 16MB, you may transmit a complete packet
2. If the packet is greater than 16MB, will split, the split will be as follows, i.e., a plurality of split except the last, will be before ff ff ff, until it encounters less than ff ff ff, and sequence-id, will The final assembly procotol protocol data as the basis for:
ff ff ff 00 .......
00 00 00 01 .....
Four, mysql server source code handler inlet
1. interested in looking at the code words, a complete packet of data reading and to a plurality of packet assembling function
[SQL / net_serv.cc]: ulong my_net_read (the NET * NET), as shown below:
Examples of protocol V. Analysis of mysql
After finished reading all the Packet, and assembled into the final protocol protocol data, it can be read payload area of the data relating to the internal protocol
protocol data structure:
| cmd(1-byte) | payload(length - 1 bytes) |
cmd: protocol commands the actual agreement, including:
payload: the data structure will in particular cmd
As to COM_INIT_DB (such as the use use DBName instructions):
Its cmd is 02, payload (dbname) as String [ EOF ]:
Possible complete Packet :
0500 00 00 02 74 65 73 74
length : 5
sequence-id: 0
cmd : 02(COM_INIT_DB)
db_name : 0x74 0x65 0x73 0x74
Reprinted related links:
https://dev.mysql.com/doc/internals/en/text-protocol.html
https://dev.mysql.com/doc/internals/en/com-init-db.html
