Goal

Server support zlib library for compression.
Facebook zstd (open-source dual BSD and GPLv2 license) argue to have better compression and decompression speed for better ratio.

MySQL implement that in 8.0.
see task , task, task and documentation

New variables

[Compression_algorithm|https://dev.mysql.com/doc/refman/8.0/en/server-status-variables.html#statvar_Compression_algorithm] : The name of the compression algorithm in use for the current connection to the server
[Compression_level|https://dev.mysql.com/doc/refman/8.0/en/server-status-variables.html#statvar_Compression_level]: The compression level in use for the current connection to the server
protocol_compression_algorithms: List the compression algorithms that the server permits for incoming connections.

Protocol change

New capability CLIENT_ZSTD_COMPRESSION_ALGORITHM (1UL << 26) indicate supporting zstd algorithm. (enable when global variable protocol-compression-algorithms contains zstd).

Handshake Response Packet has a new "compress_level" value

* int<4> client capabilities

* int<4> max packet size

* int<1> client character collation

* string<19> reserved

* if not (server_capabilities & CLIENT_MYSQL)

  * int<4> extended client capabilities

* else

  * string<4> reserved

* string<NUL> username

* if (server_capabilities & PLUGIN_AUTH_LENENC_CLIENT_DATA)

  * string<lenenc> authentication data

* else if (server_capabilities & CLIENT_SECURE_CONNECTION)

  * int<1> length of authentication response

  * string<fix> authentication response (length is indicated by previous field)

* else

  * int<1> 0x00

* if (server_capabilities & CLIENT_CONNECT_WITH_DB)

  * string<NUL> default database name

* if (server_capabilities & CLIENT_PLUGIN_AUTH)

  * string<NUL> authentication plugin name

* if (server_capabilities & CLIENT_CONNECT_ATTRS)

  * int<lenenc> size of connection attributes

  * loop

    * string<lenenc> key

    * string<lenenc> value

* if (server_capabilities & CLIENT_ZSTD_COMPRESSION_ALGORITHM && client_capabilities & CLIENT_ZSTD_COMPRESSION_ALGORITHM )

  * string<1> compression level

No dictionnary is used in MySQL implementation, but dictionary with zstd benchmarks generally improve encryption/decryption time drastically for small amount of data. Some verification might be done to see if that this can be applicable to MariaDB exchanges