Support mysql protocol compression

[xqinghu]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

Release Version: v4.0.0
Edition: Community
Git Commit Hash: 689a6b6
Git Branch: heads/refs/tags/v4.0.0
UTC Build Time: 2020-05-28 01:37:40
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false

[morgo]

It looks like TiDB parses but ignores the compression set option. i.e.
https://github.com/pingcap/tidb/blob/master/server/conn_stmt.go#L614-L635

The parser can handle it, the const is ClientCompress. But a grep of server/* shows it is not present.

[bb7133]

Hi @xqinghu ,compression is not supported by TiDB(there's no plan for it before).

I'm going to change your issue for 'bug' to 'feature request', FYI.

[dveeden]

I looked at the compressed protocol in 2016 to implement part of this in Wirshark: https://code.wireshark.org/review/#/c/14603/

I don't think it would be very difficult to implement this for TiDB. However I don't think the compressed protocol is very useful, so I don't think this is a high priority issue. But please add a detailed description if anyone things this would make a real improvement for their usecase.

[dveeden]

https://dev.mysql.com/doc/dev/mysql-server/latest/page_protocol_basic_compression.html does have the docs for this.

There seems to be a new flag for zstandard compression.

[dveeden]

It looks like the Go MySQL driver doesn't support compression: go-sql-driver/mysql#24
This makes this difficult for unittesting and means tools like dumpling etc might not be able to take advantage of this. So if we implement this we should try to contribute support for this to the driver as well.

[xqinghu]

The bottleneck of ETL extraction task is bandwidth (1g), and the CPU is very idle, client is Java. Thanks @dveeden