hide & deprecate enable-streaming

[SunRunAway]

Feature Request

Is your feature request related to a problem? Please describe:

enable-streaming is not well maintained because we are focusing on optimizing the non-streaming coprocessor API for its performance and resource usage and don’t have time to optimize streaming's currently, I propose to deprecate it temporarily until somebody has time to pick it up again and prove it could be GA in the future.

Describe the feature you'd like:

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

see https://asktug.com/t/topic/37526/7

[SunRunAway]

/cc @zz-jason @breeswish

[zz-jason]

@SunRunAway could you link all the bugs that related to streaming API? Without seeing this bug list, it's hard to decide whether to deprecate it temporarily.

[SunRunAway]

See https://asktug.com/t/topic/37526 and https://asktug.com/t/topic/62984

[SunRunAway]

We are currently focusing on optimizing the non-streaming coprocessor API for its performance and resource usage, but when the users enable the steaming API, they will not be benefited from us.

[breezewish]

@zz-jason There are a lot of known trivial issues, for example,

1. TiKV known bug: Selection executor does not handle start_scan or stop_scan correctly tikv/tikv#3677 (won't fix)
2. TiKV does not handle streaming scan efficiently
3. Coprocessor Cache does not work in streaming
4. The runtime statistics in streaming mode is not correct. The newly added ScanDetailV2 may be incorrect as well.
5. When I reviewed the Coprocessor part in TiDB I found that it may not correctly handle the case that partial result is lost and request is retried. There is no test case for this either.

In summary, the streaming API seems to be not complete and not efficient. There is no plan to optimize. Tests may not completely covered as well.

[zz-jason]

@breeswish got it, thanks.