feat: support read throttling by size

[Smityz]

Ref: apache/incubator-pegasus#830

[levy5307]

I think you can add some unit tests for rpc_holder

[hycdong]

I suggest splitting this pull request into 3 parts:

1. update with rpc_holder, and add unit test for it.
2. add token_bucket_throttling_controller
3. add other logic related with read size throttling

Besides, I notice that you implement token_bucket_throttling_controller under utils folder, but token_bucket_throttling_controller contains logic related with read size, such as function validate, variety _partition_count etc.
If the token_bucket_throttling_controller is a util class, it is supposed NOT contain content about its upper logic, otherwise, it is not suitable under util folder.

[Smityz]

I suggest splitting this pull request into 3 parts:

1. update with rpc_holder, and add unit test for it.
2. add token_bucket_throttling_controller
3. add other logic related with read size throttling

Besides, I notice that you implement token_bucket_throttling_controller under utils folder, but token_bucket_throttling_controller contains logic related with read size, such as function validate, variety _partition_count etc. If the token_bucket_throttling_controller is a util class, it is supposed NOT contain content about its upper logic, otherwise, it is not suitable under util folder.

which folder do you suggest?

[hycdong]

I suggest splitting this pull request into 3 parts:

1. update with rpc_holder, and add unit test for it.
2. add token_bucket_throttling_controller
3. add other logic related with read size throttling

Besides, I notice that you implement token_bucket_throttling_controller under utils folder, but token_bucket_throttling_controller contains logic related with read size, such as function validate, variety _partition_count etc. If the token_bucket_throttling_controller is a util class, it is supposed NOT contain content about its upper logic, otherwise, it is not suitable under util folder.

which folder do you suggest?

I recommend implement common utility under utils or utility folder, logic related to replica in replication_app_base to let storage module got it.

[Smityz]

The interface refers to https://github.com/XiaoMi/rdsn/blob/master/src/utils/throttling_controller.h
And I also have a plan to use token_bucket_throttling_controller to replace the original one.

[GiantKing]

Move _reject_task_counter up to "incubator-pegasus: src/server/pegasus_server_impl.cpp", and increase this counter while return “ERR_BUSY”.

[Smityz]

has merged split prs