Add Throttle Support

[Xuanwo]

ThrottleLayer can help users to control the max bandwidth that used by OpenDAL.

[morristai]

Hi @Xuanwo, I'm interested in this issue, but I need more information. For example, is the goal to limit the amount of data that OpenDAL can send over the network in a given time period (e.g. set_write_timeout(10s)), or to limit the network speed at any given time (e.g. 100 kbps)?

[Xuanwo]

Thanks for your interest!

to limit the network speed at any given time (e.g. 100 kbps)?

This issue want to address this so that users can limit the bandwidth to 100Mbps and so on.

[morristai]

So I just did a quick survey of existing Rust crates. There are different kinds of bandwidth limit algorithms, the most common one being "Token Bucket", and another being "Leaky Bucket".

• For Token Bucket, there's TiKV async-speed-limit:
  tikv/async-speed-limit: Asynchronously speed-limiting multiple byte streams (But it seems to lack maintenance.)

• As for Leaky Bucket, this crate offers a similar algorithm(Generic Cell Rate Algorithm (GCRA)) to Leaky Bucket, but has a few advantages over most Leaky Bucket implementations: governor/README.md at master · antifuchs/governor · GitHub

Both seem to support asynchronous. Do we have any existing preferences?

[Xuanwo]

Thanks a lot for the research!

• As for Leaky Bucket, this crate offers a similar algorithm(Generic Cell Rate Algorithm (GCRA)) to Leaky Bucket, but has a few advantages over most Leaky Bucket implementations: governor/README.md at master · antifuchs/governor · GitHub

governor LGTM!

[morristai]

Thanks a lot for the research!

• As for Leaky Bucket, this crate offers a similar algorithm(Generic Cell Rate Algorithm (GCRA)) to Leaky Bucket, but has a few advantages over most Leaky Bucket implementations: governor/README.md at master · antifuchs/governor · GitHub

governor LGTM!

Sounds good. The governor supports two types of limiters: "direct" and "keyed".

• Direct rate limiters maintain a single state, such as the rate of outgoing email conversations.
• Keyed rate limiters, on the other hand, maintain a separate rate limiting state for each key. For example, they can be used to regulate the flow of API requests made by each customer.

Currently, I am unsure how to implement the Keyed Limiter as it requires interaction with the throttle layer state after building the Operator. Should I first try implementing the Direct Limiter, as all operations under an operator share an Atomic Limiter?

[Xuanwo]

Should I first try implementing the Direct Limiter, as all operations under an operator share an Atomic Limiter?

LGTM! And we don't need to implement keyed support until we have user's feature request.

[Xuanwo]

Mostly DONE! Thanks @morristai, we can polish this layer when new feature requested.