[issue #752] replace go-rate rate limiter with a buffered channel implementation

[zzzming]

Fixes #752

Motivation

The go rate limiter library, beefsack/go-rate, is an MIT license. We need update the license. The PR removes this dependency.

Modifications

In Go, it is rather simple to implement a rate limiter directly. A buffered channel is used to store a request timestamp as message. The channel receiver check each timestamp (in the message) to sleep on the remaining time duration.

The per second rate is the size of channel buffer. If the buffer is full, the main producing go routine blocks on producing Pulsar message, until the sleep expires and move to on the next message in the channel thus free up a slot in the channel.

It resembles leaky bucket rate limiting implementation. Because of leveraging go channel, it uses less than 10 lines of code and remove the dependency entirely. Since the implementation only uses one buffered channel, avoid using expensive mutex lock/unlocking and a list by the original library implementation.

Verifying this change

Since the change only affects the perf utility, I built the tool and verify the producing rate is accurate.

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): (yes)
  Removes beefsak/go-rate dependency
• The public API: ( no)
• The schema: (no)
• The default values of configurations: (no)
• The wire protocol: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable / docs / GoDocs / not documented)
• If a feature is not applicable for documentation, explain why?
• If a feature is not documented yet in this PR, please create a followup issue for adding the documentation

[pgier]

I like the idea of removing the dependency, just left a few in-line comments.

[pgier]

Since the buffer size here is proportional to the rate, should there be a limit on the max size? Is there a way to do this with a fixed buffer size?

[zzzming]

The buffer size is the rate per second. It is a leaky bucket rate limiter implementation. So the channel buffer should hold the same number of rate allowed.

[merlimat]

The MIT license is perfectly fine to be used here: https://www.apache.org/legal/resolved.html#category-a

The problem in that issue was to upgrade to a version with MIT license (old license was GPL).

[pgier]

@merlimat I think the idea @zzzming had was that removing the dependency also solves the license issue, and it's about the same amount of code anyway.