[CCB] | MultiClientCommitTimestampGetter refactor - part 2

[sudiksha27]

Goals (and why):
Atlas should be able to accept a common batcher for getCommitTimestamps requests for multiple clients.

Implementation Description (bullets):

• Implements AutoBatcher capable of handling getCommitTimestamps requests for multiple clients
• The model is very close to the origin model - for each namespace, while all requests cannot be served, we batch all the requests together, try to do getCommitTimestamps in one call to the server & update the cache after receiving the response.
• The LockWatchEventCache#lastKnownVersion is fetched before making request to TimeLock and LockWatchEventCache#processGetCommitTimestampsUpdate is invoked as response is received.
• We try to serve requests as responses become available instead of waiting for all responses to serve all requests in one go.
• In case of exception, all pending requests are cancelled.
• This PR actually does not change the current flow
• I haven't done the wiring yet as the PR is pretty big already

Testing (What was existing testing like? What have you done to improve it?):
Added tests

Concerns (what feedback would you like?):

• There is code duplication b/w NamespacedBatchStateManager#process and BatchingCommitTimestampGetter#process but I could not think of a way of refactoring without 1. adding another iteration over request list 2. creating new instances of a suitable DS
• Did I miss/ break something horribly?

Where should we start reviewing?:
MultiClientCommitTimestampGetter

Priority (whenever / two weeks / yesterday):
Before EOD tomorrow is the dream

[changelog-app]

Generate changelog in changelog/@unreleased

Type

• Feature
• Improvement
• Fix
• Break
• Deprecation
• Manual task
• Migration

Description

AtlasDb client can now batch getCommitTimestamps requests across namespaces.

Check the box to generate changelog(s)

• Generate changelog entry

[jeremyk-91]

🕐 0:45 🏁 0:58

The core logic does look equivalent to a valid parallel execution of the current BatchingCommitTimetsampGetters. My comments here are largely around factoring.

[jeremyk-91]

👍 looks good, thanks for fixing all the comments!

[jeremyk-91]

❤️