kfaraz opened a new pull request, #17828:
URL: https://github.com/apache/druid/pull/17828
### Description
The `giant` lock in `TaskQueue` is acquired when performing any update or
read operation, such as:
- add a task
- remove a task
- read the list of tasks
- sync from storage
On large clusters with several concurrent tasks, this can become a
bottleneck.
This patch attempts to improve the concurrency in `TaskQueue` by using a
concurrent hash map instead.
### Changes
- Use a `ConcurrentHashMap` to track active tasks. The locking was needed
only to handle
competing updates are not made to the _same_ task ID. This can be handled by
a `ConcurrentHashMap` too.
- Perform any update on the entry for a task ID within
`ConcurrentHashMap.compute` to ensure atomicity
- Convert the `giant` lock from a `ReentrantLock` to a
`ReentrantReadWriteLock`
- Use `giant` lock to ensure that the `TaskQueue` `start` and `stop` is
mutually exclusive from any other
normal operation on the `TaskQueue`
- Keep a `lastUpdatedTime` in every `TaskEntry` to handle race conditions
when syncing from metadata store
#### Handling race conditions
### Pending
- Unit tests for concurrency
- Cluster testing
<hr>
This PR has:
- [ ] been self-reviewed.
- [ ] using the [concurrency
checklist](https://github.com/apache/druid/blob/master/dev/code-review/concurrency.md)
(Remove this item if the PR doesn't have any relation to concurrency.)
- [ ] added documentation for new or modified features or behaviors.
- [ ] a release note entry in the PR description.
- [ ] added Javadocs for most classes and all non-trivial methods. Linked
related entities via Javadoc links.
- [ ] added or updated version, license, or notice information in
[licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md)
- [ ] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [ ] added unit tests or modified existing tests to cover new code paths,
ensuring the threshold for [code
coverage](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md)
is met.
- [ ] added integration tests.
- [ ] been tested in a test Druid cluster.
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