GWphua opened a new pull request, #17482: URL: https://github.com/apache/druid/pull/17482
Fixes #6647 ### Description This PR is built upon #6683 and #9172 and aims to reduce the number of ZooKeeper watch counts. #### Fixed Huge Number of Watches in ZooKeeper Previously, `Announcer.java` causes all child nodes under the parent path to be watched by the ZooKeeper ensemble. This causes an unnecessarily large number of ZooKeeper watches to be produced. The new `NodeAnnouncer.java` class, which is heavily modelled on the `Announcer.java`, aims to address this issue by announcing a single node within a ZooKeeper ensemble. By eliminating the watches on child nodes, this approach significantly reduces the total number of watch counts in ZooKeeper. Tests conducted on the production server also indicate a decrease in watch counts resulting from this change.  The original `Announcer.java` still provides better performance for segment announcements, and hence will be retained in the codebase. #### Documentation - Implementation of #6683 and #9172 are complete, and this PR addresses blocking requests for change by adding Javadocs, and making announcement logic more human-readable. - Remove [humor](https://github.com/apache/druid/pull/6683#discussion_r239161626) in error logs. #### Refactoring - Shift `Announceable` class in `Announcer.java` to `Announceable.java`. - Refactor long methods by creating helper functions. - Add `ZKPathsUtils.java` to abstract the retrieval of ZooKeeper path and ZooKeeper node. ### Further Actionable #### Deprecated Code The `PathChildrenCache`, `NodeCache` classes have been [deprecated](https://curator.apache.org/apidocs/org/apache/curator/framework/recipes/cache/package-summary.html) since Curator 5.0.0. We can look into replacing these deprecated classes with `CuratorCache`. CuratorCache requires ZooKeeper 3.6+, and we are currently using ZooKeeper 3.8.4. #### Concurrency Flow Add a concurrent control flow documentation for NodeAnnouncer. <!-- In each section, please describe design decisions made, including: - Choice of algorithms - Behavioral aspects. What configuration values are acceptable? How are corner cases and error conditions handled, such as when there are insufficient resources? - Class organization and design (how the logic is split between classes, inheritance, composition, design patterns) - Method organization and design (how the logic is split between methods, parameters and return types) - Naming (class, method, API, configuration, HTTP endpoint, names of emitted metrics) --> <!-- It's good to describe an alternative design (or mention an alternative name) for every design (or naming) decision point and compare the alternatives with the designs that you've implemented (or the names you've chosen) to highlight the advantages of the chosen designs and names. --> <!-- If there was a discussion of the design of the feature implemented in this PR elsewhere (e. g. a "Proposal" issue, any other issue, or a thread in the development mailing list), link to that discussion from this PR description and explain what have changed in your final design compared to your original proposal or the consensus version in the end of the discussion. If something hasn't changed since the original discussion, you can omit a detailed discussion of those aspects of the design here, perhaps apart from brief mentioning for the sake of readability of this PR description. --> <!-- Some of the aspects mentioned above may be omitted for simple and small changes. --> #### Release note Improved: ZooKeeper no longer spins up an unnecessary large number of watches when running realtime tasks. <hr> ##### Key changed/added classes in this PR * `Announcer.java` * `NodeAnnouncer.java` * `Announceable.java` * `AnnouncerModule.java` * `ZKPathsUtils.java` <hr> <!-- Check the items by putting "x" in the brackets for the done things. Not all of these items apply to every PR. Remove the items which are not done or not relevant to the PR. None of the items from the checklist below are strictly necessary, but it would be very helpful if you at least self-review the PR. --> This PR has: - [x] been self-reviewed. - [x] 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.) - [x] a release note entry in the PR description. - [x] added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links. - [x] added or updated version, license, or notice information in [licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md) - [x] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader. - [x] 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. - [x] been tested in a test Druid cluster. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
