capistrant opened a new pull request, #12615: URL: https://github.com/apache/druid/pull/12615
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Don't reference the issue in the title of this pull-request. --> <!-- If you are a committer, follow the PR action item checklist for committers: https://github.com/apache/druid/blob/master/dev/committer-instructions.md#pr-and-issue-action-item-checklist-for-committers. --> ### Description <!-- Describe the goal of this PR, what problem are you fixing. If there is a corresponding issue (referenced above), it's not necessary to repeat the description here, however, you may choose to keep one summary sentence. --> <!-- Describe your patch: what did you change in code? How did you fix the problem? --> <!-- If there are several relatively logically separate changes in this PR, create a mini-section for each of them. For example: --> #### Modified the deserialization of DynamicCoordinatorConfig The coordinator now uses the `DynamicCoordinatorConfig.Builder.class` for deserialization of the dynamic coordinator config. This allows us to automatically use the Builder specified default for a configuration key that does not exist in the metastore payload for the dynamic config. Doing so ensures that an "incomplete" config in the metastore will be supplemented with the proper Druid specified defaults every time it is deserialized. Prior to this change, Druid used `DynamicCoordinatorConfig.class` directly for deserialization. The drawback on this is that `DynamicCoordinatorConfig` is less equipped for cleanly handling missing configuration keys during deserialization. If a developer used a Java primitive when adding a new config, on upgrade, the deserialization would use the Java system default for a missing value. This is often times very bad! For instance, I might add `newIntConfig` to Druid. Since this isn't in the previous version of Druid, upgrading the coordinator would cause deserialization of the legacy config to populate newIntConfig with the value `0`. But as a developer, I needed `newIntConfig` to default to 100. To work-a-round this, I would flip the type to `Integer` which would deserialize a missing value as `null`. I could then check for this null value in the constructor and replace it with the desired default from the Builder class constants. You can see a more realistic example of this work -a-round [here](https://github.com/apache/druid/commit/bb3c810b368f2f49d33d24df38b078640d7d38d4#diff-3119db307661e92f88879f6465bfa3229f9e5c8cce0fa11c9487b2d7ded87fd7R140) Another reference to this conditional null check comes up in [this](https://github.com/apache/druid/pull/12504#discussion_r887380372) thread. My change gets us away from this pattern. We are catching an undesirable state and deferring to the default in the Builder class already... so why not just use the Builder for deserialization is my thought. This way we can leverage the built in patterns for handling nulls and replacing them with constant defaults there instead of the `DynamicCoordinatorConfig` My one worry is that I am missing an angle here that required us to forgo the Builder for this deserialization. At first instance, I figured that serialization used the same `ConfigManager` watcher and that using the builder for serde would cause issues in writing the config. However, this does not seem to be the case after running automated tests, manual review of the config update code path, and testing this change in my local druid cluster. Still, perhaps I am overlooking something that has prevented us from using the builder. That is what I'm hoping the review process can smoke out. #### What I did not touch in this PR I did not alter any of the code in the `CoordinatorDynamicConfig` constructor that is performing the deserialization work-a-round that my update is intended to prevent. I could certainly make that change here as well, but I wanted to be conservative with the scope of this change and guarantee no change in behavior of existing code. Removing the conditional checks on null and changing the variables to primitive types would change behavior IF there were any use of the `CoordinatorDynamicConfig` constructor directly. To my knowledge, unit tests are the only place this still happens. <!-- In each section, please describe design decisions made, including: - Choice of algorithms - Behavioral aspects. What configuration values are acceptable? 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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. --> <hr> ##### Key changed/added classes in this PR * `CoordinatorDynamicConfig` <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] added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links. - [X] been tested in a test Druid cluster. -- This is an automated message from the Apache Git Service. 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