capistrant opened a new pull request #11135: URL: https://github.com/apache/druid/pull/11135
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This allows the operator to limit the amount of work loading non-primary replicas that `RunRules` will execute in a single run. An example of a reason to use a non-default value for this new config is if the operator wants to ensure that major events such as historical service(s) leaving the cluster, large ingestion jobs, etc. do not cause an abnormally long `RunRules` execution compared to the cluster's baseline runtime. **Example** cluster: 3 historical servers in _default_tier with 18k segments per server. Each segment belongs to a datasource that has the load rule "LoadForever 2 replicas on _default_tier". The cluster load status is 100% loaded. Event: 1 historical drops out of the cluster. Today: The coordinator will load all 18k segments that are now under-replicated in a single execution of RunRules (as long as Throttling limits are not hit and there is capacity) My change: The coordinator can load a limited number of these under-replicated segments IF the operator has tuned the new dynamic config down from its default. For instance, the operator could say that it is 2k. Meaning it would take at least 9 coordination cycles to fully replicate the segments that were on the recently downed host. **Why** Operators need to balance lots of competing needs. Having the cluster fully replicated is great for HA. But if an event causes the coordinator to take 20 minutes to fully replicate because it has to load thousands of replicas, we sacrifice the timeliness of loading newly ingested segments that were inserted into the metastore after this long coordination cycle started. Maybe the operator cares more about that fresh data timeliness than the replication status, so they change the new config to a value that causes RunRules to take less time but require more execution cycles to bring the data back to full replication. Really what the change aims to do is give an operator more flexibility. As written the default would give the operator the exact same functionality that they see today. <!-- 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) --> **Design** I folded this new configuration and feature into ReplicationThrottler. That is essentially what it is doing, just in a new way compared to the current ReplicationThrottler functionality. <!-- 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. --> <hr> ##### Key changed/added classes in this PR * `CoordinatorDynamicConfig` * `ReplicationThrottler` * `RunRules` * `LoadRule` <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: - [ ] 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. - [ ] 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. -- 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. 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