capistrant opened a new pull request, #18844: URL: https://github.com/apache/druid/pull/18844
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Add new centralized storage for `CompactionState` where individual states can be looked up by the aforementioned fingerprint. Since it is common for many segments in a data source to share a single `CompactionState`, this greatly reduces the metadata storage overhead for storing compaction states. ##### Metadata Store Changes ###### `druid_segments` Add new column `compaction_state_fingerprint` that stores the fingerprint representation of the segments current compaction state. It can be `null` if no compaction has taken place. ###### `druid_compactionStates` New metadata table that stores the full `CompactionState` associated with a fingerprint. Segments can look up their full compaction state here by using the `compaction_state_fingerprint` that they are associated with. ##### `CompactionStateManager` The CompactionStateManager is responsible for managing the persistence and lifecycle of compaction states on the Coordinator. It stores unique compaction configurations (identified by fingerprints) in the metadata database and maintains a cache to optimize lookups. The manager tracks which compaction states are actively referenced by segments, marking unreferenced states as unused and periodically cleaning up old unused states. This fingerprinting approach allows Druid to efficiently store and retrieve compaction metadata without duplicating identical compaction configurations across multiple segments, while the cache layer minimizes database queries for frequently accessed compaction states. ###### `OnHeapCompactionStateManager` Meant to serve as a mechanism for testing and simulations where metadata persistence may not be available/needed #### Legacy `lastCompactionState` Roadmap This PR implements no automatic transition to fingerprints for segments who are compacted and store `CompactionState` in their `lastCompactionState` field. Instead this PR aims to continue supporting `lastCompactionState` in Compaction decision making for segments compacted before fingerprinting. This means that legacy segments **will not** have to be re-compacted simply because they are not fingerprinted, as long as they have the proper `CompactionState` as specified by the compaction configuration for the data source in question. This PR also continues to write both the new fingerprint as well as the legacy `lastCompactionState` by default. This allows normal rolling upgrade order as well as Druid version rollback without un-needed re-compaction. An operator can disable writing `lastCompactionState` by updating the cluster compaction config, after the Druid upgrade completes. Eventually, Druid code base will cease writing `lastCompactionState` at all and instead force using fingerprinting going forward. I think this should be done in the Druid version following the first version that this new feature is seen in. Even at this point, `lastCompactionState` will need to continue to be supported for already written segments, unless we want to devise an automated migration plan that can run in the background of a cluster to get all compacted segments migrated to fingerprinting. <!-- 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. --> #### Release note <!-- Give your best effort to summarize your changes in a couple of sentences aimed toward Druid users. If your change doesn't have end user impact, you can skip this section. For tips about how to write a good release note, see [Release notes](https://github.com/apache/druid/blob/master/CONTRIBUTING.md#release-notes). --> *coming soon* <hr> ##### Key changed/added classes in this PR * `CompactionStatus` * `CompactionConfigBasedJobTemplate` * `CompactionState` * `SQLMetadataConnector` * `CompactionStateManager` * `CompactSegments` * `KillUnreferencedCompactionState` <hr> <!-- Check the items by putting "x" in the brackets for the done things. 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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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