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Posted to commits@druid.apache.org by GitBox <gi...@apache.org> on 2021/07/29 23:58:09 UTC
[GitHub] [druid] jihoonson opened a new pull request #11517: Fix incorrect result of exact topN on an inner join with limit
jihoonson opened a new pull request #11517:
URL: https://github.com/apache/druid/pull/11517
### Description
The topN engine can have an optimization that avoids computing unnecessary keys that cannot be included in the final result. When `useApproximateTopN` is unset, this optimization can be used when these 2 conditions are met.
- The query should not have filters.
- The interval of storageAdapter should match to that of the query.
[This `if` clause](https://github.com/apache/druid/blob/master/processing/src/main/java/org/apache/druid/query/topn/BaseTopNAlgorithm.java#L317-L321) checks whether this optimization is possible, but currently has a bug that it does not check whether the storageAdapter can built-in filters. For example, when the storageAdapter is a `HashJoinSegmentStorageAdapter`, its cursor may return a less number of unique values because of the join condition. Because this check is currently missing, the topN on an inner join can use the optimized path which effectively applies the limit before computing join, which in turn causing incorrect query result. This PR adds a new method, `hasBuiltInFilters`, in `StorageAdapter` to fix this bug.
<hr>
##### Key changed/added classes in this PR
* `StorageAdapter`
* `HashJoinSegmentStorageAdapter`
<hr>
This PR has:
- [x] 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.
- [x] 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.
- [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.
- [ ] added integration tests.
- [ ] been tested in a test Druid cluster.
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[GitHub] [druid] jihoonson merged pull request #11517: Fix incorrect result of exact topN on an inner join with limit
Posted by GitBox <gi...@apache.org>.
jihoonson merged pull request #11517:
URL: https://github.com/apache/druid/pull/11517
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[GitHub] [druid] jihoonson commented on pull request #11517: Fix incorrect result of exact topN on an inner join with limit
Posted by GitBox <gi...@apache.org>.
jihoonson commented on pull request #11517:
URL: https://github.com/apache/druid/pull/11517#issuecomment-890413590
@jon-wei Thanks for the review.
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