jasonk000 opened a new pull request #12109:
URL: https://github.com/apache/druid/pull/12109
### Description
Following from #12105 with 1-20% CPU in `DimensionDictionary`, there are
some improvements to be made to the `add()` path on the
`StringDimensionIndexer`.
There are three sub-changes:
#### Introduce a new benchmark
`StringDimensionIndexerProcessBenchmark` in
cff7a6caaab2d28218ab01655c44d24e99c40e0c covers the `StringDimensionIndexer`
`processRowValsToUnsortedEncodedKeyComponent` for throughput.
#### Optimise `StringDimensionIndexer` -> `DimensionDictionary` boundary
in 400f0a5137264d9c4f0a88dc346b6730458b1b09 introduce an `AddResult` class
to combine the result of both (a) what is the index of the result, and (b) was
the result a new addition or refers to a previous element.
This results in a ~30% improvement on this codepath single threaded, and
~70% by bypassing multiple `size()` calls to determine whether the dictionary
has changed.
#### Switch lock implementation in `DimensionDictionary` to `StampedLock`
In aea89f5c502317b69957fbf592d84e4e9ee3f9a5 introduce improved concurrency
under multiple-reader scenarios, and scenarios where `add()` of existing
elements. Results in 3x improvement in contended situation.
#### Refactor
Slight refactor in 3e5c410047a74b3cae8044070260384803a2e1e5 to simplify flow
in `StringDimensionIndexer`.
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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.)
- [ ] 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)
- [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.
- [ ] added integration tests.
- [ ] been tested in a test Druid cluster. -> nb: partly, have not tested
`StampedLock` in prod
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