clintropolis opened a new pull request #11829:
URL: https://github.com/apache/druid/pull/11829
### Description
Currently, Druid only supports `STRING` typed dictionary encoded columns,
which are currently necessary to support utilizing bitmap indexes for fast
filtering, meaning that only `STRING` columns can be indexed in this manner.
However, there is a lot of structure that isn't really specific to `String`
types that can be extracted, so this PR begins this process of pulling out
common structure to make generic so that someday we can support additional
types of dictionary encoded columns, including `LONG` and even `COMPLEX`.
The changes in this PR should be limited to moving stuff around and the
occasional change of `String` to some generic parameter, and most of the code
has been pulled out of either `StringDimensionIndexer` or
`StringDimensionMergerV9`.
I believe that there is probably additional methods which could be pushed
down, particularly for the `DictionaryEncodedColumnIndexer` such as dimension
selector creation, but I have not done it at this time.
Additionally, i have removed `IndexSeeker` from `IndexMerger` since it was
duplicated in `StringDimensionMergerV9` and not used anywhere.
<hr>
##### Key changed/added classes in this PR
* `DictionaryEncodedColumnIndexer`
* `DictionaryEncodedColumnMerger`
* `DictionaryMergingIterator`
* `DimensionDictionary`
* `SortedDimensionDictionary`
* `StringDimensionIndexer`
* `StringDimensionMergerV9`
<hr>
This PR has:
- [x] been self-reviewed.
- [x] 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.
- [x] 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.
- [x] been tested in a test Druid cluster.
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