Description

Expands on the structures added in #10613 to add support for grouping on string expressions in the vectorized group by engine. The key addition that makes this possible is DictionaryBuildingSingleValueStringGroupByVectorColumnSelector, which is the vectorized group by engine version of DictionaryBuildingStringGroupByColumnSelectorStrategy, and allows the vector group by engine to group on strings which are not dictionary encoded.

To help showcase this, I added vectorization support to the concat operator string1 + 'foo', and the concat function concat(string1,'-',string2,'-',long1).

It provides a pretty decent performance increase. From the added benchmark queries:

      // 26: group by string expr with non-expr agg
      "SELECT CONCAT(string2, '-', long2), SUM(double1) FROM foo GROUP BY 1 ORDER BY 2",
      // 27: group by string expr with expr agg
      "SELECT CONCAT(string2, '-', long2), SUM(long1 * double4) FROM foo GROUP BY 1 ORDER BY 2"

Benchmark                        (query)  (rowsPerSegment)  (vectorize)  Mode  Cnt     Score    Error  Units
SqlExpressionBenchmark.querySql       26           5000000        false  avgt    5  1601.424 ± 22.075  ms/op
SqlExpressionBenchmark.querySql       26           5000000        force  avgt    5  1017.797 ± 18.384  ms/op
SqlExpressionBenchmark.querySql       27           5000000        false  avgt    5  2072.850 ± 46.369  ms/op
SqlExpressionBenchmark.querySql       27           5000000        force  avgt    5  1072.897 ± 19.756  ms/op

Vectorizing additional string expressions I will save for a future PR.

Key changed/added classes in this PR

• DictionaryBuildingSingleValueStringGroupByVectorColumnSelector
• VectorGroupByEngine
• GroupByVectorColumnProcessorFactory
• VectorStringProcessors
• StringOutMultiStringInVectorProcessor

This PR has:

• been self-reviewed.
• 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 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 is met.
• been tested in a test Druid cluster.