[GitHub] [druid] clintropolis opened a new pull request, #13781: fix array_agg to work with complex types and bugs with expression aggregator complex array handling

[via GitHub]

clintropolis opened a new pull request, #13781:
URL: https://github.com/apache/druid/pull/13781

   ### Description
   This PR removes an overly restrictive validation check on `ARRAY_AGG` which 
was preventing use with druid `COMPLEX` types, such as `COMPLEX<json>`. This 
check is a relic from when this function was added, which was before the native 
expression system supported `COMPLEX` types.
   
   After removing this check, I ran into a couple of rough edges, and a bug in 
`ObjectStrategyComplexTypeStrategy`, which was missing a check to ensure that 
the positional `read` method actually moved the buffer position forward by the 
number of bytes read (useful for array_agg which is serializing arrays) instead 
of relying on the underlying `ObjectStrategy` to move the buffer.
   
   After the bugs, the result seems pretty useful, particularly for 
`COMPLEX<json>` (though certainly not the speediest thing around since its 
implemented as an expression aggregator):
   <img width="1239" alt="Screenshot 2023-02-09 at 3 06 39 AM" 
src="https://user-images.githubusercontent.com/1577461/217799893-09b463bb-6ade-4c5f-a39c-a86ad4f97d9b.png";>
   even distinct works:
   
   <img width="1236" alt="Screenshot 2023-02-09 at 3 06 05 AM" 
src="https://user-images.githubusercontent.com/1577461/217799943-bb01eccb-8242-48ec-acf1-026ebbad3650.png";>
   
   
   This PR has:
   
   - [x] been self-reviewed.
   - [ ] a release note entry in the PR description.
   - [ ] 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.
   - [x] been tested in a test Druid cluster.
   


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