Join context hints

[adarshsanjeev]

Rebased and addressed some issues of #17406

Currently, using the query context, all joins in a query can be hinted to either broadcast or sort merge join. However, this does not allow this to be set at a join level.

Add support for hints to queries, which can dictate the join type.

Syntax

select /*+ sort_merge */ w1.cityName, w2.countryName
from
(
  select /*+ broadcast */ w3.cityName AS cityName, w4.countryName AS countryName from wikipedia w3 LEFT JOIN wikipedia-set2 w4 ON w3.regionName = w4.regionName
) w1
JOIN wikipedia-set1 w2 ON w1.cityName = w2.cityName
where w1.cityName='New York';

Note
Calcite does not expose if the hint is at a particular join level, and allows inheritance of hints from parent nodes. This causes join hints to to affect inner queries. Additional join hints can be added to inner queries as a workaround.

---

This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• a release note entry in the PR description.
• 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
• 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.
• added integration tests.
• been tested in a test Druid cluster.

[kgyrtkirk]

nit: is it really needed to burn in the "broadcast" literal here?

[kgyrtkirk]

note: I think this class should be moved in the DruidHints or something class you rename/restructure the JoinHint class to

[adarshsanjeev]

Changed to the enum name instead.

[kgyrtkirk]

this assumes that all hints are joinhints - which may not be true in the future

[adarshsanjeev]

Added a check here

[kgyrtkirk]

I think it would be better to not have this as an enum - and you could probably use as(JoinAlgorithm.class) or asJoinAlgorithm() to obtain the current value

[adarshsanjeev]

There's an issue with that, Calcite only seems to accept certain keywords as hints, and this is sort_merge. Trying to replace the hint name with sortMerge seems to make it not read by calcite.

[kgyrtkirk]

I don't think this should be serializable by jackson; if it gets on the wire it should be a JoinAlgorithm already

[adarshsanjeev]

I think it might have been to deserializer it for the planner context at some point

[kgyrtkirk]

I don't think there is meaning of this in this context as this engine doesn't support joinalgorithms ; so this change should be absent here or null ?

maybe use JsonInclude.Include.NON_NULL and make the class behave like null means BROADCAST ?