[Feature Request] Inner queries for has_parent and has_child should be eligible for caching in the query cache

[jhinch-at-atlassian-com]

Is your feature request related to a problem? Please describe

GlobalOrdinalsQuery which is used by has_parent and has_child queries is not eligible for query caching as it makes use of global ordinals and so isn't segment cacheable. However its inner query should be as it doesn't use the global ordinals but currently isn't due to HasChildQueryBuilder.LateParsingQuery not propagating the query cache to the IndexerSearcher used for the inner query.

Describe the solution you'd like

Allow for the inner query to be cached, improving performance of join queries

Related component

Search:Performance

Describe alternatives you've considered

No response

Additional context

No response

[kkewwei]

It makes sense to me. As long as the query frequency is high, inner query to be cached.

[sandeshkr419]

@kkewwei @msfroh - Do you guys have any findings here?

[msfroh]

I agree with @kkewwei that it makes sense to cache them.

I see this line that explicitly disables the query cache on the newly-created IndexSearcher, which looks intentional, though:

OpenSearch/modules/parent-join/src/main/java/org/opensearch/join/query/HasChildQueryBuilder.java

Line 427 in a59ae3c

indexSearcher.setQueryCache(null);

I don't really understand why that was done and git blame shows that line coming from a merge commit, so it will take some more digging to understand the reasoning.

@jhinch-at-atlassian-com -- it sounds like you have an idea of how/where to propagate the cache. Do you want to give this issue a shot?