[jira] [Updated] (LUCENE-6590) Explore different ways to apply boosts

["Adrien Grand (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCENE-6590?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Adrien Grand updated LUCENE-6590:
---------------------------------
    Attachment: LUCENE-6690.patch

Here is a patch that iterates over the previous one but for the entire code base. Overall, I think I like this change for several reasons:
 - Query rewriting is much easier as you don't need to care about boosts (I'm pretty sure the patch fixes some boost handling)
 - Queries don't need to incorporate the boost in their toString() representation
 - it removed the {{queryBoost}} parameter from Similarities and the top level boost and query boost are now applied the same way
 - it removed several APIs: Query.setBoost, Query.getBoost, Query.clone without adding new ones, we just have two additional query implementations: BoostQuery and SpanBoostQuery
 - It allows queries to be fully immutable, ie. we don't need to clone anymore when planning to use a Query as a cache key.

The only downside I see is for the highlighting module: it has to deconstruct queries to understand how they are formed, and this new additional BoostQuery required to add a bit more unwrapping. However, I think the benefits outweight this slight inconvenience.

Any opinions?

> Explore different ways to apply boosts
> --------------------------------------
>
>                 Key: LUCENE-6590
>                 URL: https://issues.apache.org/jira/browse/LUCENE-6590
>             Project: Lucene - Core
>          Issue Type: Wish
>            Reporter: Adrien Grand
>            Priority: Minor
>         Attachments: LUCENE-6590.patch, LUCENE-6590.patch, LUCENE-6690.patch
>
>
> Follow-up from LUCENE-6570: the fact that all queries are mutable in order to allow for applying a boost raises issues since it makes queries bad cache keys since their hashcode can change anytime. We could just document that queries should never be modified after they have gone through IndexSearcher but it would be even better if the API made queries impossible to mutate at all.
> I think there are two main options:
>  - either replace "void setBoost(boost)" with something like "Query withBoost(boost)" which would return a clone that has a different boost
>  - or move boost handling outside of Query, for instance we could have a (immutable) query impl that would be dedicated to applying boosts, that queries that need to change boosts at rewrite time (such as BooleanQuery) would use as a wrapper.
> The latter idea is from Robert and I like it a lot given how often I either introduced or found a bug which was due to the boost parameter being ignored. Maybe there are other options, but I think this is worth exploring.



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