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https://issues.apache.org/jira/browse/LUCENE-7577?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15708807#comment-15708807
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Robert Muir commented on LUCENE-7577:
-------------------------------------

Well, I'm not that strongly opinionated on it to block the change, I just think 
its important to look at the tradeoffs. This class is a part of indexwriter, 
and indexwriter is complicated. 

I don't think its good to let some esoteric queries make the index package even 
more complicated than it needs to be.

I already don't like that termsquery & co use it from the beginning, i mean 
that change is really unfortunate since it means prefixcodedterms and ramfile 
both have to have hashcode/equals at all: just to support these queries!

adding stuff like caching the hashcode, i mean its not that i'm against that 
one little change, esp since its immutable, but its just continuing in the same 
direction. 

Its also the case that lucene queries have historically had a ton of hashcode 
and equals bugs, and adding optimizations for that, man, I honestly think that 
isn't a good idea and shouldnt be done at all, anywhere. Lucene isn't tall 
enough to ride, it shouldn't have optimizations like this unless something is 
changed to show it can have correctness first. but adding those optos to a 
piece that indexwriter uses for low level stuff? IMO that's even more 
dangerous, especially around equals/hashcode which could easily "slip in" to IW 
without much notice due to how it works in java.


> PrefixCodedTerms should cache its hash code
> -------------------------------------------
>
>                 Key: LUCENE-7577
>                 URL: https://issues.apache.org/jira/browse/LUCENE-7577
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Adrien Grand
>            Assignee: Adrien Grand
>            Priority: Minor
>         Attachments: LUCENE-7577.patch
>
>
> We have several queries that cache the hashcode of a PrefixCodedTerms 
> instance on top of it, so we could simplify by moving the caching to 
> PrefixCodedTerms directly.



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