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https://issues.apache.org/jira/browse/LUCENE-4372?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13452077#comment-13452077
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Yonik Seeley commented on LUCENE-4372:
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bq. btw: what confuses me is what happens in the "run-out-of-ram" case, why do
we even bother collecting the overflow'd docs here (other.collect)?
This was created for grouping. Originally, I always ran the query twice - once
to get the top groups, then again to get the top docs per group. Caching
scores was an optimization added later, but you definitely need to still call
the delegate, even if you run out of cache space.
> CachingCollector.create(boolean, boolean, double) is trappy
> -----------------------------------------------------------
>
> Key: LUCENE-4372
> URL: https://issues.apache.org/jira/browse/LUCENE-4372
> Project: Lucene - Core
> Issue Type: Task
> Reporter: Robert Muir
>
> Followup to LUCENE-3102.
> Shai proposed a method that just caches all scores so they can be replayed:
> {quote}
> Do you think we can modify this Collector to not necessarily wrap another
> Collector? We have such Collector which stores (in-memory) all matching doc
> IDs + scores (if required). Those are later fed into several processes that
> operate on them (e.g. fetch more info from the index etc.). I am thinking, we
> can make CachingCollector optionally wrap another Collector and then someone
> can reuse it by setting RAM limit to unlimited (we should have a constant for
> that) in order to simply collect all matching docs + scores.
> {quote}
> But Mike had concerns about the RAM usage:
> {quote}
> I'd actually rather not have the constant – ie, I don't want to make
> it easy to be unlimited? It seems too dangerous... I'd rather your
> code has to spell out 10*1024 so you realize you're saying 10 GB (for
> example).
> {quote}
> My concern here is what happens when you dont specify enough, I think those
> hits are just silently dropped (which is worse than using lots of RAM).
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