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From "Yonik Seeley (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4372) CachingCollector.create(boolean, boolean, double) is trappy
Date Mon, 10 Sep 2012 15:32:07 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4372?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13452077#comment-13452077
] 

Yonik Seeley commented on LUCENE-4372:
--------------------------------------

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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