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https://issues.apache.org/jira/browse/LUCENE-3102?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Shai Erera updated LUCENE-3102:
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Attachment: LUCENE-3102.patch
Patch includes the bug fixes + test. Still none of the items I listed after
'Also ...'. I plan to tackle that next, in subsequent patches.
Question -- perhaps we can commit these changes incrementally? I.e., after we
iterate on the changes in this patch, if they are ok, commit them, then do the
rest of the stuff? Or a single commit w/ everything is preferable?
Mike, there is another reason to separate Collector.needsScores() from
cacheScores -- it is possible someone will pass a Collector which needs scores,
however won't want to have CachingCollector 'cache' them. In which case, the
wrapped Collector should be delegated setScorer instead of cachedScorer.
I will leave Collector.needsScores() for a different issue though?
> Few issues with CachingCollector
> --------------------------------
>
> Key: LUCENE-3102
> URL: https://issues.apache.org/jira/browse/LUCENE-3102
> Project: Lucene - Java
> Issue Type: Bug
> Components: contrib/*
> Reporter: Shai Erera
> Priority: Minor
> Fix For: 3.2, 4.0
>
> Attachments: LUCENE-3102.patch
>
>
> CachingCollector (introduced in LUCENE-1421) has few issues:
> # Since the wrapped Collector may support out-of-order collection, the
> document IDs cached may be out-of-order (depends on the Query) and thus
> replay(Collector) will forward document IDs out-of-order to a Collector that
> may not support it.
> # It does not clear cachedScores + cachedSegs upon exceeding RAM limits
> # I think that instead of comparing curScores to null, in order to determine
> if scores are requested, we should have a specific boolean - for clarity
> # This check "if (base + nextLength > maxDocsToCache)" (line 168) can be
> relaxed? E.g., what if nextLength is, say, 512K, and I cannot satisfy the
> maxDocsToCache constraint, but if it was 10K I would? Wouldn't we still want
> to try and cache them?
> Also:
> * The TODO in line 64 (having Collector specify needsScores()) -- why do we
> need that if CachingCollector ctor already takes a boolean "cacheScores"? I
> think it's better defined explicitly than implicitly?
> * Let's introduce a factory method for creating a specialized version if
> scoring is requested / not (i.e., impl the TODO in line 189)
> * I think it's a useful collector, which stands on its own and not specific
> to grouping. Can we move it to core?
> * How about using OpenBitSet instead of int[] for doc IDs?
> ** If the number of hits is big, we'd gain some RAM back, and be able to
> cache more entries
> ** NOTE: OpenBitSet can only be used for in-order collection only. So we can
> use that if the wrapped Collector does not support out-of-order
> * 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.
> * I think a set of dedicated unit tests for this class alone would be good.
> That's it so far. Perhaps, if we do all of the above, more things will pop up.
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