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https://issues.apache.org/jira/browse/LUCENE-1483?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12664979#action_12664979
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Michael McCandless commented on LUCENE-1483:
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bq. Even still, you are seeing like a 40% diff, but small enough times to not
matter.
Right, good point.
I think the massive slowness of iterating through all terms & docs
from a MultiTermEnum/Docs may come from asking the N-1 SegmentReaders
to seek to a non-existent (for them) term.
Ie when we ask MultiTermDocs to seek to a unique title X, only the
particular segment that title X comes from actually has it, whereas
the others do a costly seek to the index term just before it then scan
to look for the non-existent term, and then repeat that for the next
title, etc.
In fact this probably causes the underlying buffer in
BufferedIndexReader to get reloaded many times whenever we cross a
boundary (ie, we keep flipping between buffer N and N+1, then back to
N then N+1 again, etc.) -- maybe that's the source massive slowness?
BTW I think this change may also speed up Range/PrefixQuery as well.
> Change IndexSearcher multisegment searches to search each individual segment
> using a single HitCollector
> --------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-1483
> URL: https://issues.apache.org/jira/browse/LUCENE-1483
> Project: Lucene - Java
> Issue Type: Improvement
> Affects Versions: 2.9
> Reporter: Mark Miller
> Priority: Minor
> Attachments: LUCENE-1483-partial.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> sortBench.py, sortCollate.py
>
>
> FieldCache and Filters are forced down to a single segment reader, allowing
> for individual segment reloading on reopen.
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