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https://issues.apache.org/jira/browse/LUCENE-3653?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13172322#comment-13172322
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Gerrit Jansen van Vuuren commented on LUCENE-3653:
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IndexSearch.doc calls RAMFile indirectly through RAMInputStream, once search is
complete you need to know what's been found so IndexSearch.doc needs to be
called.
i.e. RAMInputStream calls RAMFile.numBuffers and getBuffer on the
switchCurrentBuffer which happens allot during my searches.
IndexSearcher calls TermQuery$TermWeightScorer.scorer which calls
SegmentReader.norms, which calls SegmentNorms.bytes on each search.
SegmentNorms has almost all methods synchronized.
> Lucene Search not scalling
> --------------------------
>
> Key: LUCENE-3653
> URL: https://issues.apache.org/jira/browse/LUCENE-3653
> Project: Lucene - Java
> Issue Type: Improvement
> Reporter: Gerrit Jansen van Vuuren
> Attachments: App.java,
> LUCENE-3653-VirtualMethod+AttributeSource.patch,
> LUCENE-3653-VirtualMethod+AttributeSource.patch,
> LUCENE-3653-VirtualMethod+AttributeSource.patch, LUCENE-3653-no-sync.png,
> LUCENE-3653-sync-.png, LUCENE-3653.patch,
> LUCENE-3653.patch-BiasedLockingStartupDelay_1.png,
> LUCENE-3653.patch-BiasedLockingStartupDelay_2.png,
> LUCENE-3653.patch-BiasedLockingStartupDelay_3.png,
> Threads-LUCENE-3653.patch.png, lucene-unsync.diff, profile_1_a.png,
> profile_1_b.png, profile_1_c.png, profile_1_d.png, profile_2_a.png,
> profile_2_b.png, profile_2_c.png
>
>
> I've noticed that when doing thousands of searches in a single thread the
> average time is quite low i.e. a few milliseconds. When adding more
> concurrent searches doing exactly the same search the average time increases
> drastically.
> I've profiled the search classes and found that the whole of lucene blocks on
> org.apache.lucene.index.SegmentCoreReaders.getTermsReader
> org.apache.lucene.util.VirtualMethod
> public synchronized int getImplementationDistance
> org.apache.lucene.util.AttributeSourcew.getAttributeInterfaces
> These cause search times to increase from a few milliseconds to up to 2
> seconds when doing 500 concurrent searches on the same in memory index. Note:
> That the index is not being updates at all, so not refresh methods are called
> at any stage.
> Some questions:
> Why do we need synchronization here?
> There must be a non-lockable solution for these, they basically cause
> lucene to be ok for single thread applications but disastrous for any
> concurrent implementation.
> I'll do some experiments by removing the synchronization from the methods of
> these classes.
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