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https://issues.apache.org/jira/browse/LUCENE-3653?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13171691#comment-13171691
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Simon Willnauer commented on LUCENE-3653:
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bq. The SegmentCoreReaders sync cannot be removed in Lucene 3.x, as segments
are read/write. You can remove the synchronization partly in your Lucene
instance by patching it, the risk is on your side! This is not a bug in Lucene.
In Lucene trunk, most of this sync is removed as IndexReaders will be pure
read-only. We are currently working on removing contention in SegmentReader's
SegmentCore.
Uwe, I had a quick look at it and I think we can remove this. We set the tis in
the ctor or if we load a NRT reader. So basically we can assign the tisNoIndex
reader to the tis instead of leaving it will a null ref and use a second
boolean to actually signal if it was loaded or not. for read access this is not
necessarily required to be synced since if you pull a NRT reader you can rely
on the IW sync / mem barrier to see the latest reference. I will take a closer
look at this next week.
> 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, 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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