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Date: Sat, 17 Dec 2011 22:11:30 +0000 (UTC)
From: "Simon Willnauer (Commented) (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
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Subject: [jira] [Commented] (LUCENE-3653) Lucene Search not scalling
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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 ] 

Simon Willnauer commented on LUCENE-3653:
-----------------------------------------

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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