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From "Simon Willnauer (Updated) (JIRA)" <>
Subject [jira] [Updated] (LUCENE-3653) Lucene Search not scalling
Date Mon, 19 Dec 2011 09:00:31 GMT


Simon Willnauer updated LUCENE-3653:

    Attachment: LUCENE-3653.patch

here is a patch that removes the sync on SegmentCoreReaders#getTermsReader() - since this
method is access on basically every search we should try to prevent any sync even if they
are cheap in the uncontended case.
> Lucene Search not scalling
> --------------------------
>                 Key: LUCENE-3653
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>            Reporter: Gerrit Jansen van Vuuren
>         Attachments:, LUCENE-3653-VirtualMethod+AttributeSource.patch, LUCENE-3653-VirtualMethod+AttributeSource.patch,
LUCENE-3653-VirtualMethod+AttributeSource.patch, LUCENE-3653.patch, 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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