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https://issues.apache.org/jira/browse/LUCENE-3653?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13172348#comment-13172348
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Uwe Schindler commented on LUCENE-3653:
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bq. Oh, ok I thought RAMDirectory would make things faster, good to know. I
will try with MMapDirectory then post back.
Thats a hard to eliminate misbelief - same like "optimizing indexes is good".
Just remember that MMapDirectory will use memory outside the JVM heap. If the
whole index is in file system cache, Lucene can directly access the cache using
MMapDirectory (thats like a swap file, loaded on demand). So reduce JVM heap
and supply lots of space for the OS kernel to cache file contents, as those are
mapped by MMAP into Java's process space.
> 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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