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https://issues.apache.org/jira/browse/LUCENE-3653?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13172274#comment-13172274
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Uwe Schindler edited comment on LUCENE-3653 at 12/19/11 1:50 PM:
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bq. For example it's crazy to use this class [ConcurrentHashMap] to back the
core/reader closed listeners
This is indeed totally crazy, as this is the wrong use-case for this map. This
map should be used when you have lot's of reads and less writes to the map. For
this case, you have only one thread reading (on close only, LOL), but maybe
mayn adding listeners. So this is in general a bug to use CHM here. Should be a
simple sycnrhonized HashMap (which performs better on writes, as it has less
complexity inside).
=> We should open issue for that!
was (Author: thetaphi):
bq. For example it's crazy to use this class to back the core/reader closed
listeners
This is indeed totally crazy, as this is the wrong use-case for this map. This
map should be used when you have lot's of reads and less writes to the map. For
this case, you have only one thread reading (on close only, LOL), but maybe
mayn adding listeners. So this is in general a bug to use CHM here. Should be a
simple sycnrhonized HashMap (which performs better on writes, as it has less
complexity inside).
> 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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