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From "Uwe Schindler (Commented) (JIRA)" <>
Subject [jira] [Commented] (LUCENE-3653) Lucene Search not scalling
Date Sun, 18 Dec 2011 02:05:30 GMT


Uwe Schindler commented on LUCENE-3653:

bq. Creating a Single -Tokenizer-Analyzer does help, but the thread blocking still happens
because of the synchronization used in several classes.

Not reusing is stupid because of heavy

bq. I agree, if anybody has to decide between, concurrency or storing things twice then concurrency
wins, eventually all the cache data will be available to all threads, and the overhead goes
away. But with synchronization the overhead never goes away.

There are places where we cannot remove synchronization - and those places are no issue at
all. Just because there is synchronization, there is not necessarily a bottleneck. Not everything
you mention is an issue.

bq. RAMFile : all methods are synchronized.

There is contention, but will not slowdown your search. Please keep synchronization there.
every RAMFile is only opened once and then contention is gone. Not everything what your profiler
shows as contention is one, only the first query will have some minor contention.

bq. RAMInputStream: clone() This method came up during the profiling allot. I changed it from
calling clone to: just create an new instance directly.

Thats fine, but same applies here. You only have contention on first few queries.

bq. I'll try to cleanup some of the code and add a better diff.

The VirtualMethod and AttributeSource is already fixed in my patch.

On the time-line of your profiler output I see no improvement in speed. How much faster does
your code get?
> 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-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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