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From Paul Smith <>
Subject Sorting, RuleBasedCollater, and synchronization bottleneck
Date Wed, 14 Feb 2007 08:03:07 GMT
Hi ho peoples.

We have an application that is internationalized, and stores data  
from many languages (each project has it's own index, mostly aligned  
with a single language, maybe 2).

Anyway, I've noticed during some thread dumps diagnosing some  
performance issues, that there appears to be a _potential_  
synchronization bottleneck using Locale-based sorting of Strings.  I  
don't think this problem is the root cause of our performance  
problem, but I thought I'd mention it here.  Here's the stack dump of  
a thread waiting:

"http-1001-Processor245" daemon prio=1 tid=0x31434da0 nid=0x3744  
waiting for monitor entry [0x2cd44000..0x2cd45f30]
         - waiting to lock <0x6b1e8c68> (a java.text.RuleBasedCollator)
         at org.apache.lucene.util.PriorityQueue.upHeap 
         at org.apache.lucene.util.PriorityQueue.put 
         at org.apache.lucene.util.PriorityQueue.insert 

In our case we had 12 threads waiting like this, while one thread had  
the lock on the RuleBasedCollator.  Turns out  
RuleBasedCollator' method is synchronized.  I wonder if  
a ThreadLocal based collator would be better here... ?  There doesn't  
appear to be a reason for other threads searching the same index to  
wait on this sort.  Be just as easy to use their own.  (Is  
RuleBasedCollator a "heavy" object memory wise?  Wouldn't have  
thought so, per thread)


Paul Smith
Engineering Manager

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