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https://issues.apache.org/jira/browse/LUCENE-7882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16057319#comment-16057319
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Dawid Weiss commented on LUCENE-7882:
-------------------------------------
These one-off class loaders should be gc-ed if there are no root refs pointing
at anything they declared. This should be relatively easy to verify if you dump
the heap incrementally over time (yourkit is your friend here).
The blocked thread is possibly a related issue (if they do have some
synchronization going on internally), but I don't see where that could occur.
Try the things Robert mentioned. Interesting stuff.
> Maybe expression compiler should cache recently compiled expressions?
> ---------------------------------------------------------------------
>
> Key: LUCENE-7882
> URL: https://issues.apache.org/jira/browse/LUCENE-7882
> Project: Lucene - Core
> Issue Type: Improvement
> Components: modules/expressions
> Reporter: Michael McCandless
>
> I've been running search performance tests using a simple expression
> ({{_score + ln(1000+unit_sales)}}) for sorting and hit this odd bottleneck:
> {noformat}
> "pool-1-thread-30" #70 prio=5 os_prio=0 tid=0x00007eea7000a000 nid=0x1ea8a
> waiting for monitor entry [0x00007eea867dd000]
> java.lang.Thread.State: BLOCKED (on object monitor)
> at
> org.apache.lucene.expressions.js.JavascriptCompiler$CompiledExpression.evaluate(_score
> + ln(1000+unit_sales))
> at
> org.apache.lucene.expressions.ExpressionFunctionValues.doubleValue(ExpressionFunctionValues.java:49)
> at
> com.amazon.lucene.OrderedVELeafCollector.collectInternal(OrderedVELeafCollector.java:123)
> at
> com.amazon.lucene.OrderedVELeafCollector.collect(OrderedVELeafCollector.java:108)
> at
> org.apache.lucene.search.MultiCollectorManager$Collectors$LeafCollectors.collect(MultiCollectorManager.java:102)
> at
> org.apache.lucene.search.Weight$DefaultBulkScorer.scoreAll(Weight.java:241)
> at
> org.apache.lucene.search.Weight$DefaultBulkScorer.score(Weight.java:184)
> at org.apache.lucene.search.BulkScorer.score(BulkScorer.java:39)
> at org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:658)
> at org.apache.lucene.search.IndexSearcher$5.call(IndexSearcher.java:600)
> at org.apache.lucene.search.IndexSearcher$5.call(IndexSearcher.java:597)
> at java.util.concurrent.FutureTask.run(FutureTask.java:266)
> at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> at java.lang.Thread.run(Thread.java:745)
> {noformat}
> I couldn't see any {{synchronized}} in the sources here, so I'm not sure
> which object monitor it's blocked on.
> I was accidentally compiling a new expression for every query, and that
> bottleneck would cause overall QPS to slow down drastically (~4X slower after
> ~1 hour of redline tests), as if the JVM is getting slower and slower to
> evaluate each expression the more expressions I had compiled.
> I tested JDK 9-ea and it also kept slowing down over time as the performance
> test ran.
> Maybe we should put a small cache in front of the expressions compiler to
> make it less trappy? Or maybe we can get to the root cause of why the JVM
> slows down more and more, the more expressions you compile?
> I won't have time to work on this in the near future so if anyone else feels
> the itch, please scratch it!
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