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https://issues.apache.org/jira/browse/LUCENE-7882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16599031#comment-16599031
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Michael McCandless commented on LUCENE-7882:
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But even once the JVM fixes its bugs and we can safely re-compile all
expressions per query, it should still be faster to avoid that recompilation
when you can?
I think also the lack of {{Accountable}} on a compiled expression makes caching
dangerous – we would have no good way to measure how much RAM is consumed by it.
> 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
> Priority: Major
>
> 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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