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https://issues.apache.org/jira/browse/LUCENE-7882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17197237#comment-17197237
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Haoyu Zhai commented on LUCENE-7882:
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Hi Uwe
Thank you for making this fantastic PR!
This issue was a bug in our service that would incorrectly recompile many
expressions and it is fixed, now we only see ~500 expression compiled per
benchmark run.
We've tested this PR by compiling with JDK11 and running with JDK15 (because of
some reason it's not easy to compile our service with JDK15 directly). But
because of the reason I mentioned above, it seems that we don't have enough
expressions compilation now to observe the difference with or without the PR.
> 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
> Assignee: Uwe Schindler
> Priority: Major
> Attachments: demo.patch
>
> Time Spent: 1.5h
> Remaining Estimate: 0h
>
> 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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