[LUCENE-7882] Maybe expression compiler should cache recently compiled expressions?

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: modules/expressions
• Lucene Fields: New
• Assignee: Uwe Schindler
• Reporter: Michael McCandless
• Created: 19/Jun/17 13:12
• Updated: 28/Aug/22 15:16

Description

I've been running search performance tests using a simple expression (_score + ln(1000+unit_sales)) for sorting and hit this odd bottleneck:

"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)

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!

Issue Links

• links to: GitHub Pull Request #1837