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https://issues.apache.org/jira/browse/LUCENE-7963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16158498#comment-16158498
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Uwe Schindler commented on LUCENE-7963:
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I think this was a relict from debugging! This was caused by LUCENE-7626.
About the patch: Patch is fine, thanks also for removing the import! +1
> Write to termAttr causes performance drop
> -----------------------------------------
>
> Key: LUCENE-7963
> URL: https://issues.apache.org/jira/browse/LUCENE-7963
> Project: Lucene - Core
> Issue Type: Bug
> Components: core/index
> Affects Versions: 7.0
> Environment: *Hardware*
> i3.16xlarge (Intel(R) Xeon(R) CPU E5-2686 v4 @ 2.30GHz, 64 cores, two sockets)
> *Software*
> * Ubuntu 16.04 (kernel 4.4.0-1022-aws)
> * Java 1.8.0_144
> Reporter: Daniel Mitterdorfer
> Fix For: 7.0
>
> Attachments: 0001-Remove-unused-variable-in-DefaultIndexingChain.patch
>
>
> Some background: We have spotted a significant drop in indexing throughput on
> machines with a large number of cores (see
> https://github.com/elastic/elasticsearch/issues/26339 for details).
> We finally managed to isolate the behavior in a JMH "microbenchmark". Here is
> the output of running that benchmark with 32 threads with JMH's perfasm
> profiler (also Oracle Development Studio finds the same hotspot):
> {code}
> ....[Hottest Region
> 1]..............................................................................
> C2, level 4, org.apache.lucene.index.DefaultIndexingChain$PerField::invert,
> version 1231 (792 bytes)
> 0x00007f52d56b026a: xor %r10d,%r10d
> ;*invokevirtual isAssignableFrom
> ; -
> org.apache.lucene.util.AttributeSource::addAttribute@28 (line 207)
> ; -
> org.apache.lucene.document.Field$BinaryTokenStream::<init>@8 (line 512)
> ; -
> org.apache.lucene.document.Field::tokenStream@82 (line 491)
> ; -
> org.apache.lucene.index.DefaultIndexingChain$PerField::invert@99 (line 729)
> 0x00007f52d56b026d: mov $0x8,%r11d
> ;*invokeinterface iterator
> ; -
> org.apache.lucene.util.AttributeSource::getCurrentState@46 (line 254)
> ; -
> org.apache.lucene.util.AttributeSource::clearAttributes@1 (line 269)
> ; -
> org.apache.lucene.document.Field$BinaryTokenStream::incrementToken@10 (line
> 532)
> ; -
> org.apache.lucene.index.DefaultIndexingChain$PerField::invert@153 (line 736)
> 0.00% 0.02% ↗ 0x00007f52d56b0273: test %r10,%r10
> ╭ │ 0x00007f52d56b0276: je 0x00007f52d56b0292
> ;*getfield fieldsData
> │ │ ; -
> org.apache.lucene.document.Field::binaryValue@1 (line 441)
> │ │ ; -
> org.apache.lucene.document.Field::tokenStream@65 (line 487)
> │ │ ; -
> org.apache.lucene.index.DefaultIndexingChain$PerField::invert@99 (line 729)
> 0.00% 0.00% │ │ 0x00007f52d56b0278: mov (%r11),%rsi
> ;*getfield next
> │ │ ; -
> java.util.HashMap::getNode@137 (line 580)
> │ │ ; -
> java.util.LinkedHashMap::get@6 (line 440)
> │ │ ; -
> org.apache.lucene.util.AttributeSource::getAttribute@6 (line 245)
> │ │ ; -
> org.apache.lucene.index.DefaultIndexingChain$PerField::invert@143 (line 734)
> 0.09% 0.51% │ │ 0x00007f52d56b027b: mov 0x18(%rsi),%r8
> 23.70% 3.54% │ │ 0x00007f52d56b027f: mov $0x7f4926a81d88,%rcx ;
>
> {metadata('org/apache/lucene/analysis/tokenattributes/CharTermAttribute')}
> 0.00% 0.00% │ │ 0x00007f52d56b0289: cmp %rcx,%r8
> │ │ 0x00007f52d56b028c: jne 0x00007f52d56b0949
> ;*instanceof
> │ │ ; -
> org.apache.lucene.document.Field::binaryValue@4 (line 441)
> │ │ ; -
> org.apache.lucene.document.Field::tokenStream@65 (line 487)
> │ │ ; -
> org.apache.lucene.index.DefaultIndexingChain$PerField::invert@99 (line 729)
> 0.01% 0.00% ↘ │ 0x00007f52d56b0292: test %r10,%r10
> │ 0x00007f52d56b0295: je 0x00007f52d56b1e0d
> ;*invokevirtual addAttributeImpl
> │ ; -
> org.apache.lucene.util.AttributeSource::addAttribute@80 (line 213)
> │ ; -
> org.apache.lucene.document.Field$StringTokenStream::<init>@8 (line 550)
> │ ; -
> org.apache.lucene.document.Field::tokenStream@47 (line 483)
> │ ; -
> org.apache.lucene.index.DefaultIndexingChain$PerField::invert@99 (line 729)
> 0.01% 0.00% │ 0x00007f52d56b029b: mov (%r11),%rsi
> ;*invokevirtual hashCode
> │ ; -
> java.util.HashMap::hash@9 (line 338)
> │ ; -
> java.util.LinkedHashMap::get@2 (line 440)
> │ ; -
> org.apache.lucene.util.AttributeSource::getAttribute@6 (line 245)
> │ ; -
> org.apache.lucene.index.DefaultIndexingChain$PerField::invert@143 (line 734)
> {code}
> You can see that a significant amount of time is spent in {{mov
> $0x7f4926a81d88,%rcx}}. It turns out that this maps to the following line in
> Java ({{DefaultIndexingChain$PerField::invert}}):
> {code:java}
> CharTermAttribute termAtt = tokenStream.getAttribute(CharTermAttribute.class);
> {code}
> Which is - luckily - unused (and removed by the attached patch).
> We have verified the impact of the change with an Elasticsearch
> macrobenchmark which indexes 165,346,692 documents (~ 74GB) with 24 clients
> concurrently. The reported numbers are median indexing throughput during that
> benchmark against a single Elasticsearch node:
> * Without the patch: 125418 documents/s
> * With the patch: 221237 documents/s
> Details about the benchmark setup etc. are mentioned in the [Elasticsearch
> issue #26339|https://github.com/elastic/elasticsearch/issues/26339] if you're
> interested.
> Unfortunately, it is beyond me why writing this register to main memory takes
> such a long time and why C2 did not eliminate this line as dead code to begin
> with.
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