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https://issues.apache.org/jira/browse/LOG4J2-1125?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14936386#comment-14936386
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Dmitri Blinov commented on LOG4J2-1125:
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While I agree that tomcat tries to do its best to clean up leaks I believe
"SEVERE" logging level of the message indicates we have troubles, the messages
that are merely telling us something are with "INFO" level. Other containers
like WebSphere may not support cleaning up ThreadLocal-s and not every thread
inside tomcat may be respawned, thus keeping a link to old webapp classloader
and preventing it from being GC-ed.
> Reuse StringBuilder to improve performance for PatternLayout
> ------------------------------------------------------------
>
> Key: LOG4J2-1125
> URL: https://issues.apache.org/jira/browse/LOG4J2-1125
> Project: Log4j 2
> Issue Type: Improvement
> Components: Layouts
> Affects Versions: 2.3
> Reporter: Remko Popma
> Assignee: Remko Popma
> Fix For: 2.4
>
>
> As part of the investigation for LOG4J2-930 (PatternLayout performance), I
> found that in PatternLayout.toSerializable(), instead of creating a new
> StringBuilder each time this method is called, caching and reusing a
> ThreadLocal<StringBuilder> makes a huge difference in performance.
> *Before (new StringBuilder instance for each event)*
> {code}
> Benchmark Mode Samples
> Score Error Units
> o.a.l.l.p.j.PatternLayoutComparisonBenchmark.log4j2 sample 125646
> 1413.362 ± 33.806 ns/op
> o.a.l.l.p.j.PatternLayoutComparisonBenchmark.logback sample 128680
> 1383.201 ± 33.076 ns/op
> {code}
> *After (reuse ThreadLocal<StringBuilder>)*
> {code}
> Benchmark Mode Samples
> Score Error Units
> o.a.l.l.p.j.PatternLayoutComparisonBenchmark.log4j2 sample 156816
> 1138.547 ± 20.290 ns/op
> o.a.l.l.p.j.PatternLayoutComparisonBenchmark.logback sample 127978
> 1355.166 ± 19.462 ns/op
> {code}
> org.apache.logging.log4j.PerformanceComparison results indicate this improves
> overall performance:
> *Before (new StringBuilder instance for each event)*
> {code}
> Log4j : 1501
> Logback : 1208
> Log4j 2.0: 1646
> ###############################################
> Log4j : 1487
> Logback : 1165
> Log4j 2.0: 1566
> ###############################################
> Log4j : 1490
> Logback : 1170
> Log4j 2.0: 1485
> ###############################################
> Log4j : 1392
> Logback : 1143
> Log4j 2.0: 1629
> {code}
> *After (reuse ThreadLocal<StringBuilder>)*
> {code}
> Log4j : 1498
> Logback : 1202
> Log4j 2.0: 1213
> ###############################################
> Log4j : 1394
> Logback : 1057
> Log4j 2.0: 1290
> ###############################################
> Log4j : 1240
> Logback : 1109
> Log4j 2.0: 1335
> ###############################################
> Log4j : 1310
> Logback : 1146
> Log4j 2.0: 1210
> {code}
> There are more changes for LOG4J2-930, so I am splitting off this item into a
> separate ticket so I can address it and close it.
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