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https://issues.apache.org/jira/browse/LOG4J2-1125?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14936005#comment-14936005
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Remko Popma commented on LOG4J2-1125:
-------------------------------------
Testing that hypothesis is what drove this Jira ticket. The "Before" benchmark
in the description creates a new StringBuilder(1024) for each log event. The
benchmark shows a significant performance improvement by reusing the
StringBuilder instance in a ThreadLocal.
[~dmitri_blinov]: If you read the output you posted from Catalina.out
carefully, you will see that Tomcat is merely telling us that it noticed the
ThreadLocal, and that it will deal with it by renewing the thread pool to
prevent a memory leak.
Since Tomcat 7.0.6, ThreadLocals no longer cause a memory leak. See also
http://wiki.apache.org/tomcat/MemoryLeakProtection
> 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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