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https://issues.apache.org/jira/browse/JOHNZON-293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17271615#comment-17271615
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Mark Struberg commented on JOHNZON-293:
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[~elexx] did you find some time to dig into this? txs!
> Potential high memory consumption in DateConverter
> --------------------------------------------------
>
> Key: JOHNZON-293
> URL: https://issues.apache.org/jira/browse/JOHNZON-293
> Project: Johnzon
> Issue Type: Bug
> Components: Mapper
> Reporter: Alexander Falb
> Priority: Major
> Time Spent: 40m
> Remaining Estimate: 0h
>
> [DateConverter|https://github.com/apache/johnzon/blob/master/johnzon-mapper/src/main/java/org/apache/johnzon/mapper/converter/DateConverter.java]
> creates a new SimpleDateFormat for every instance for every thread the
> instance is used on and never cleans them up. This may cause a high memory
> usage, if lots of those converters are created instead of reused.
>
> Two approaches to get rid of them are on my mind:
> # Create a new SimpleDateFormat within the toString and fromString methods
> as method variable instead of a class field.
> # Use java.time.DateTimeFormatter as class field, because it is immutable
> and thread-safe, and do some object conversion from java.util.Date to/from
> java.time.ZonedDateTime.
>
> I did some JMH performance tests for both (full project can be found here
> [https://github.com/elexx/dateconverter-benchmark]):
> {noformat}
> Benchmark Mode Cnt Score
> Error Units
> JavaTimeDateFormatterBenchmark.formatNewFormat avgt 5 828,623 ±
> 8,836 ns/op
> JavaTimeDateFormatterBenchmark.formatReuseFormat avgt 5 496,916 ±
> 5,150 ns/op
> JavaTimeDateFormatterBenchmark.parseNewFormat avgt 5 1430,276 ±
> 11,084 ns/op
> JavaTimeDateFormatterBenchmark.parseReuseFormat avgt 5 990,648 ±
> 280,983 ns/op
> SimpleDateFormatterBenchmark.formatNewFormat avgt 5 1308,144 ±
> 13,993 ns/op
> SimpleDateFormatterBenchmark.formatReuseFormat avgt 5 392,236 ±
> 3,219 ns/op
> SimpleDateFormatterBenchmark.parseNewFormat avgt 5 1848,772 ±
> 19,412 ns/op
> SimpleDateFormatterBenchmark.parseReuseFormat avgt 5 1121,955 ±
> 12,417 ns/op
> {noformat}
> In this quick test it looks like creating a new SimpleDateFormatter in each
> method is quite slow (1308ns/op + 1848ns/op).
> Reusing the SimpleDateFormatter is faster (392ns/op + 1121ns/op), but no
> option because it is not thread-safe.
> Reusing the Java8-DateTimeFormatter is equivalent (496ns/op + 990ns/op) to
> Reusing SimpleDateFormatter (parsing is faster, formatting is slower, avg is
> about the same)
> And just for completeness: Creating a Java8-DateTimeFormatter, which is
> nonsense, because it is immutable and thread-safe.
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