[JOHNZON-293] Potential high memory consumption in DateConverter

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Component/s: Mapper
• Assignee: Unassigned
• Reporter: Alexander Falb
• Created: 03/Dec/19 13:43
• Updated: 25/Apr/22 07:29
• Resolved: 25/Apr/22 07:29

Description

DateConverter 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:

1. Create a new SimpleDateFormat within the toString and fromString methods as method variable instead of a class field.
2. 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):

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

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.

Issue Links

• links to: GitHub Pull Request #55