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https://issues.apache.org/jira/browse/LOG4J2-2269?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16394482#comment-16394482
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Dmitry Konstantinov commented on LOG4J2-2269:
---------------------------------------------
Please find in attach a code to reproduce the problem -
[^test_to_reproduce.zip]. It is not pure Unit test, it is quite tricky to
reproduce the problem in format of a usual unit test because the observable
effects are side ones.
If we run the test with -Dlog4j2.enableThreadlocals=true (default) we got a
result like:
{code}
Used heap size: 101 Mb, max heap size: 245 Mb
{code}
at the end of execution.
For -Dlog4j2.enableThreadlocals=false the same test gives:
{code}
Used heap size: 3 Mb, max heap size: 245 Mb
{code}
Heap dumps for both cases are also attached to the ticket:
[^heap_dump_threadLocals_false.hprof.zip] ,
[^heap_dump_threadLocals_true.hprof.zip]
In heap dump [^heap_dump_threadLocals_true.hprof.zip] we see that the
application level heavy objects (TaskContext) are kept in memory because of
log4j2 references in thread locals:
!heap_dump_references.png!
> Memory leaking of replacement parameters in case of enableThreadlocals=true
> ---------------------------------------------------------------------------
>
> Key: LOG4J2-2269
> URL: https://issues.apache.org/jira/browse/LOG4J2-2269
> Project: Log4j 2
> Issue Type: Bug
> Components: Core
> Reporter: Dmitry Konstantinov
> Assignee: Remko Popma
> Priority: Major
> Attachments: heap_dump_references.png,
> heap_dump_threadLocals_false.hprof.zip,
> heap_dump_threadLocals_true.hprof.zip, test_to_reproduce.zip
>
>
> Use case:
> 1) I have a thread pool with quite large number of threads (around 100)
> 2) Threads from the pool sometimes process some heavy objects. Threads are
> not actively writing into logs (so, a thread may process a task and does not
> log any message).
> 3) As a part of processing for some objects in some non-frequently used
> branch a thread logged a message with heavy replacement parameters
> (parameterized log message is used).
> In this case such heavy replacement parameters are not garbage collected
> until another message will not written within the same thread because
> thread-local ReusableParameterizedMessage and MutableLogEvent objects keep
> references to the replacement parameters.
> Is it possible to cleanup such references when a message is released (for
> example as a part of
> org.apache.logging.log4j.message.ReusableMessageFactory#release and
> org.apache.logging.log4j.core.impl.ReusableLogEventFactory#release) to avoid
> such kind of leaks?
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