ASF GitHub Bot commented on ARTEMIS-1996:

Github user franz1981 commented on the issue:

    @michaelandrepearce good point! I will need to modify it because my 
solution do not create any ByteBuffer at all (or will dispose it immediately 
with Asyncio) and the test proposed won't work as it is

> MappedSequentialFileFactory may cause DirectByteBuffer memory leaks
> -------------------------------------------------------------------
>                 Key: ARTEMIS-1996
>                 URL: https://issues.apache.org/jira/browse/ARTEMIS-1996
>             Project: ActiveMQ Artemis
>          Issue Type: Bug
>          Components: Broker
>            Reporter: tang pu
>            Priority: Minor
> Because of some customization requirements, the readJournalFile method of 
> JournalImpl needs to be calledmultiple times. 
> During the stress test, it was found that almost every 5 hours, the Broker 
> appeared a Full GC.
> This is the information about the Full GC in the GC log.
> {color:#FF0000}2018-07-25T12:14:07.323+0800: 10089.523: [Full GC 
> (System.gc()) 6767M->253M(16G), 8.7138691 secs]{color}
> {color:#FF0000} [Eden: 632.0M(712.0M)->0.0B(816.0M) Survivors: 104.0M->0.0B 
> Heap: 6767.6M(16.0G)->253.9M(16.0G)], [Metaspace: 
> 36323K->35961K(1083392K)]{color}
> {color:#FF0000} [Times: user=2.56 sys=0.42, real=8.71 secs] {color}
> When the Full GC appears, the thread stack is as follows:
> {color:#FF0000}java.lang.System.gc(System.java:993){color}
> {color:#FF0000}java.nio.Bits.reserveMemory(Bits.java:666){color}
> {color:#FF0000}java.nio.DirectByteBuffer.<init>(DirectByteBuffer.java:123){color}
> {color:#FF0000}java.nio.ByteBuffer.allocateDirect(ByteBuffer.java:311){color}
> {color:#FF0000}org.apache.activemq.artemis.core.io.mapped.MappedSequentialFileFactory.newBuffer(MappedSequentialFileFactory.java:109){color}
> {color:#FF0000}org.apache.activemq.artemis.core.journal.impl.JournalImpl.readJournalFile(JournalImpl.java:463){color}
> By analyzing the stack, it should be that the JVM's heap memory cannot be 
> allocated, causing the JVM to call the System.gc() method.
> In the Broker, MappedSequentialFileFactory caches off-heap memory through 
> ThreadLocal. Once the thread is evicted by the CompactExecutor(keepalive is 
> 60s) in the Journal, the heap memory is "leaked".
> {color:#FF0000}NIOSequentialFileFactory{color} also has the same problem

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