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https://issues.apache.org/jira/browse/FLINK-25728?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17481909#comment-17481909
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Piotr Nowojski commented on FLINK-25728:
----------------------------------------
Thanks for reporting and analysing the issue [~wpc009]. Could you maybe
rephrase why
{code:java}
inputProcessors[i]
.getAvailableFuture()
.thenRun(() -> anyInputAvailable.complete(null))
{code}
is causing this memory leak?
Or maybe let me rephrase it. Let's assume we have two inputs, one is flipping
between available/unavailable status, the other is continuously unavailable.
Now per each {{StreamMultipleInputProcessor#getAvailableFuture}} call, we will
create one {{CompletableFuture<?> anyInputAvailable}}, referenced by TWO
instances {{CompletableFuture$UniRun}}, for
{{inputProcessors[i].getAvailableFuture()}} from each of the inputs.
{{anyInputAvailable}} will be returned, and it will be completed by first input
sooner or later, waking up {{SteamTask}} in the process. That's fine. Now the
problem is that each of those {{anyInputAvailable}} instance will be in this
scenario referenced forever by the second input's
{{inputProcessors[i].getAvailableFuture()}}. As long as the second input is not
available, we are keep building up the memory leak.
Did I understand the problem correctly?
> Potential memory leaks in StreamMultipleInputProcessor
> ------------------------------------------------------
>
> Key: FLINK-25728
> URL: https://issues.apache.org/jira/browse/FLINK-25728
> Project: Flink
> Issue Type: Bug
> Components: Runtime / Task
> Affects Versions: 1.12.5, 1.15.0, 1.13.5, 1.14.2
> Reporter: pc wang
> Priority: Critical
> Labels: pull-request-available
> Attachments: flink-completablefuture-issue.tar.xz,
> image-2022-01-20-18-43-32-816.png
>
>
> We have an application that contains a broadcast process stage. The
> none-broadcast input has roughly 10 million messages per second, and the
> broadcast side is some kind of control stream, rarely has message follow
> through.
> After several hours of running, the TaskManager will run out of heap memory
> and restart. We reviewed the application code without finding any relevant
> issues.
> We found that the running to crash time was roughly the same. Then we make a
> heap dump before the crash and found mass `CompletableFuture$UniRun`
> instances.
> These `CompletableFuture$UniRun` instances consume several gigabytes memories.
>
> The following pic is from the heap dump we get from a mock testing stream
> with the same scenario.
> !image-2022-01-20-18-43-32-816.png|width=1161,height=471!
>
> After some source code research. We found that it might be caused by the
> *StreamMultipleInputProcessor.getAvailableFuture()*.
> *StreamMultipleInputProcessor* has multiple *inputProcessors* , it's
> *availableFuture* got completed when any of it's input's *availableFuture* is
> complete.
> The current implementation create a new *CompletableFuture* and a new
> *CompletableFuture$UniRun* append to delegate inputProcessor's
> *avaiableFuture*.
> The issue is caused by the stacking of *CompletableFuture$UniRun* on the slow
> inputProcessor's *avaiableFuture*.
> See the source code below.
> [StreamMultipleInputProcessor.java#L65|https://github.com/wpc009/flink/blob/d33c39d974f08a5ac520f220219ecb0796c9448c/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/io/StreamMultipleInputProcessor.java#L65]
> Because the *UniRun* holds the reference of outside
> *StreamMultipleInputProcessor*'s avaiableFuture, that cause mass
> *CompletableFuture* instance which can not be recycled.
> We made some modifications to the
> *StreamMultipleInputProcessor*.*getAvaiableFuture* function, and verify that
> the issue is gone on our modified version.
> We are willing to make a PR for this fix.
> Heap Dump File [^flink-completablefuture-issue.tar.xz]
> PS: This is a YourKit heap dump. may be not compatible HPROF files.
> [Sample Code to reproduce the
> issue|https://github.com/wpc009/flink/blob/FLINK-25728/flink-end-to-end-tests/flink-datastream-allround-test/src/main/java/org/apache/flink/streaming/tests/MultipleInputStreamMemoryIssueTest.java]
>
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