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https://issues.apache.org/jira/browse/FLINK-18353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17142239#comment-17142239
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Andrey Zagrebin commented on FLINK-18353:
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[~stevenz3wu] btw, I do not think that the direct memory can overlap with the
JVM heap because Flink sets the heap min and max value to the same size. This
means that the JVM will probably always reserve the full heap size from OS.
Therefore, the heap cannot be used for the direct memory but the job can
potentially pull the direct memory from the [JVM Metaspace or Overhead memory
components|https://ci.apache.org/projects/flink/flink-docs-master/ops/memory/mem_setup.html#configure-total-memory].
> [1.11.0] maybe document jobmanager behavior change regarding
> -XX:MaxDirectMemorySize
> ------------------------------------------------------------------------------------
>
> Key: FLINK-18353
> URL: https://issues.apache.org/jira/browse/FLINK-18353
> Project: Flink
> Issue Type: Improvement
> Components: Documentation, Runtime / Configuration
> Affects Versions: 1.11.0
> Reporter: Steven Zhen Wu
> Assignee: Andrey Zagrebin
> Priority: Major
>
> I know FLIP-116 (Unified Memory Configuration for Job Managers) is introduced
> in 1.11. That does cause a small behavior change regarding
> `-XX:MaxDirectMemorySize`. Previously, jobmanager don't set JVM arg
> `-XX:MaxDirectMemorySize`, which means JVM can use up to -`Xmx` size for
> direct memory. Now `-XX:MaxDirectMemorySize` is always set to
> [jobmanager.memory.off-heap.size|https://ci.apache.org/projects/flink/flink-docs-master/ops/config.html#jobmanager-memory-off-heap-size]
> config (default 128 mb).
>
> {{It is possible for jobmanager to get "java.lang.OufOfMemoryError: Direct
> Buffer Memory" without tuning
> }}{{[jobmanager.memory.off-heap.size|https://ci.apache.org/projects/flink/flink-docs-master/ops/config.html#jobmanager-memory-off-heap-size]}}
> especially for high-parallelism jobs. Previously, no tuning needed.
>
> Maybe we should point out the behavior change in the migration guide?
> [https://ci.apache.org/projects/flink/flink-docs-master/ops/memory/mem_migration.html#migrate-job-manager-memory-configuration]
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