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https://issues.apache.org/jira/browse/FLINK-18353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17139541#comment-17139541
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Steven Zhen Wu commented on FLINK-18353:
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[~sewen] that is a good question. It is a tough choice for me.
We haven't seen issue with -XX:MaxDirectMemorySize not set in jobmanager. For
that reason, it is nice to keep it backward compatible.
On the other hand, I can see the value of introducing this for keeping
jobmanager memory config consistent as taskmanager. I am not against this
change. But we plan to increase the default value for
[jobmanager.memory.off-heap.size|https://ci.apache.org/projects/flink/flink-docs-master/ops/config.html#jobmanager-memory-off-heap-size]
to 1 GB in our env.
Does jobmanager mainly use direct memory for the akka control messages to
taskmanagers? I guess in the future world of post FLIP-27 jobmanager may also
run KafkaConsumers for fetching partitions, which may also use some small
amount of direct 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
> 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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