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https://issues.apache.org/jira/browse/SPARK-24938?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16579177#comment-16579177
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Imran Rashid commented on SPARK-24938:
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yeah thats about what I expected. Its worse than 16MB per "service" in some
cases, though -- it'll be 16 MB per netty thread, which will max out at 8.
You'll see that a lot on the driver. So could save 384 MB on the driver, and I
think 128 MB in the external shuffle service (where only one service is active,
I think).
Did you see a corresponding increase in the offheap pools? I expected them to
*not* grow (as spark actually only needs a tiny bit of space from these pools,
so it should be able to find that space in the existing offheap pools).
> Understand usage of netty's onheap memory use, even with offheap pools
> ----------------------------------------------------------------------
>
> Key: SPARK-24938
> URL: https://issues.apache.org/jira/browse/SPARK-24938
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Affects Versions: 2.4.0
> Reporter: Imran Rashid
> Priority: Major
> Labels: memory-analysis
>
> We've observed that netty uses large amount of onheap memory in its pools, in
> addition to the expected offheap memory when I added some instrumentation
> (using SPARK-24918 and https://github.com/squito/spark-memory). We should
> figure out why its using that memory, and whether its really necessary.
> It might be just this one line:
> https://github.com/apache/spark/blob/master/common/network-common/src/main/java/org/apache/spark/network/protocol/MessageEncoder.java#L82
> which means that even with a small burst of messages, each arena will grow by
> 16MB which could lead to a 128 MB spike of an almost entirely unused pool.
> Switching to requesting a buffer from the default pool would probably fix
> this.
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