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From "Aniket Bhatnagar (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (SPARK-18787) spark.shuffle.io.preferDirectBufs does not completely turn off direct buffer usage by Netty
Date Fri, 09 Dec 2016 08:50:59 GMT

     [ https://issues.apache.org/jira/browse/SPARK-18787?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Aniket Bhatnagar updated SPARK-18787:
-------------------------------------
    Description: 
The documentation for the configuration spark.shuffle.io.preferDirectBufs states that it will
force all allocations from Netty to be on-heap but this currently does not happen. The reason
is that preferDirect of Netty's PooledByteBufAllocator doesn't completely eliminate use of
off heap by Netty. In order to completely stop netty from using off heap memory, we need to
set the following system properties:
- io.netty.noUnsafe=true
- io.netty.threadLocalDirectBufferSize=0

The proposal is to set properties (using System.setProperties) when the executor starts (before
any of the Netty classes load) or document these properties to hint users on how to completely
eliminate Netty' off heap footprint.

  was:
The documentation for the configuration spark.shuffle.io.preferDirectBufs states that it will
force all allocations from Netty to be on-heap but this currently does not happen. The reason
is that preferDirect of Netty's PooledByteBufAllocator doesn't completely eliminate use of
off heap by Netty. In order to completely stop netty from using off heap memory, we need to
set the following system properties:
- io.netty.noUnsafe=true
- io.netty.threadLocalDirectBufferSize=0

The proposal is to set properties (using System.setProperties) when the executor starts (before
any of the Netty classes load) or document these properties to hint users on how to completely
eliminate off Netty' heap footprint.


> spark.shuffle.io.preferDirectBufs does not completely turn off direct buffer usage by
Netty
> -------------------------------------------------------------------------------------------
>
>                 Key: SPARK-18787
>                 URL: https://issues.apache.org/jira/browse/SPARK-18787
>             Project: Spark
>          Issue Type: Bug
>    Affects Versions: 2.0.2
>            Reporter: Aniket Bhatnagar
>
> The documentation for the configuration spark.shuffle.io.preferDirectBufs states that
it will force all allocations from Netty to be on-heap but this currently does not happen.
The reason is that preferDirect of Netty's PooledByteBufAllocator doesn't completely eliminate
use of off heap by Netty. In order to completely stop netty from using off heap memory, we
need to set the following system properties:
> - io.netty.noUnsafe=true
> - io.netty.threadLocalDirectBufferSize=0
> The proposal is to set properties (using System.setProperties) when the executor starts
(before any of the Netty classes load) or document these properties to hint users on how to
completely eliminate Netty' off heap footprint.



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