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https://issues.apache.org/jira/browse/SPARK-30978?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xingbo Jiang updated SPARK-30978:
---------------------------------
    Description: 
Based on our experience, there is no scenario that necessarily requires 
deploying multiple Workers on the same node with Standalone backend. A worker 
should book all the resources reserved to Spark on the host it is launched, 
then it can allocate those resources to one or more executors launched by this 
worker. Since each executor runs in a separated JVM, we can limit the memory of 
each executor to avoid long GC pause.

The remaining concern is the local-cluster mode is implemented by launching 
multiple workers on the local host, we might need to re-implement 
LocalSparkCluster to launch only one Worker and multiple executors. It should 
be fine because local-cluster mode is only used in running Spark unit test 
cases, thus end users should not be affected by this change.

Removing multiple workers on the same host support could simplify the deploy 
model of Standalone backend, and also reduce the burden to support legacy 
deploy pattern in the future feature developments.

The proposal is to update the document to deprecate the support of system 
environment `SPARK_WORKER_INSTANCES` in 3.0, and remove the support in the next 
major version (3.1.0).

  was:
Based on our experience, there is no scenario that necessarily requires 
deploying multiple Workers on the same node with Standalone backend. A worker 
should book all the resources reserved to Spark on the host it is launched, 
then it can allocate those resources to one or more executors launched by this 
worker. Since each executor runs in a separated JVM, we can limit the memory of 
each executor to avoid long GC pause.

The remaining concern is the local-cluster mode is implemented by launching 
multiple workers on the local host, we might need to re-implement 
LocalSparkCluster to launch only one Worker and multiple executors. It should 
be fine because local-cluster mode is only used in running Spark unit test 
cases, thus end users should not be affected by this change.

Removing multiple workers on the same host support could simplify the deploy 
model of Standalone backend, and also reduce the burden to support legacy 
deploy pattern in the future feature developments.


> Remove multiple workers on the same host support from Standalone backend
> ------------------------------------------------------------------------
>
>                 Key: SPARK-30978
>                 URL: https://issues.apache.org/jira/browse/SPARK-30978
>             Project: Spark
>          Issue Type: Task
>          Components: Spark Core
>    Affects Versions: 3.0.0, 3.1.0
>            Reporter: Xingbo Jiang
>            Assignee: Xingbo Jiang
>            Priority: Major
>
> Based on our experience, there is no scenario that necessarily requires 
> deploying multiple Workers on the same node with Standalone backend. A worker 
> should book all the resources reserved to Spark on the host it is launched, 
> then it can allocate those resources to one or more executors launched by 
> this worker. Since each executor runs in a separated JVM, we can limit the 
> memory of each executor to avoid long GC pause.
> The remaining concern is the local-cluster mode is implemented by launching 
> multiple workers on the local host, we might need to re-implement 
> LocalSparkCluster to launch only one Worker and multiple executors. It should 
> be fine because local-cluster mode is only used in running Spark unit test 
> cases, thus end users should not be affected by this change.
> Removing multiple workers on the same host support could simplify the deploy 
> model of Standalone backend, and also reduce the burden to support legacy 
> deploy pattern in the future feature developments.
> The proposal is to update the document to deprecate the support of system 
> environment `SPARK_WORKER_INSTANCES` in 3.0, and remove the support in the 
> next major version (3.1.0).



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