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https://issues.apache.org/jira/browse/SPARK-33418?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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dingbei updated SPARK-33418:
----------------------------
    Description: 
It begins with the needs to  start a lot of spark streaming receivers .  *The 
launch time gets super long when it comes to more than 300 receivers.* I will 
show tests data I did and how I improved this.

*Tests preparation*

There are two cores exists in every executors.(one for receiver and the other 
one to process every batch of datas). I observed launch time of all receivers 
through  spark web UI (duration between the first receiver started to the last 
one started).

*Tests and data*

At first, we set the number of executors to 200 which means to start 200 
receivers and everything goes well. It takes about 50s to launch all receivers.

Then we set the number of executors to 500 which means to start 500 receivers. 
The launch time became around 5 mins.

 *Dig into souce code*

Then I start to look for the reason in the source code.  I use Thread dump to 
check which methods takes relatively long time. Then I type logs between these 
methods. At last I find that The loop in TaskSchedulerImpl.resourceOffers will 
executes more than 

  was:
It begins with the needs to  start a lot of spark streaming receivers .  *The 
launch time gets super long when it comes to more than 300 receivers.* I will 
show tests data I did and how I improved this.

*Tests preparation*

There are two cores exists in every executors.(one for receiver and the other 
one to process every batch of datas). I observed launch time of all receivers 
through  spark web UI (duration between the first receiver started to the last 
one started).

*Tests and data*

At first, we set the number of executors to 200 which means to start 200 
receivers and everything goes well. It takes about 50s to launch all receivers.

Then we set the number of executors to 500 which means to start 500 receivers. 
The launch time became around 5 mins.

 *Dig into souce code*

Then I start to look for the reason in the source code.  I use Thread dump to 
check which methods takes relatively long time. Then I type logs between these 
methods. At last I find that The loop in 


> TaskSchedulerImpl: Check pending tasks in advance when resource offers
> ----------------------------------------------------------------------
>
>                 Key: SPARK-33418
>                 URL: https://issues.apache.org/jira/browse/SPARK-33418
>             Project: Spark
>          Issue Type: Improvement
>          Components: Spark Core
>    Affects Versions: 3.0.1
>            Reporter: dingbei
>            Priority: Major
>
> It begins with the needs to  start a lot of spark streaming receivers .  *The 
> launch time gets super long when it comes to more than 300 receivers.* I will 
> show tests data I did and how I improved this.
> *Tests preparation*
> There are two cores exists in every executors.(one for receiver and the other 
> one to process every batch of datas). I observed launch time of all receivers 
> through  spark web UI (duration between the first receiver started to the 
> last one started).
> *Tests and data*
> At first, we set the number of executors to 200 which means to start 200 
> receivers and everything goes well. It takes about 50s to launch all 
> receivers.
> Then we set the number of executors to 500 which means to start 500 
> receivers. The launch time became around 5 mins.
>  *Dig into souce code*
> Then I start to look for the reason in the source code.  I use Thread dump to 
> check which methods takes relatively long time. Then I type logs between 
> these methods. At last I find that The loop in 
> TaskSchedulerImpl.resourceOffers will executes more than 



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