YufeiLiu edited comment on FLINK-15959 at 2/14/20 5:25 PM:

I've made some modification of description according to the comments, please 
tell me if  I've missed anything. 
[~sewen] Can I take this task if the improvement is necessary.

was (Author: liuyufei):
I've made some modification of description according to the comments. Please 
tell me if  I've missed anything. 

> Add min/max number of slots configuration to limit total number of slots
> ------------------------------------------------------------------------
>                 Key: FLINK-15959
>                 URL: https://issues.apache.org/jira/browse/FLINK-15959
>             Project: Flink
>          Issue Type: Improvement
>          Components: Runtime / Coordination
>    Affects Versions: 1.11.0
>            Reporter: YufeiLiu
>            Priority: Major
> Flink removed `-n` option after FLIP-6, change to ResourceManager start a new 
> worker when required. But I think maintain a certain amount of slots is 
> necessary. These workers will start immediately when ResourceManager starts 
> and would not release even if all slots are free.
> Here are some resons:
> # Users actually know how many resources are needed when run a single job, 
> initialize all workers when cluster starts can speed up startup process.
> # Job schedule in  topology order,  next operator won't schedule until prior 
> execution slot allocated. The TaskExecutors will start in several batchs in 
> some cases, it might slow down the startup speed.
> # Flink support 
> [FLINK-12122|https://issues.apache.org/jira/browse/FLINK-12122] [Spread out 
> tasks evenly across all available registered TaskManagers], but it will only 
> effect if all TMs are registered. Start all TMs at begining can slove this 
> problem.
> *suggestion:*
> * Add config "taskmanager.minimum.numberOfTotalSlots" and 
> "taskmanager.maximum.numberOfTotalSlots", default behavior is still like 
> before.
> * Start plenty number of workers to satisfy minimum slots when 
> ResourceManager accept leadership(subtract recovered workers).
> * Don't comlete slot request until minimum number of slots are registered, 
> and throw exeception when exceed maximum.

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