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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Describe the problems you are trying to solve.

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

Proposed Changes

Currently, the Flink cluster only requests Task Managers (TMs) when there is a resource requirement, and idle TMs are released after a certain period of time. However, in certain scenarios, we need to improve the efficiency of job execution by maintaining a certain number of available resources in the system. For example:

1. For session clusters running short lived-jobs like OLAP, we should treat session clusters as a long-running service. Having running workers all the time can greatly improve the service stability and reduce the job's cold-start latency;

2. For application mode, batch job might be scheduled stage by stage. If the next region requires more resources, it might take more time to pull up required resources. If users actually know how many resources are needed when running a single job, initialize all workers when cluster starts can speed up the resource allocation process;

Public Interfaces

Notice: Like the maximum resource options, the minimum resource options will also be invalidated in standalone clusters.

Proposed Changes

Minimum required resource check in DefaultResourceAllocationStrategy

The minimum resource limitation will be implemented in the DefaultResourceAllocationStrategy of FineGrainedSlotManager.

Each time when SlotManager needs to reconcile the cluster resources or fulfill job resource requirements, the DefaultResourceAllocationStrategy will check if the minimum resource requirement has been fulfilled. If it is not, DefaultResourceAllocationStrategy will request new PendingTaskManagers and FineGrainedSlotManager will allocate new worker resources accordingly.

Notice: The minimum resource limitation will be fulfilled in the best effort manner. The unfulfilled request will be retried in the next resource check but will not block job scheduling.

Resource stability check in SlotManagerConfiguration

After minimum required resource options are introduced, users can configure both minimum and maximum required resources in SlotManager, which might lead to worker resource oscillation. Here is an example:

taskmanager.numberOfTaskSlots: 5
slotmanager.number-of-slots.min: 11
slotmanager.number-of-slots.max: 14

In this case, the minimum required worker number derived from DefaultResourceAllocationStrategy is 3 but this will exceed the max total resource limit, which is 14 slots.

To avoid this oscillation, we need to check the worker number derived from minimum and maximum resource configuration is consistent before starting SlotManager.

Notice: The resource stability check will be disabled when the minimum resource option is 0 which is set as defaultDescribe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
• If we are changing behavior how will we phase out the older behavior?
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Test Plan

•   No

Test Plan

UT & Manually verify that the min resource limitation is working as expected.Describe in few sentences how the FLIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Rejected Alternatives

If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.