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https://issues.apache.org/jira/browse/FLINK-4348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15535565#comment-15535565
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ASF GitHub Bot commented on FLINK-4348:
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Github user KurtYoung commented on the issue:
https://github.com/apache/flink/pull/2571
@mxm I think that situation will happen when RM request slot from TM, TM
accept the request, but the response was somehow missed. Typically, when an rpc
error occurred, the send could not know whether the receiver handles that
request or not.
The changes looks good to me.
> Implement slot allocation protocol with TaskExecutor
> ----------------------------------------------------
>
> Key: FLINK-4348
> URL: https://issues.apache.org/jira/browse/FLINK-4348
> Project: Flink
> Issue Type: Sub-task
> Components: Cluster Management
> Reporter: Kurt Young
> Assignee: Maximilian Michels
>
> When slotManager finds a proper slot in the free pool for a slot request,
> slotManager marks the slot as occupied, then tells the taskExecutor to give
> the slot to the specified JobMaster.
> when a slot request is sent to taskExecutor, it should contain following
> parameters: AllocationID, JobID, slotID, resourceManagerLeaderSessionID.
> There exists 3 following possibilities of the response from taskExecutor, we
> will discuss when each possibility happens and how to handle.
> 1. Ack request which means the taskExecutor gives the slot to the specified
> jobMaster as expected.
> 2. Decline request if the slot is already occupied by other AllocationID.
> 3. Timeout which could caused by lost of request message or response message
> or slow network transfer.
> On the first occasion, ResourceManager need to do nothing. However, under the
> second and third occasion, ResourceManager need to notify slotManager,
> slotManager will verify and clear all the previous allocate information for
> this slot request firstly, then try to find a proper slot for the slot
> request again. This may cause some duplicate allocation, e.g. the slot
> request to TaskManager is successful but the response is lost somehow, so we
> may request a slot in another TaskManager, this causes two slots assigned to
> one request, but it can be taken care of by rejecting registration at
> JobMaster.
> There are still some question need to discuss in a step further.
> 1. Who send slotRequest to taskExecutor, SlotManager or ResourceManager? I
> think it's better that SlotManager delegates the rpc call to ResourceManager
> when SlotManager need to communicate with outside world. ResourceManager
> know which taskExecutor to send the request based on ResourceID. Besides this
> RPC call which used to request slot to taskExecutor should not be a
> RpcMethod, because we hope only SlotManager has permission to call the
> method, but the other component, for example JobMaster and TaskExecutor,
> cannot call this method directly.
> 2. If JobMaster reject the slot offer from a TaskExecutor, the TaskExecutor
> should notify the free slot to ResourceManager immediately, or wait for next
> heartbeat sync. The advantage of first way is the resourceManager’s view
> could be updated faster. The advantage of second way is save a RPC method in
> ResourceManager.
> 3. There are two communication type. First, the slot request could be sent as
> an ask operation where the response is returned as a future. Second,
> resourceManager send the slot request in fire and forget way, the response
> could be returned by an RPC call. I prefer the first one because it is more
> simple and could save a RPC method in ResourceManager (for callback in the
> second way).
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