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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4348) Implement slot allocation protocol with TaskExecutor
Date Fri, 30 Sep 2016 09:26:20 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15535527#comment-15535527

ASF GitHub Bot commented on FLINK-4348:

Github user mxm commented on the issue:

    Thanks for the feedback, @beyond1920 and @KurtYoung.
    You're right, the changes don't allow slots to be released by a TaskExecutor. We can change
that by explicitly reporting to the RM if a slot becomes free. This may also decrease latency
in case a tasks finishes and new ones are waiting to be deployed.
    >b. When we handleSlotRequestFailedAtTaskManager, we will make this slot free again.
If the slot is occupied by some other task now, we will continuously failed for all allocation
on this slot. ( this can be fixed by 3)
    How can that happen? The slot will not appear free while it is allocated at the TaskExecutor.
When allocation fails, it is marked as free and then the request is retried immediately. It
must succeed eventually if the initial decision to allocate the slot was correct. However,
we need to explicitly check if a TaskExecutor has deregistered, to make sure old TaskExecutors
don't send failures which triggers slot allocation of already removed slots (due to TaskExecutor
deregistration). That should be fix with this PR.
    > 1. We can remove the update status part entirely, since it can only do new slot registration
now, we can just move it to the task executor first registration.
    Very good suggestion. Let's move the initial registration and reconciliation of slots
to the registration message.
    To wrap up, let's change the following:
    1. Move the slot registration and allocation report to the registration of the TaskExecutor
    2. Let the TaskExecutor immediately notify the ResourceManager once a slot becomes free
    3. Change the fencing in handleSlotRequestFailedAtTaskManager to protect against TaskExecutors
which are not registered anymore.
    Let me know if that would work for you.

> 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
> 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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