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From "zhangjing (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4478) Implement heartbeat logic
Date Fri, 26 Aug 2016 04:03:20 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4478?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15438437#comment-15438437

zhangjing commented on FLINK-4478:

Good abstraction.

> Implement heartbeat logic
> -------------------------
>                 Key: FLINK-4478
>                 URL: https://issues.apache.org/jira/browse/FLINK-4478
>             Project: Flink
>          Issue Type: Improvement
>          Components: Distributed Coordination
>    Affects Versions: 1.1.0
>            Reporter: Till Rohrmann
>             Fix For: 1.2.0
> With the Flip-6 refactoring, we'll have the need for a dedicated heartbeat component.
The heartbeat component is used to check the liveliness of the distributed components among
each other. Furthermore, heartbeats are used to regularly transmit status updates to another
component. For example, the TaskManager informs the ResourceManager with each heartbeat about
the current slot allocation.
> The heartbeat is initiated from one component. This component sends a heartbeat request
to another component which answers with an heartbeat response. Thus, one can differentiate
between a sending and a receiving side. Apart from the triggering of the heartbeat request,
the logic of treating heartbeats, marking components dead and payload delivery are the same
and should be reusable by different distributed components (JM, TM, RM).
> Different models for the heartbeat reporting are conceivable. First of all, the heartbeat
request could be sent as an ask operation where the heartbeat response is returned as a future
on the sending side. Alternatively, the sending side could request a heartbeat response by
sending a tell message. The heartbeat response is then delivered by an RPC back to the heartbeat
sender. The latter model has the advantage that a heartbeat response is not tightly coupled
to a heartbeat request. Such a tight coupling could cause that heartbeat response are ignored
after the future has timed out even though they might still contain valuable information (receiver
is still alive).
> Furthermore, different strategies for the heartbeat triggering and marking heartbeat
targets as dead are conceivable. For example, we could periodically (with a fixed period)
trigger a heartbeat request and mark all targets as dead if we didn't receive a heartbeat
response in a given time period. Furthermore, we could adapt the heartbeat interval and heartbeat
timeouts with respect to the latency of previous heartbeat responses. This would reflect the
current load and network conditions better.
> For the first version, I would propose to use a fixed period heartbeat with a maximum
heartbeat timeout before a target is marked dead. Furthermore, I would propose to use tell
messages (fire and forget) to request and report heartbeats because they are the more flexible
model imho.

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