[jira] [Closed] (FLINK-17330) Avoid scheduling deadlocks caused by cyclic input dependencies between regions

["Zhu Zhu (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-17330?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Zhu Zhu closed FLINK-17330.
---------------------------
    Resolution: Fixed

Done via
c77772bb9808178f9b28742a0738280552df209f
c0f382f5f0072441ef8933f6993f1c34168004d6

> Avoid scheduling deadlocks caused by cyclic input dependencies between regions
> ------------------------------------------------------------------------------
>
>                 Key: FLINK-17330
>                 URL: https://issues.apache.org/jira/browse/FLINK-17330
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Runtime / Coordination
>            Reporter: Zhu Zhu
>            Assignee: Zhu Zhu
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.12.0
>
>
> Imagine a job like this:
> A -- (pipelined FORWARD) --> B -- (blocking ALL-to-ALL) --> D
> A -- (pipelined FORWARD) --> C -- (pipelined FORWARD) --> D
> parallelism=2 for all vertices.
> We will have 2 execution pipelined regions:
> R1 = {A1, B1, C1, D1}
> R2 = {A2, B2, C2, D2}
> R1 has a cross-region input edge (B2->D1).
> R2 has a cross-region input edge (B1->D2).
> Scheduling deadlock will happen since we schedule a region only when all its inputs are consumable (i.e. blocking partitions to be finished). This is because R1 can be scheduled only if R2 finishes, while R2 can be scheduled only if R1 finishes.
> To avoid this, one solution is to force a logical pipelined region with intra-region ALL-to-ALL blocking edges to form one only execution pipelined region, so that there would not be cyclic input dependency between regions.
> Besides that, we should also pay attention to avoid cyclic cross-region POINTWISE blocking edges. 



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