[jira] [Created] (FLINK-2390) Replace iteration timeout with algorithm for detecting termination

["Gyula Fora (JIRA)" <ji...@apache.org>]

Gyula Fora created FLINK-2390:
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             Summary: Replace iteration timeout with algorithm for detecting termination
                 Key: FLINK-2390
                 URL: https://issues.apache.org/jira/browse/FLINK-2390
             Project: Flink
          Issue Type: New Feature
          Components: Streaming
            Reporter: Gyula Fora
             Fix For: 0.10


Currently the user can set a timeout which will shut down the iteration source/sink nodes if no new data is received during that time to allow program termination in iterative streaming jobs.

This method is used due to the non-trivial nature of termination in iterative streaming jobs. While termination is not a main concern in long running streaming jobs, this behaviour makes iterative tests non-deterministic and they often fail on travis due to the timeout. Also setting a timeout can cause jobs to terminate prematurely.

I propose to remove iteration timeouts and replace it with the following algorithm for detecting termination:

-We first identify loop edges in the jobgraph (the channels from the iteration sources to the head operators)
-Once the head operators (the ones with loop input) finish with all their non-loop inputs they broadcast a marker to their outputs.
-Each operator will broadcast a marker once it received a marker from all its non-finished inputs
-Iteration sources are terminated when they receive 2 consecutive markers without receiving any record in-between

The idea behind the algorithm is to find out when no more outputs are generated from the operators inside an iteration after their normal inputs are finished.



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