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From "Gyula Fora (JIRA)" <j...@apache.org>
Subject [jira] [Created] (FLINK-2390) Replace iteration timeout with algorithm for detecting termination
Date Tue, 21 Jul 2015 20:24:05 GMT
Gyula Fora created FLINK-2390:
---------------------------------

             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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