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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