David Anderson created FLINK-28975:
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Summary: withIdleness marks all streams from FLIP-27 sources as
idle
Key: FLINK-28975
URL: https://issues.apache.org/jira/browse/FLINK-28975
Project: Flink
Issue Type: Bug
Components: API / DataStream
Affects Versions: 1.15.1
Reporter: David Anderson
Fix For: 1.16.0
Using withIdleness with a FLIP-27 source leads to all of the streams from the
source being marked idle, which in turn leads to incorrect results, e.g., from
joins that rely on watermarks.
Quoting from the user ML thread:
In org.apache.flink.streaming.api.operators.SourceOperator, there are separate
instances of WatermarksWithIdleness created for each split output and the main
output. There is multiplexing of watermarks between split outputs but no
multiplexing between split output and main output.
For a source such as org.apache.flink.connector.kafka.source.KafkaSource,
{color:#353833}there is only output from splits and no output from main. Hence
the main output will (after an initial timeout) be marked as idle.{color}
{color:#353833} {color}
{color:#353833}The implementation of {color}WatermarksWithIdleness is such that
once an output is idle, it will periodically re-mark the output as idle. Since
there is no multiplexing between split outputs and main output, the idle marks
coming from main output will repeatedly set the output to idle even though
there are events from the splits. Result is that the entire source is
repeatedly marked as idle.
See this ML thread for more details:
[https://lists.apache.org/thread/bbokccohs16tzkdtybqtv1vx76gqkqj4]
This probably affects older versions of Flink as well, but that needs to be
verified.
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