Matthias J. Sax created KAFKA-12718:
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Summary: SessionWindows are closed too early
Key: KAFKA-12718
URL: https://issues.apache.org/jira/browse/KAFKA-12718
Project: Kafka
Issue Type: Bug
Components: streams
Reporter: Matthias J. Sax
SessionWindows are defined based on a {{gap}} parameter, and also support an
additional {{grace-period}} configuration to handle out-of-order data.
To incorporate the session-gap a session window should only be closed at
{{window-end + gap}} and to incorporate grace-period, the close time should be
pushed out further to {{window-end + gap + grace}}.
However, atm we compute the window close time as {{window-end + grace}}
omitting the {{gap}} parameter.
Because default grace-period is 24h most users might not notice this issues.
Even if they set a grace period explicitly (eg, when using suppress()), they
would most likely set a grace-period larger than gap-time not hitting the issue
(or maybe only realize it when inspecting the behavior closely).
However, if a user wants to disable the grace-period and sets it to zero (on
any other value smaller than gap-time), sessions might be close too early and
user might notice.
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