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https://issues.apache.org/jira/browse/FLINK-8566?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Timo Walther updated FLINK-8566:
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> Replace retract/insert of same record for state retention timer resets
> ----------------------------------------------------------------------
>
> Key: FLINK-8566
> URL: https://issues.apache.org/jira/browse/FLINK-8566
> Project: Flink
> Issue Type: Improvement
> Components: Table SQL / Planner
> Affects Versions: 1.5.0
> Reporter: Fabian Hueske
> Priority: Minor
>
> Currently a simple query like {{SELECT DISTINCT a, b, c FROM tableX}} is
> translated into a plan that generates a retraction stream. However, one would
> assume that an append stream should be possible as well. In fact, the plan
> doesn't produce actual updates.
> Internally, the {{DISTINCT}} is translated into a {{GROUP BY}} with all
> distinct fields being keys and no aggregation functions. The corresponding
> operator produces updates, because aggregation function might update their
> results as new records are received. So we could just implement a dedicated
> operator for {{DISTINCT}}. However, this would not work if a user configures
> a state retention time. In this case, we emit retraction/insert messages for
> the same (distinct) record whenever a new row is received to reset the state
> clean-up timers of the downstream operators.
> One way to solve this issue to implement a dedicated mechanism to update
> state clean-up timers for unchanged records instead of sending out
> retraction/insert messages with identical records. This mechanism would just
> be used to reset the timers and could also be used for append streams. For
> example, we could replace the boolean flag in CRow with a byte that can take
> more than two values.
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