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FLIP-292 [1] expands the functionality of CompiledPlan to enable the configuration of operator-level state TTL by modifying the JSON file. During the discussion, it was mentioned that the SQL hint solution could also address some specific simple scenarios, which are very user-friendly, convenient, and unambiguous to use [2]. While in this FLIP, we propose to support this feature.

Specifically, we aim to support using SQL hints to configure state TTL for stream regular join [3] and group aggregate [4], which are the most typical use cases with unambiguous semantics and hint propagation. We have excluded other use cases as the hint propagation mechanism is more complex, and we might want to tackle them after the current design reaches a consensus.

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Currently, SqlToRelConverter will attach an alias hint at the root of the query block if the join hint is detected (see SqlToRelConverter.java#L2289), and then ClearJoinHintWithInvalidPropagationShuttle will ensure no join hint is propagated to the inner query block, clear the invalid hints that propagated from the outer query block by checking the hint strategy , and comparing the relative inherit path compared to the query block's alias hint. This ensures that hints from other nodes will not be attached to the current join node.

The STATE_TTL hint will apply a similar approach, which means the hint only affects the current query block and does not affect the state TTL in the subquery and view, which aligns with the current hint behavior. Likewise,  `ClearJoinHintWithInvalidPropagationShuttle` will override the visit method to remove the propagated hints for FlinkLogicalAggregate.

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