[GitHub] [flink] lincoln-lil commented on pull request #20745: [FLINK-28988] Don't push filters down into the right table for temporal join

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lincoln-lil commented on PR #20745:
URL: https://github.com/apache/flink/pull/20745#issuecomment-1324621288

   > 
   
   @shuiqiangchen  another case we need to consider: 
   for an upsert source, e.g., upsert-kafka, 
   1. without this (partial) filter pushdown optimization, when the upsert key of source is same as the join key, then the execution plan can be optimized to upsert mode (does not require UB message)
   2. while after this optimization, the filter pushed down will instead degrade the upsert mode to retract mode, the corresponding upsert-kafka source will add an expensive materialization node `ChangelogNormalize` to keep the correctness(more details in FLINK-9528)
   
   currently it is hard to tell which of these two choices maybe better for all use cases. 
   And for the 2nd pattern, if we try to de-optimize in this bad pushdown case, the filter pull-up will make things more complicated, this is the biggest concern 


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