AnishMahto opened a new pull request, #55996:
URL: https://github.com/apache/spark/pull/55996

   Approved AutoCDC SPIP: 
https://lists.apache.org/thread/j6sj9wo9odgdpgzlxtvhoy7szs0jplf7
   
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   This is a stacked PR. Review incremental diff here: 
https://github.com/AnishMahto/spark/compare/SPARK-56923-SCD1-merge-microbatch-onto-auxiliary...SPARK-56927-SCD1-merge-microbatch-onto-target
   --------
   
   
   Preamble:
   
   The SCD type 1 flow is a foreachBatch streaming query on an input 
change-data-feed, and is responsible for reconciling the incoming change data 
onto some target table that follows SCD1 replication semantics.
   
   SCD1 flows also maintain an "auxiliary" table to keep track of 
early-arriving out-of-order received events state. Each microbatch will need to 
reconcile against this auxiliary table as well, and update the auxiliary 
table's state appropriately for future microbatches.
   
   
   
   
   Merge Microbatch onto Target:
   
   The final part of an SCD1 reconciliation - merge the reconciled dataframe 
(deduplicated, target columns and operational metadata projected, and tombstone 
applied) onto the target table.
   
   The target table's contents represent the SCD1 transformation of the change 
data feed, for the specified target column selection in the `ChangeArgs`.
   
   Merging onto the target under SCD1 semantics means deleting existing rows 
that match against the reconciled microbatch's delete events, and inserting or 
updating rows as appropriate for the reconciled microbatch's upsert events.


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