junmuz commented on PR #9822:
URL: https://github.com/apache/paimon/pull/9822#issuecomment-6019029931

   @JingsongLi  Thanks for the detailed reproductions. All three are addressed 
as of 36ba0fba5.
   
     1. [P1] Drop aliasing: Metadata field IDs are now allocated above 
TableSchema#highestFieldId(), so they never reuse a dropped field's ID. 
ChangelogEventMetadataSchemaEvolutionTest reproduces your Parquet/Avro DROP 
scenario on both the merged and raw read paths.
   
     2. [P2] Historical type cast: Each file's metadata fields now use the 
source column's type from that file's schema, so schema evolution casts them 
like the source column. testSourceTypeChangeCastsHistoricalMetadata covers your 
BIGINT → DECIMAL case on Parquet/Avro.
   
     3. [P2] Sink materialization: The docs now explain why retractions with 
metadata cannot be matched by full-row comparison, and require keeping sink and 
source keys equal or using upsert-materialize=NONE, with TRY_RESOLVE as a 
safeguard. The example shows the explicit source-to-sink mapping. 
LookupChangelogEventMetadataITCase covers both the NONE and TRY_RESOLVE cases.
   
   One behavior change: renaming or dropping a column listed in 
changelog-producer.event-metadata-fields is now rejected, because it would 
silently change metadata names that downstream jobs reference. Remove the 
column from the option first.
   
   On Spark scope: I'm happy to split the Spark changes into a follow-up PR if 
you'd still prefer that.


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