morningman commented on issue #66645:
URL: https://github.com/apache/doris/issues/66645#issuecomment-5254513013

   Thanks for the detailed use case. Let me make sure I understand the 
requirement correctly.
   
   One possible approach would be to implement this as a variant of federated 
query. We could potentially build it on top of the [[ADBC 
Catalog](https://doris.apache.org/docs/dev/lakehouse/catalogs/adbc-catalog)](https://doris.apache.org/docs/dev/lakehouse/catalogs/adbc-catalog),
 which is planned to replace the current Doris Catalog for this type of 
cross-Doris query.
   
   The basic idea would be:
   
   * The optimizer pushes as much computation as possible, especially 
aggregation and joins, to the remote Doris cluster, so that only the 
processed/aggregated results are returned to the local cluster.
   * For this use case, pushdown would need to be mandatory rather than just an 
optimization. If the optimizer cannot generate a remote plan that satisfies the 
data residency requirement—for example, if row-level/raw data would need to be 
returned from the remote cluster—the query should fail instead of falling back 
to fetching the raw data.
   
   At the moment, the optimizer does not yet support aggregation pushdown or 
join pushdown for this federated query path, but these are capabilities we can 
consider adding.
   
   Would this model satisfy your requirements? In particular, is it acceptable 
for a query to fail when Doris cannot generate a plan that keeps all raw data 
processing inside the remote region?


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