Stamatis Zampetakis created HIVE-23479:

             Summary: Avoid regenerating JdbcSchema for every table in a query
                 Key: HIVE-23479
             Project: Hive
          Issue Type: Improvement
          Components: Query Planning
            Reporter: Stamatis Zampetakis

Currently {{CalcitePlanner}} generates a complete {{JdbcSchema}} for every 
{{JdbcTable}} in the query.

This wastes some resources since every call to {{JdbcSchema#getTable}} needs to 
communicate with the database to bring back the tables belonging to the schema. 
Moreover, the fact that a schema is created during planning is 
counter-intuitive since in principle the schema shouldn't change.  

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