[jira] [Created] (DRILL-4127) HiveSchema.getSubSchema() should use lazy loading of all the table names

["Jinfeng Ni (JIRA)" <ji...@apache.org>]

Jinfeng Ni created DRILL-4127:
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             Summary: HiveSchema.getSubSchema() should use lazy loading of all the table names
                 Key: DRILL-4127
                 URL: https://issues.apache.org/jira/browse/DRILL-4127
             Project: Apache Drill
          Issue Type: Bug
            Reporter: Jinfeng Ni
            Assignee: Jinfeng Ni


Currently, HiveSchema.getSubSchema() will pre-load all the table names when it constructs the subschema, even though those tables names are not requested at all. This could cause considerably big performance overhead, especially when the hive schema contains large # of objects (thousands of tables/views are not un-common in some use case). 

In stead, we should change the loading of table names to on-demand. Only when there is a request of get all table names, we load them into hive schema.

This should help "show schemas", since it only requires the schema name, not the table names in the schema. 




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