DRILL-7095: Expose table schema (TupleMetadata) to physical operator (EasySubScan) 1. Add system / session option store.table.use_schema_file to control if file schema can be used during query execution. False by default. 2. Added methods in StoragePlugin interface which allow to create Group Scan with provided table schema. 3. EasyGroupScan and EasySubScan now contain table schema, also they are able to serialize / deserialize it along with other scan properties. 4. DrillTable which is the main entry point for schema provisioning, has method to store schema and later uses it to create physical scan. 5. WorkspaceSchema when returning Drill table instance will get table schema from table root if available and if store.table.use_schema_file is set to true.
This PR is the next step for Schema Provisioning project which currently exposes schema only for text reader.