IMPALA deletes data files when you issue a DROP TABLE on an internal table, but not an external one. By default, the CREATE TABLE statement creates internal tables, where the files are MANAGED by Impala. An external table is CREATED with a CREATE EXTERNAL TABLE statement, where the files reside in a location outside the control of Impala. Issue a DESCRIBE FORMATTED statement to check whether a table is internal or external. The KEYWORD MANAGED_TABLE indicates an internal table, from which Impala can delete the data files. The keyword EXTERNAL_TABLE indicates an external table, where Impala will leave the data files untouched when you drop the table.

Even when you drop an internal table and the files are removed from their original location, you might not get the hard drive space back IMMEDIATELY. By default, files that are deleted in HDFS go into a special trashcan directory, from which they are purged after a period of time (by default, 6 hours). For background information on the trashcan mechanism.

Impala deletes data files when you issue a DROP TABLE on an internal table, but not an external one. By default, the CREATE TABLE statement creates internal tables, where the files are managed by Impala. An external table is created with a CREATE EXTERNAL TABLE statement, where the files reside in a location outside the control of Impala. Issue a DESCRIBE FORMATTED statement to check whether a table is internal or external. The keyword MANAGED_TABLE indicates an internal table, from which Impala can delete the data files. The keyword EXTERNAL_TABLE indicates an external table, where Impala will leave the data files untouched when you drop the table.

Even when you drop an internal table and the files are removed from their original location, you might not get the hard drive space back immediately. By default, files that are deleted in HDFS go into a special trashcan directory, from which they are purged after a period of time (by default, 6 hours). For background information on the trashcan mechanism.