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Interoperability between Hive and Impala

This topic describes the changes made in CDP for the optimal interoperability between Hive and Impala for the improved user experience.

Statistics Interoperability Between Hive and Impala

New default behavior:

Statistics for tables are engine specific, namely, Hive or Impala, so that each engine could use its own statistics and not overwrite the statistics generated by the other engine.

When you issue the COMPUTE STATS statement on Impala, you need to issue the corresponding statement on Hive to ensure both Hive and Impala statistics are accurate.

Impala COMPUTE STATS command does not overwrite the Hive stats for the same table.

Steps to switch to the CDH behavior:

There is no workaround.

Hive Default File Format Interoperability

New default behavior:

The managed tables created by Hive are of ORC file format, by default, and support full transactional capabilities. If you create a table without specifying the STORED AS clause and load data from Hive, then such tables are not readable or writable by Impala. But Impala can continue to read non-transactional and insert-only transactional ORC tables.

Steps to switch to the CDH behavior:

  • You must use the STORED AS PARQUET clause when you create tables in Hive if you want interoperability with Impala on those tables.
  • If you want to change this default file format at the system level, in the Hive_on_Tez service configuration in Cloudera Manager, set the hive_default_fileformat_managed field to parquet.

Impala supports a number of file formats used in Apache Hadoop. It can also load and query data files produced by other Hadoop components such as hive. After upgrading from any CDH 5.x version to Cloudera Private Cloud Base 7.1, if you create a RC file in Hive using the default LazyBinaryColumnarSerDe, Impala will not be able to read the RC file. However you can set the configuration option of hive.default.rcfile.serde to ColumnarSerDe to maintain the interoperability between hive and impala.

Managed and External Tablespace Directories

New default behavior:

In CDP, there are separate HDFS directories for managed and external tables.
  • The data files for managed tables are located in warehouse location specified by the Cloudera Manager configuration setting, hive_warehouse_directory.
  • The data files for external tables are located in warehouse location specified by the Cloudera Manager configuration setting, hive_warehouse_external_directory.

If you perform file system level operations for adding/removing files on the table, you need to consider if its an external table or managed table to find the location of the table directory.

Steps to switch to the CDH behavior:

Check the output of the DESCRIBE FORMATTED command to find the table location.