Concatenation of an external table

If the table or partition contains many small RCFiles or ORC files, then ALTER TABLE table_name [PARTITION (partition_key = 'partition_value' [, ...])] CONCATENATE will merge them into larger files. In the case of RCFile the merge happens at block level whereas for ORC files the merge happens at stripe level thereby avoiding the overhead of decompressing and decoding the data

Hive 1 and 2

You can concatenate an external table. For example:

ALTER TABLE table_name [PARTITION (partition_key = 'partition_value' [, ...])] CONCATENATE

Hive 3

Concatenation of an external table using CONCATENATE is not supported. For example, you get the following error:

alter table t6 concatenate;
Error: Error while compiling statement: FAILED: SemanticException [Error 30034]: Concatenate/Merge can only be performed on managed tables (state=42000,code=30034)

Action Required

Remove the CONCATENATE operation on external tables.

Distribution Affected

CDH5, CDH6