Page History

...

• Default Value:
  • Hive 0.x and 1.x: false 
  • Hive 2.x and later: true (HIVE-12320)
    
• Added In: Hive 0.12.0 with HIVE-4409

If true (default is false), ALTER TABLE operations which change the type of
+ a of a column (say STRING) to an incompatible type (say MAP<STRING, STRING>) are disallowed.
+ RCFile  RCFile default serde SerDe (ColumnarSerdeColumnarSerDe) serializes the values in such a way that the
+ datatypes the datatypes can be converted from string to any type. The map is also serialized as
+ a as a string, which can be read as a string as well. However, with any binary
+ serializationbinary serialization, this is not true. Blocking the ALTER TABLE prevents ClassCastExceptions
+ when ClassCastExceptions when subsequently trying to access old partitions.
+ +

Primitive types like INT, STRING, BIGINT, etc. are compatible with each other and are
+ not are not blocked.+
+

See HIVE-4409 for more details.

hive.metastore.integral.jdo.pushdown

...