Hive has 2 types of UDFs. This commit contains limited
support for the second generation UDFs called GenericUDFs.
The main limitations are as follows:
Decimal types are not supported. The Impala framework determines
the precision and scale of the decimal return type. However, the
Hive GenericUDFs allow the capability to choose its own return
type based on the parameters. Until this can be resolved, it is
safer to forbid decimals from being used. Note that this
limitation currently exists in the first generation of Hive Java
UDFs.
Complex types are not supported.
Functions are not extracted from the jar file. The first generation
of Hive UDFs allowed this because the method prototypes are
explicitly defined and can be determined at function creation time. For
GenericUDFs, the return types are determined based on the parameters
passed in when running a query.
For the same reason as above, GenericUDFs cannot be made permanent.
They will need to be recreated everytime the server is restarted.
This is a severe limitation and will be resolved in the near future.
Change-Id: Ie6fd09120db413fade94410c83ebe8ff104013cd
Reviewed-on: http://gerrit.cloudera.org:8080/18295
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
Reviewed-by: Csaba Ringhofer <csringhofer@cloudera.com>
