Limitation of FastLoad:-
FastLoad has few limitations. Many of these restrictions help FastLoad to load data in lightning fast in Teradata table.
No Secondary Index–Teradata FastLoad does not support any secondary index on the target table. This is because secondary index will create subtable block and many times on different AMP from the data row. This is an overhead and may slow down the performance of the FastLoad.
So we need to drop them before starting of the FastLoad. We can easily create them after loading the table.
create index (columnname/s) on <databasename>.<tablename>; /* Non-Unique Secondary Index */
create unique index (columnname/s) on <databasename>.<tablename>; /* Unique Secondary Index */
No Referential Integrity – Referential Integrity (RI) on the target table not supported by the Teradata FastLoad. RI requires too much system checking to maintain the referential constrains to a different table.
So prior to load the data into target table, we need to drop RI constrains.
Triggers are not allowed – Triggers are involved with the more than one table. FastLoad deals with the only one target table. Simply ALTER the Triggers to the DISABLED status prior to using FastLoad.
Duplicate rows are not supported – Multiset table will be holding duplicate rows that mean values in every columns are identical. When FastLoad finds duplicate rows, they are discarded. While FastLoad can load data into a multi-set table, FastLoad will not load duplicate rows into a multi-set table because FastLoad discards duplicate rows.
No AMP may goes down during FastLoad – If any AMP goes down during FastLoad process, that AMPs needs to be back to online to restart the FastLoad process.
Not more than one data type conversion is allowed per column – As data type conversion is a CPU intensive process, only one data type conversion is allowed for each column.
Data conversions capabilities :-
Teradata FastLoad has the capability to convert the column value before inserting into the target table. For example, an input value with character data type is targeted for date type column, FastLoad can change the input data specification to date before inserting it into the target table.
Below are the conversions allowed by the FastLoad –
- Numeric-to-numeric (for example integer-to-decimal)
- Character-to-numeric
- Character-to-date
- Date-to-character