Hi Harish,
Optimized load is much faster and therefore preferable, especially for larger data sets. Optimized loads are possible if no transformations (calculations) are made during the load, and no (almost) filtering is done in a WHERE clause. The only acceptable filter is using function Exists: WHERE Exists(Field)
So for example this load can't be optimized: Load * From ... WHERE Country = 'US'
but this load can be optimized: Load * From ... WHERE EXISTS(Country)
On the other hand, the only time you want the load not to be optimized, is if you load a Mapping table from a QVD file. In this case, Optimized load doesn't quite work, so you want to make the load non-optimized deliberately.
Some examples of things that will cause a non-optimised load are:
- Adding new fields to the table
- Deriving new values from a field in the QVD
- Retrieving a field twice
- Most WHERE conditions
- Joining to an existing in memory table
- Loading data into a mapping table
In contrast the things you are allowed to do are:
- Rename fields
- Omit fields
- Do a simple one field WHERE EXISTS on a field returned in the record set
Regards
Neetha
