While designing DataStage jobs need to consider only columns which are required and unnecessary column
propagation is not done. Columns, which are not needed in the job flow,
should not be propagated from one stage to another and from one job to
the next. It means keep RCP away from the Job "BUT" there are areas where this comes handy in processing.When you need to handle undefined columns that you encounter when the job is run, and propagate these columns through to the rest of the job RCP (Runtime Column Propagation) is the way forward. This check box enables the
feature, to actually use it you need to explicitly select the option on
each stage
If runtime column propagation is enabled in the
DataStage Administrator, you can select the Runtime column propagation
to specify that columns encountered by a stage in a parallel job can be
used even if they are not explicitly defined in the meta data. You
should always ensure that runtime column propagation is turned on if you
want to use schema files to define column meta data.
RCP Set at DataStage Adminstrator:RCP Set at DataStage Stage Output:
Here are few areas where RCP can make difference
Merge Stage & Lookup Stage:
Ensure required column meta data has been specified (this may be omitted altogether if you are relying on
Runtime Column Propagation).
Shared Container:
When inserted in a job, a shared container instance already has meta
data defined for its various links. This meta data must match that on
the link that the job uses to connect to the container exactly in all
properties. The Inputs page enables you to map meta data as required.
The only exception to this is where you are using runtime column
propagation (RCP) with a parallel shared container. If RCP is enabled
for the job, and specifically for the stage whose output connects to the
shared container input, then meta data will be propagated at run time,
so there is no need to map it at design time.
For parallel shared
containers, you can take advantage of runtime column propagation to
avoid the need to map the meta data. If you enable runtime column
propagation, then, when the jobs runs, meta data will be automatically
propagated across the boundary between the shared container and the
stage(s) to which it connects in the job.
Again "Do use RCP" when you need to propagate these "un-knowns" else processing additional columns for large data means utilization of precious resources and time on "un-wanted data".