You can create a read test mapping to identify source bottlenecks. A read test mapping isolates the read query by removing the transformation in the mapping.
To create a read test mapping, complete the following steps:
Make a copy of the original mapping.
In the copied mapping, keep only the sources, source qualifiers, and any custom joins or queries.
Remove all transformations.
Connect the source qualifiers to a file target.
Run a session against the read test mapping. If the session performance is similar to the original session, you have a source bottleneck.