Returns the data contained in this part in the form of an iterator.
Returns the data contained in this part in the form of an iterator. This function should return a new iterator on each invocation. The iterator can be lazily initialized to the first read if required.
A Part represents part of the source data. Eg a single file in a multi-file source, or a single table in a multi-table source. Splitting sources into parts allows them to be read concurrently, therefore, implementations must ensure that different parts can be safely read in parallel. A single part is always read by a single thread.