Github user MikeThomsen commented on the issue:
https://github.com/apache/nifi/pull/2448
@pvillard31 I found that a catch block was suppressing a critical problem
with how I was handling the input flowfile. When I'd call `session.commit()`
after a block of results were written to a flowfile, it would throw an
exception because the input flowfile had not been transferred yet.
So what I am going to do is redo this to make it configurable again. With
the default behavior being only one single commit. Then users can choose a
"streaming mode" where at the the first sign of success it transfers the input
flowfile to REL_ORIGINAL. Then if an error happens, it would write a new
flowfile with the same attributes and content as the original and send that
cloned copy to the failure relationship. It may not be perfect, but I don't
think NiFi has a way to do a partial commit which is what I'd need to make it
work as-is.
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