Wrapped metanodes in loops

Hi all,

is there some documentation about which loops work well when containing wrapped meta nodes with streaming?

In my experience, it is possible to use wrapped meta nodes within Group Loops, but they will fail in Chunk Loops as well as in Prallel Chunk Loops. Is there any more detailed information available?





Can you clarify which problems you have run into? There was a very recent fix related to file stores (used in images) / loops / wrapped metanodes. The change is already online (https://tech.knime.org/changelog-v310). It was put online yesterday!

Can you update, try again and then report your findings?


Hi Bernd,

that's good news, thanks for letting me know.

The problem I still have specifically is with Parallel Chunk Start and End loops that contain both meta nodes and wrapped meta nodes. When running the workflow, I get:

ERROR Load and resize images 0:243:285  Caught "NullPointerException": null

with a wrapped meta node that contains an Image Reader and an Image Resizer node. This node configuration runs well when I use it without the parallel loops, but with them, it seems as the main branch is running through without problems, but the automatically created Parallel Chunks meta node is still executing while the Parallel Chunk End already fails with an error:

ERROR Parallel Chunk End   0:242      Execute failed: Not all chunks finished - check individual chunk branches for details.

I'll try to assemble a minimal example workflow tomorrow, since my current workflow is too involved for uploading it.


Any ideas?



I attached a small workflow illustrating the issue. Wrapped metanodes in a Parallel Chunk Loops don't seem to get executed, instead failing with a NullPointerException.

Please let me know if you need further information debugging this issue.



Hi Jan,

Thanks for the detailed analysis and the workflow. The problem has already been fixed and was planned to be delivered with the next feature release (3.2 ... due in summer). It's a one-liner so happy to backport and make it available in 3.1.2.

- Bernd

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Hi Bernd,

Great, thanks a lot!