Unused metanode input makes workflow unsaveable/ unloadable

Dear KNIME-ers,

The last few days I have been struggling with a strange error. My workflow seemed to run well, it seemed to save correctly, but when I reloaded it, many nodes had gone from executed (green) to yellow/red (configured/unconfigured) again, undoing my lengthy calculations.

I finally managed to isolate the source of the error to a metanode somewhere in the middle of the workflow. It had two inputs, of which the second one was not connected to anything. It was simply there to allow for possible future extra input.

The fact that this unused input was present made it impossible to save/load the data of nodes after this metanode.

Is this a bug or intended behaviour?

I attach a simple example workflow where the error can be reproduced. Execute all nodes, save, close, load. After this sequence of events, node 7 and node 10 will have reverted from "excuted" to "configured".






I strongly believe it is by design. There is no point in having a metanode with an unused port reserved for "future use" considering you can always add/remove ports from a metanode at any time if necessary (with Reconfigure...)

I find it more valuable that the metanode, which could be deep inside a much larger workflow, informs you that you forgot to connect one of its port by preventing the execution. This behavior preserves the integrity of the workflow and of its results.

Would you want the workflow to still run if you had actually forgotten to connect some of the intended inputs to its metanodes?


I wouldn't mind if it is by design, indeed if only it would give a proper error message, instead of making me think that my calculations are saved.

However, I can work around this bug/feature by connecting the second unused input connector of the metanode to a dummy node (for example a column filter) inside the metanode. Then everything saves/loads normally, even though this dummy node is itself not connected to anything else. This makes me think that it is not by design.


I was bitten again by this bug/feature, took me an hour to figure out what was going on. I wanted to write a new bug report and then discovered that I posted about it before. I must be getting old.

On the bright side, the “suggested post” feature of the Knime forum works really well :smile:


Hi there!

Just an info on this one. This has been reported and hopefully will be soon fixed.

Glad to know suggested post feature does what it should :slight_smile:


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That’s great, thank you! :smiley: This bug is a real headscratcher when it happens.

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Hi @Aswin,

no more head scratching for this one as it has been fixed with KNIME 4.2.0 version :wink:


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Dear @ipazin

Thank you guys! :smiley:


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