Python Nodes: Fail to execute when run concurrently

Sometimes when running Python nodes at the same time it can happen that a node just fails with “stopped executing”. I wasn’t able to pin-point the exact issue but I think it’s when 2 nodes at the same time are loading / outputting data, then one of the fails.


WARN Python Learner 0:579:0:423 Execution canceled

And log file doesn’t say anything more.

So there for sure something is going wrong (not 100% stable) with the python nodes.

Hi @beginner,

Thanks for letting us know. Just to make sure: Which OS are you using and which KNIME version? We’ll try to track down and fix the problem.



Windows Server 2012 R2 (64-bit)

KNIME 3.5.2

With apache arrow for serialization

Reproduction is non-trivial as I’m not sure what causes it.

Error also happens with flat buffers as serialization.

Hi @beginner,

we were able to reproduce the issue (with some pyhton nodes in a parallel chunk loop) and work on a solution.Thanks again!


Similar issue occurs with Python node (Python 3.6) that is inside of a loop. The node spontaneously gets canceled.
Systems: Windows 8.1 Enterprise
KNIME Version: 3.6.0

Console details, at point of error:

ERROR PythonKernel C:\Program Files\Python36\lib\site-packages\sklearn\utils\ DataConversionWarning: A column-vector y was passed when a 1d array was expected. Please change the shape of y to (n_samples, ), for example using ravel().
DEBUG PythonKernel y = column_or_1d(y, warn=True)
WARN Python Script (1⇒1) 0:3100:3219:3119 Execution canceled

If I re-run the node, it works…

The issue should be fixed with KNIME 3.6.1. Please let us know if you still experience any problems once it’s released :slight_smile:.

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