Table Reader: Execute failed: Writing to table process threw "ClassCastException"

[mwiegand]

Hi,

I once raised this bug but it got closed before feedback about the “ClassCastException” issue was given. I want to bring this to your attention again as, when this error occurs, which it did again unexpectedly now w/o any particular change made, the whole execution and results must get discarded.

Though, I am able to limit the amount of rows read which indicates “garbage” data being written somewhere at the end, likely during the previous loop iteration, to the table.

ERROR Table Reader 6:1126:0:1018:0:1007 Execute failed: Writing to table process threw "ClassCastException"

Table Reader Caches Columns breaking workflow execution

Hi, I erratically face an issue I struggle to reproduce to help fixing it. Whilst I have a pretty good understanding and explanation to the circumstances, I still can not reproduce it in a workflow to share with you (but soon might have). The issue When a Table Reader initially reads a table, it seems to cache it’s columns as well as it’s column data types. Regardless if any transformation happens, the table reader, after the table being read was altered (column count, column type change), t…

Attached the Thread Dump. I have backed up the table file but can only share it privately due to client data being present.

231010-knime-thread-dump-ClassCastException.txt (330.3 KB)

I can share the table files, as done before, via a private download link. Please reach out to me per DM or email as usual.

PS: I have already isolated the data which triggers the issue and can reproduce it. I am currently trying to create a workflow with anatomized data which I can share.

PPS: It is caused by the JSON data. Albeit it’s valid JSON data, verified by Knime converting it to JSON and an external JSON validator, there is partially escaped JSON in the form of a string in a JSON key.

test-json-ClassCastException.txt (27.9 KB)

However, using that exact same setup in the test workflow I hereby share, it is NOT reproducible anymore. Applying the fallback from the other post linked at the top, replacing each character by itself, the table reader works (bcs it converts JSON to String). Reading the data also works, even when nothing got replaced, if the column type string is set.

Table Reader JSON triggers ClassCastException – mwiegand

Best
Mike

[armingrudd]

Hi @mwiegand,
I didn’t quite understand the issue here. I can execute the provided worklow without any issues. Both Table Reader nodes execute successfully.
I’m not sure if your issue is the truncated json or not. But we truncate long values to prevent long loading in port view. The data is not manipulated at all. You can test it with a JSON Path node after the Table Reader with JSON.

[mwiegand]

Hi @armingrudd,

yes, that’s what I mentioned as well that when copying nodes from one workflow to another, the issue is not reproducible. Only in the original workflow, the JSON string seems to cause the issue.

Best
Mike

[armingrudd]

I think I could reproduce the problem.

Would you check if the issue you have mentioned occurs while the workflow is running in columnar backend?

I didn’t get the same error message you mentioned and the Table Reader node doesn’t fail but it cannot read the JSON if the JSON is too long and the workflow is configured to columnar backend. I created a ticket for this issue: AP-21249

[mwiegand]

Glad to hear. How did you reproduced that rather elusive issue? The workflow runs with the current default row based backend.

PS: The test workflow and the workflow where it originated both use the row based backend.

[armingrudd]

What happens if you use the provided data here in the original workflow?
I mean, can you reproduce the issue if you change the data in the original workflow? (So you can share a workflow which reproduces the problem you mentioned).

@mwiegand

How did you reproduced that rather elusive issue?

Just used your workflow and tried to reproduce the problem. Thank you for helping.