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A table operator handed a port that carried no rows loses every column

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Since Sep 10, 2026.

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Description

What happened?

A port can finish having carried no rows. An upstream filter that matches nothing still ends its channel, and DataProcessor calls on_finish either way. TableOperator then builds its table out of no tuples, and since Table.from_tuple_likes reads the column names off the tuples it is given, the operator is handed a DataFrame with no columns at all rather than the declared columns with no rows under them.

Every table operator that names one of its own columns raises KeyError on that column. Sort is the plainest case, but this reaches the visualization operators and any user-written UDFTableOperator as well. The expected behaviour is the one the schema already describes: the port's declared columns, empty.

How to reproduce?

Build a workflow of CSV File Scan, then Filter with a condition no row satisfies, then Sort on one of the scanned columns, and run it. Sort fails with KeyError naming the sort column, even though that column exists on the link.

The same thing shows without the engine, from the Python worker's own models. Table(Table.from_tuple_likes([])) reports columns: [], and calling sort_values(by=["x"]) on it raises KeyError: 'x'. Building the frame from the port's schema instead, through pyarrow.Table.from_pylist([], schema=schema.as_arrow_schema()).to_pandas(), gives columns ['x', 'name'] with dtypes int32 and object, and the same sort succeeds with shape (0, 2).

Part of #8325: the export's verification runs each operator on an empty table too, and a Python operator's engine-side run cannot be compared until this is fixed. The bug itself is not about the export, and reaches Sort, the visualization operators and any user-written UDFTableOperator in an ordinary run.

Version/Branch

1.4.0-incubating-SNAPSHOT (main)

Commit Hash (Optional)

1fbd34627

Relevant log output
KeyError: 'x'
Dominant language
Scala
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3d 10h
Merged PRs (30d)
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