pathwaycom/pathway · error · ValueError

'schema_registry_settings' is only meaningful for the 'json'

Error message

'schema_registry_settings' is only meaningful for the 'json' format, but {format!r} was specified. The Confluent Schema Registry currently encodes JSON payloads only; remove 'schema_registry_settings' or use format='json'.

What it means

Raised by MessageQueueOutputFormat.build when schema_registry_settings is combined with a format other than 'json'. The Confluent Schema Registry integration in this connector only encodes JSON payloads (JSON Schema), so registry settings with 'dsv', 'raw', or 'plaintext' would be silently unused; Pathway raises instead.

Source

Thrown at python/pathway/io/_utils.py:478

                "'subject' was provided without 'schema_registry_settings'. "
                "The 'subject' parameter only has an effect when a schema "
                "registry is configured; either pass 'schema_registry_settings' "
                "or remove 'subject'."
            )
        if schema_registry_settings is not None and subject is None:
            raise ValueError(
                "'schema_registry_settings' was provided without 'subject'. "
                "When a schema registry is configured, 'subject' must also be "
                "set so the formatter knows which subject to encode under."
            )
        if subject is not None and not subject:
            raise ValueError(
                "'subject' must be a non-empty string; got an empty string. "
                "Schema Registry subjects identify a named schema version, "
                "and an empty subject is never a valid registry entry."
            )
        if schema_registry_settings is not None and format != "json":
            raise ValueError(
                f"'schema_registry_settings' is only meaningful for the 'json' "
                f"format, but {format!r} was specified. The Confluent Schema "
                "Registry currently encodes JSON payloads only; remove "
                "'schema_registry_settings' or use format='json'."
            )

        key_field_index = None
        header_fields: dict[str, int] = {}
        extracted_field_indices: dict[str, int] = {}
        columns_to_extract: list[ColumnReference] = []

        if topic_name is not None:
            topic_name_index = cls.add_column_reference_to_extract(
                topic_name, columns_to_extract, extracted_field_indices
            )
            if topic_name._column.dtype not in (dt.STR, dt.ANY):
                raise ValueError(
                    "The topic name column must have a string type, however "

View on GitHub (pinned to fa2f74a464)

Solutions

1. Use format='json' if you need Schema Registry encoding.
2. Or remove schema_registry_settings (and subject) when writing dsv/raw/plaintext.

Example fix

# before
pw.io.kafka.write(t, ..., format='raw',
    schema_registry_settings=settings, subject='s')

# after
pw.io.kafka.write(t, ..., format='json',
    schema_registry_settings=settings, subject='s')

if schema_registry_settings is not None:
    assert format == 'json', "Schema Registry output encoding requires format='json'"

try:
    pw.io.kafka.write(t, ..., format=format, schema_registry_settings=settings, subject=s)
except ValueError as e:
    if "only meaningful for the 'json' format" in str(e):
        pw.io.kafka.write(t, ..., format=format)  # registry not applicable; drop it
    else:
        raise

When it happens

Trigger: pw.io.kafka.write(table, ..., format='dsv', schema_registry_settings=settings, subject=...); switching an output format from json to raw while keeping registry settings; assuming Avro registry support (format='avro' style usage) that this writer does not have.

Common situations: Teams expecting Avro-style schema-registry encoding; refactoring output format while leaving registry options in the call.

Related errors

• Unsupported argument for {data_format!r} format: 'value'
• 'subject' was provided without 'schema_registry_settings'. T
• 'schema_registry_settings' was provided without 'subject'. W
• 'subject' must be a non-empty string; got an empty string. S
• 'value' and format='{format}' cannot be set at the same time

AI-assisted analysis of pathwaycom/pathway@fa2f74a464 (2026-08-15). Data as JSON: /api/errors/4cdfef63f9bce14a. Report an issue: GitHub.