apache/flink · error · RuntimeException

Could not serialize row '%s'.

Error message

Could not serialize row '%s'.

What it means

Outer catch in CsvRowDataSerializationSchema.serialize(): any Throwable thrown while converting the RowData into the CSV ObjectNode or writing it with Jackson is re-thrown as RuntimeException("Could not serialize row '%s'."). The failing row is included and the real cause (usually a converter type error) is attached.

Source

Thrown at flink-formats/flink-csv/src/main/java/org/apache/flink/formats/csv/CsvRowDataSerializationSchema.java:183

                                JsonNodeFeature.STRIP_TRAILING_BIGDECIMAL_ZEROES, false);
                        return csvMapper;
                    });
        }
    }

    @Override
    public byte[] serialize(RowData row) {
        if (root == null) {
            root = csvMapper.createObjectNode();
            converterContext =
                    new RowDataToCsvConverters.RowDataToCsvConverter
                            .RowDataToCsvFormatConverterContext(csvMapper, root);
        }
        try {
            runtimeConverter.convert(row, converterContext);
            return objectWriter.writeValueAsBytes(root);
        } catch (Throwable t) {
            throw new RuntimeException(String.format("Could not serialize row '%s'.", row), t);
        }
    }

    @Override
    public boolean equals(Object o) {
        if (o == null || o.getClass() != this.getClass()) {
            return false;
        }
        if (this == o) {
            return true;
        }
        final CsvRowDataSerializationSchema that = (CsvRowDataSerializationSchema) o;
        final CsvSchema otherSchema = that.csvSchema;

        return rowType.equals(that.rowType)
                && csvSchema.getColumnSeparator() == otherSchema.getColumnSeparator()
                && Arrays.equals(csvSchema.getLineSeparator(), otherSchema.getLineSeparator())
                && csvSchema

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Read the chained cause to identify which field/converter failed; the row dump shows the offending values.
2. Align the emitting side's RowType with the sink table schema exactly (types and nullability).
3. Test serialization in a unit test: new CsvRowDataSerializationSchema(rowType, options).serialize(row) to reproduce cheaply.
4. If the cause is an unsupported type, project/cast the column to a CSV-supported type (e.g. MAP to STRING) before the sink.

// Reproduce serialization cheaply before deploying:
SerializationSchema<RowData> ser = new CsvRowDataSerializationSchema(rowType, config);
for (RowData sample : representativeRows) { ser.serialize(sample); } // throws here, not in prod

catch (RuntimeException e) { send the row (rendered in e.getMessage()) to a dead-letter sink; rethrow only for systemic causes (schema/registry) }

When it happens

Trigger: RowData values incompatible with the declared CSV schema: wrong physical type in a GenericRowData, unsupported nested types, nulls rendered into positions the CsvSchema cannot format, or date/time strings that Jackson's CSV generator rejects.

Common situations: Custom sources emitting GenericRowData with mismatched internal representations (e.g. byte[] where STRING expected); schema drift between the producing job and the CSV sink DDL; timestamps with precision the CSV schema cannot render.

Related errors

• Can't deserialize Debezium Avro message.
• Could not serialize row '%s'.
• Could not serialize row '%s'.
• Could not serialize row '%s'.
• Cannot deserialize and unwrap accumulators properly.

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/e101c6de051ea206. Report an issue: GitHub.