apache/flink · error · RuntimeException

Could not serialize row '%s'.

Error message

Could not serialize row '%s'.

What it means

Outer catch in DebeziumAvroSerializationSchema.serialize(): any Throwable raised while building the Debezium envelope GenericRecord or running the Avro serializer is re-thrown as RuntimeException("Could not serialize row '%s'."). The offending RowData is rendered into the message and the root cause is attached; diagnose via the cause, not the wrapper text.

Source

Thrown at flink-formats/flink-avro-confluent-registry/src/main/java/org/apache/flink/formats/avro/registry/confluent/debezium/DebeziumAvroSerializationSchema.java:129

                case UPDATE_AFTER:
                    outputReuse.setField(0, null);
                    outputReuse.setField(1, rowData);
                    outputReuse.setField(2, OP_INSERT);
                    return avroSerializer.serialize(outputReuse);
                case UPDATE_BEFORE:
                case DELETE:
                    outputReuse.setField(0, rowData);
                    outputReuse.setField(1, null);
                    outputReuse.setField(2, OP_DELETE);
                    return avroSerializer.serialize(outputReuse);
                default:
                    throw new UnsupportedOperationException(
                            format(
                                    "Unsupported operation '%s' for row kind.",
                                    rowData.getRowKind()));
            }
        } catch (Throwable t) {
            throw new RuntimeException(format("Could not serialize row '%s'.", rowData), t);
        }
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        DebeziumAvroSerializationSchema that = (DebeziumAvroSerializationSchema) o;
        return Objects.equals(avroSerializer, that.avroSerializer);
    }

    @Override
    public int hashCode() {
        return Objects.hash(avroSerializer);

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Inspect getCause() — fix whichever nested exception (UnsupportedOperationException, AvroTypeException, RestServiceException) is the real failure.
2. If the cause is the RowKind error, normalize kinds as per error 1325.
3. Verify the registry URL/credentials from TaskManagers: curl http://<registry>/subjects and confirm the subject is writable.
4. Reconcile table DDL with the target Avro schema (types and nullability of before/after).

catch (RuntimeException e) { Throwable root = deepest(e); if (root instanceof RestServiceException) retry/alert registry; else if (root instanceof UnsupportedOperationException) fix row kind; else surface row from message to DLQ; }

When it happens

Trigger: Type mismatches between the RowData and the Avro schema used by avroSerializer (e.g. string vs bytes), nulls written into non-nullable envelope fields, Avro registry client failures during schema registration, or the unsupported-RowKind UnsupportedOperationException (error 1325) bubbling up as the cause.

Common situations: DDL columns whose types drift from the registered subject schema; registry auth (basic/bearer) misconfigured so schema registration fails on first serialize; nulls in key columns.

Related errors

• Can't deserialize Debezium Avro message.
• Unknown "op" value "%s". The Debezium Avro message is '%s'
• Unsupported operation '%s' for row kind.
• Could not serialize row '%s'.
• Could not instantiate org.apache.flink.formats.avro.utils.Av

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/b41ba14b325f8943. Report an issue: GitHub.