apache/flink · error · IOException

Unknown "type" value "%s". The Maxwell JSON message is '%s'

Error message

Unknown "type" value "%s". The Maxwell JSON message is '%s'

What it means

While parsing a Maxwell JSON message, the 'type' field was not one of 'insert', 'update', or 'delete' (OP_INSERT/OP_UPDATE/OP_DELETE). Because Maxwell messages can also be DDL/transaction/heartbeat events that have no row image, the deserializer refuses unknown types; with 'maxwell-json.ignore-parse-errors' = false (default) it throws IOException, otherwise it logs at debug and skips.

Source

Thrown at flink-formats/flink-json/src/main/java/org/apache/flink/formats/json/maxwell/MaxwellJsonDeserializationSchema.java:175

                    if (before.isNullAt(f) && oldField.findValue(fieldNames.get(f)) == null) {
                        // not null fields in "old" (before) means the fields are changed
                        // null/empty fields in "old" (before) means the fields are not changed
                        // so we just copy the not changed fields into before
                        before.setField(f, after.getField(f));
                    }
                }
                before.setRowKind(RowKind.UPDATE_BEFORE);
                after.setRowKind(RowKind.UPDATE_AFTER);
                genericRowDataList.add(handleRow(row, before));
                genericRowDataList.add(handleRow(row, after));
            } else if (OP_DELETE.equals(type)) {
                // "data" field is a row, contains deleted rows
                GenericRowData delete = (GenericRowData) row.getRow(0, fieldCount);
                delete.setRowKind(RowKind.DELETE);
                genericRowDataList.add(handleRow(row, delete));
            } else {
                if (!ignoreParseErrors) {
                    throw new IOException(
                            format(
                                    "Unknown \"type\" value \"%s\". The Maxwell JSON message is '%s'",
                                    type, new String(message)));
                }
                if (LOG.isDebugEnabled()) {
                    LOG.debug(
                            "Unknown \"type\" value '{}'. The Maxwell JSON message is '{}'.",
                            type,
                            new String(message));
                }
            }
        } catch (Throwable t) {
            // a big try catch to protect the processing.
            if (!ignoreParseErrors) {
                throw new IOException(
                        format("Corrupt Maxwell JSON message '%s'.", new String(message)), t);
            }
            if (LOG.isDebugEnabled()) {

View on GitHub (pinned to 2f3c205e92)

Solutions

  1. Set 'maxwell-json.ignore-parse-errors' = true on the source table to skip non-row events.
  2. Filter the upstream topic (Maxwell binlog filter / Kafka routing) so only row-change events reach the Flink source.
  3. Verify the message really is Maxwell-format (check the 'type' field values present on the topic with a console consumer).

Example fix

-- before
'format' = 'maxwell-json'
-- after
'format' = 'maxwell-json',
'maxwell-json.ignore-parse-errors' = 'true'
Defensive patterns

Strategy: try-catch

Validate before calling

// Pre-check the type field when tolerating non-row Maxwell events
com.fasterxml.jackson.databind.JsonNode n = MAPPER.readTree(message);
String type = n.path("type").asText("");
if (!"insert".equals(type) && !"update".equals(type) && !"delete".equals(type)) {
    return; // skip DDL/heartbeat/bootstrap events
}

Try / catch

try { schema.deserialize(message, collector); } catch (IOException e) { if (!ignoreParseErrors) throw e; /* else record and continue */ }

Prevention

When it happens

Trigger: A Maxwell 'bootstrap-insert', DDL, or position/heartbeat message arriving on the topic consumed by a maxwell-json table source; a hand-crafted message with a missing/mistyped 'type'; Maxwell version emitting new event types.

Common situations: Consuming a Maxwell topic that also carries DDL or bootstrap events; schema evolution events after ALTER TABLE; test data with a wrong 'type' value.

Related errors

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/ba1617fd2725c82c. Report an issue: GitHub.