public static ControlRecordType parse(ByteBuffer key) {
        return fromTypeId(parseTypeId(key));
    }
Control records specify a schema for the record key which includes a version and type:

Key => Version Type
  Version => Int16
  Type => Int16

In the future, the version can be bumped to indicate a new schema, but it must be backwards compatible
with the current schema. In general, this means we can add new fields, but we cannot remove old ones.

Note that control records are not considered for compaction by the log cleaner.

The schema for the value field is left to the control record type to specify.
clients/src/main/java/org/apache/kafka/common/record/ControlRecordType.java