apache/flink · error · IOException

Can't deserialize Debezium Avro message.

Error message

Can't deserialize Debezium Avro message.

What it means

This is the outer safety net of DebeziumAvroDeserializationSchema.deserialize(): every Throwable thrown while decoding an Avro record or converting before/after images (NPEs, Avro decoder errors, converter type mismatches, and the wrapped replica-identity IllegalStateExceptions) is caught and re-thrown as IOException("Can't deserialize Debezium Avro message."). The original cause is always attached; the real diagnosis lives in the cause chain, not this message.

Source

Thrown at flink-formats/flink-avro-confluent-registry/src/main/java/org/apache/flink/formats/avro/registry/confluent/debezium/DebeziumAvroDeserializationSchema.java:168

                after.setRowKind(RowKind.UPDATE_AFTER);
                out.collect(before);
                out.collect(after);
            } else if (OP_DELETE.equals(op)) {
                if (before == null) {
                    throw new IllegalStateException(
                            String.format(REPLICA_IDENTITY_EXCEPTION, "DELETE"));
                }
                before.setRowKind(RowKind.DELETE);
                out.collect(before);
            } else {
                throw new IOException(
                        format(
                                "Unknown \"op\" value \"%s\". The Debezium Avro message is '%s'",
                                op, new String(message)));
            }
        } catch (Throwable t) {
            // a big try catch to protect the processing.
            throw new IOException("Can't deserialize Debezium Avro message.", t);
        }
    }

    @Override
    public boolean isEndOfStream(RowData nextElement) {
        return false;
    }

    @Override
    public TypeInformation<RowData> getProducedType() {
        return producedTypeInfo;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Read the full cause chain (getCause()) of the IOException — the actionable error is the nested exception, not this wrapper.
2. If the cause is the replica-identity IllegalStateException, follow the fix for error 1320 (ALTER TABLE ... REPLICA IDENTITY FULL).
3. If the cause is an Avro/schema error, verify the Flink table schema matches the Debezium 'before'/'after' record schema and that the registry serves the writer schema.
4. If the cause is connectivity, verify 'schema.registry.url' is reachable from TaskManagers and retry from the last checkpoint.

catch (IOException e) { Throwable root = e; while (root.getCause()!=null) root = root.getCause(); // switch on root: IllegalStateException->replica identity, AvroTypeException->schema mismatch, RestServiceException->registry connectivity }

When it happens

Trigger: Any decode/conversion failure inside deserialize(): registry lookup failures for the writer schema ID, Avro datum resolution errors, RowData converter type mismatches between the registered Avro schema and the declared Flink table schema, or the before==null replica-identity errors (errors 1320/1321 nested as causes).

Common situations: Schema evolution in the registry producing an incompatible reader schema; Flink table columns reordered or retyped relative to the Debezium schema; transient schema-registry connectivity blips; the underlying causes described for the REPLICA_IDENTITY and unknown-op errors.

Related errors

• Could not serialize row '%s'.
• 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/293349d6f3f9006d. Report an issue: GitHub.