Maxwell

Function

Flink supports to interpret Maxwell JSON messages as INSERT/UPDATE/DELETE messages into Flink SQL system. This is useful in many cases to leverage this feature,

such as:

Synchronizing incremental data from databases to other systems
Auditing logs
Real-time materialized views on databases
Temporal join changing history of a database table and so on

Flink also supports to encode the INSERT/UPDATE/DELETE messages in Flink SQL as Maxwell JSON messages, and emit to external systems like Kafka. However, currently Flink cannot combine UPDATE_BEFORE and UPDATE_AFTER into a single UPDATE message. Therefore, Flink encodes UPDATE_BEFORE and UDPATE_AFTER as DELETE and INSERT Maxwell messages.

Parameters

**Table 1**
Parameter	Mandatory	Default Value	Type	Description
format	Yes	None	String	Format to be used. Set this parameter to maxwell-json.
maxwell-json.ignore-parse-errors	No	false	Boolean	Whether fields and rows with parse errors will be skipped or failed. Fields are set to null in case of errors.
maxwell-json.timestamp-format.standard	No	'SQL'	String	Input and output timestamp formats. Currently supported values are SQL and ISO-8601: SQL will parse input timestamp in "yyyy-MM-dd HH:mm:ss.s{precision}" format, for example, 2020-12-30 12:13:14.123 and output timestamp in the same format. ISO-8601 will parse input timestamp in "yyyy-MM-ddTHH:mm:ss.s{precision}" format, for example 2020-12-30T12:13:14.123 and output timestamp in the same format.
maxwell-json.map-null-key.mode	No	'FAIL'	String	Handling mode when serializing null keys for map data. Currently supported values are 'FAIL', 'DROP' and 'LITERAL': FAIL will throw exception when encountering map with null key. DROP will drop null key entries for map data. LITERAL will replace null key with string literal. The string literal is defined by maxwell-json.map-null-key.literal option.
maxwell-json.map-null-key.literal	No	'null'	String	String literal to replace null key when maxwell-json.map-null-key.mode is LITERAL.

Supported Connectors

Kafka

Example

Use Kafka to send data and output the data to print.

Create a datasource connection for the communication with the VPC and subnet where Kafka locates and bind the connection to the queue. Set a security group and inbound rule to allow access of the queue and test the connectivity of the queue using the Kafka IP address. For example, locate a general-purpose queue where the job runs and choose More > Test Address Connectivity in the Operation column. If the connection is successful, the datasource is bound to the queue. Otherwise, the binding fails.

Create a Flink OpenSource SQL job and select Flink 1.12. Copy the following statement and submit the job:

create table kafkaSource(
  id bigint,
  name string,
  description string,
  weight DECIMAL(10, 2)  
  ) with (
    'connector' = 'kafka',
    'topic' = '<yourTopic>',
    'properties.group.id' = '<yourGroupId>',
    'properties.bootstrap.servers' = '<yourKafkaAddress1>:<yourKafkaPort>,<yourKafkaAddress2>:<yourKafkaPort>',
    'scan.startup.mode' = 'latest-offset',
    'format' = 'maxwell-json'
);
create table printSink(
  id bigint,
  name string,
  description string,
  weight DECIMAL(10, 2)
   ) with (
     'connector' = 'print'
   );
insert into printSink select * from kafkaSource;

Insert the following data to the corresponding topic in Kafka:

{
   "database":"test",
   "table":"e",
   "type":"insert",
   "ts":1477053217,
   "xid":23396,
   "commit":true,
   "position":"master.000006:800911",
   "server_id":23042,
   "thread_id":108,
   "primary_key": [1, "2016-10-21 05:33:37.523000"],
   "primary_key_columns": ["id", "c"],
   "data":{
     "id":111,
     "name":"scooter",
     "description":"Big 2-wheel scooter",
     "weight":5.15
   },
   "old":{
     "weight":5.18
   }
}

View the output through either of the following methods:
- Method 1: Locate the job and click More > FlinkUI. Choose Task Managers > Stdout.
- Method 2: If you allow DLI to save job logs in OBS, view the output in the taskmanager.out file.
```
+I(111,scooter,Big 2-wheel scooter,5.15)
```