Streaming ELT from MySQL to Doris #

This tutorial is to show how to quickly build a Streaming ELT job from MySQL to Doris using Flink CDC, including the feature of sync all table of one database, schema change evolution and sync sharding tables into one table.
All exercises in this tutorial are performed in the Flink CDC CLI, and the entire process uses standard SQL syntax, without a single line of Java/Scala code or IDE installation.

Preparation #

Prepare a Linux or MacOS computer with Docker installed.

Prepare Flink Standalone cluster #

Download Flink 1.18.0 ，unzip and get flink-1.18.0 directory.
Use the following command to navigate to the Flink directory and set FLINK_HOME to the directory where flink-1.18.0 is located.
```
cd flink-1.18.0
```
Enable checkpointing by appending the following parameters to the conf/flink-conf.yaml configuration file to perform a checkpoint every 3 seconds.
```
execution.checkpointing.interval: 3000
```
Start the Flink cluster using the following command.
```
./bin/start-cluster.sh
```

If successfully started, you can access the Flink Web UI at http://localhost:8081/, as shown below.

Executing start-cluster.sh multiple times can start multiple TaskManagers.

Prepare docker compose #

The following tutorial will prepare the required components using docker-compose.

Host Machine Configuration
Since Doris requires memory mapping support for operation, execute the following command on the host machine:
```
sysctl -w vm.max_map_count=2000000
```

Due to the different ways of implementing containers internally on MacOS, it may not be possible to directly modify the value of max_map_count on the host during deployment. You need to create the following containers first:

docker run -it --privileged --pid=host --name=change_count debian nsenter -t 1 -m -u -n -i sh

The container was created successfully executing the following command:

sysctl -w vm.max_map_count=2000000

Then exit exits and creates the Doris Docker cluster.

Start docker compose Create a docker-compose.yml file using the content provided below:

version: '2.1'
services:
  doris:
    image: yagagagaga/doris-standalone
    ports:
      - "8030:8030"
      - "8040:8040"
      - "9030:9030"
  mysql:
    image: debezium/example-mysql:1.1
    ports:
      - "3306:3306"
    environment:
      - MYSQL_ROOT_PASSWORD=123456
      - MYSQL_USER=mysqluser
      - MYSQL_PASSWORD=mysqlpw

The Docker Compose should include the following services (containers):

MySQL: include a database named app_db
Doris: to store tables from MySQL

To start all containers, run the following command in the directory that contains the docker-compose.yml file.

docker-compose up -d

This command automatically starts all the containers defined in the Docker Compose configuration in a detached mode. Run docker ps to check whether these containers are running properly. You can also visit http://localhost:8030/ to check whether Doris is running.

Prepare records for MySQL #

Enter MySQL container

docker-compose exec mysql mysql -uroot -p123456

create app_db database and orders,products,shipments tables, then insert records

-- create database
CREATE DATABASE app_db;

USE app_db;

-- create orders table
CREATE TABLE `orders` (
`id` INT NOT NULL,
`price` DECIMAL(10,2) NOT NULL,
PRIMARY KEY (`id`)
);

-- insert records
INSERT INTO `orders` (`id`, `price`) VALUES (1, 4.00);
INSERT INTO `orders` (`id`, `price`) VALUES (2, 100.00);

-- create shipments table
CREATE TABLE `shipments` (
`id` INT NOT NULL,
`city` VARCHAR(255) NOT NULL,
PRIMARY KEY (`id`)
);

-- insert records
INSERT INTO `shipments` (`id`, `city`) VALUES (1, 'beijing');
INSERT INTO `shipments` (`id`, `city`) VALUES (2, 'xian');

-- create products table
CREATE TABLE `products` (
`id` INT NOT NULL,
`product` VARCHAR(255) NOT NULL,
PRIMARY KEY (`id`)
);

-- insert records
INSERT INTO `products` (`id`, `product`) VALUES (1, 'Beer');
INSERT INTO `products` (`id`, `product`) VALUES (2, 'Cap');
INSERT INTO `products` (`id`, `product`) VALUES (3, 'Peanut');

Create database in Doris #

Doris connector currently does not support automatic database creation and needs to first create a database corresponding to the write table.

Enter Doris Web UI。
http://localhost:8030/
The default username is root, and the default password is empty.
Create app_db database through Web UI.
```
create database app_db;
```

Submit job with Flink CDC CLI #

Download the binary compressed packages listed below and extract them to the directory flink cdc-3.1.0'：
flink-cdc-3.1.0-bin.tar.gz flink-cdc-3.1.0 directory will contain four directory: bin, lib, log, and conf.
Download the connector package listed below and move it to the lib directory
Download links are available only for stable releases, SNAPSHOT dependencies need to be built based on master or release branches by yourself. Please note that you need to move the jar to the lib directory of Flink CDC Home, not to the lib directory of Flink Home.
- MySQL pipeline connector 3.1.0
- Apache Doris pipeline connector 3.1.0
You also need to place MySQL connector into Flink lib folder or pass it with --jar argument, since they’re no longer packaged with CDC connectors:
- MySQL Connector Java

Write task configuration yaml file Here is an example file for synchronizing the entire database mysql-to-doris.yaml：

################################################################################
# Description: Sync MySQL all tables to Doris
################################################################################
source:
  type: mysql
  hostname: localhost
  port: 3306
  username: root
  password: 123456
  tables: app_db.\.*
  server-id: 5400-5404
  server-time-zone: UTC

sink:
  type: doris
  fenodes: 127.0.0.1:8030
  username: root
  password: ""
  table.create.properties.light_schema_change: true
  table.create.properties.replication_num: 1

pipeline:
  name: Sync MySQL Database to Doris
  parallelism: 2

Notice that:
tables: app_db.\.* in source synchronize all tables in app_db through Regular Matching.
table.create.properties.replication_num in sink is because there is only one Doris BE node in the Docker image.

Finally, submit job to Flink Standalone cluster using Cli.
```
bash bin/flink-cdc.sh mysql-to-doris.yaml
```

After successful submission, the return information is as follows：

Pipeline has been submitted to cluster.
Job ID: ae30f4580f1918bebf16752d4963dc54
Job Description: Sync MySQL Database to Doris

We can find a job named Sync MySQL Database to Doris is running through Flink Web UI.

We can find that tables are created and inserted through Doris Web UI.

Synchronize Schema and Data changes #

Enter MySQL container

docker-compose exec mysql mysql -uroot -p123456

Then, modify schema and record in MySQL, and the tables of Doris will change the same in real time：

insert one record in orders from MySQL:

INSERT INTO app_db.orders (id, price) VALUES (3, 100.00);

add one column in orders from MySQL:

ALTER TABLE app_db.orders ADD amount varchar(100) NULL;

update one record in orders from MySQL:

UPDATE app_db.orders SET price=100.00, amount=100.00 WHERE id=1;

delete one record in orders from MySQL:
```
DELETE FROM app_db.orders WHERE id=2;
```

Refresh the Doris Web UI every time you execute a step, and you can see that the orders table displayed in Doris will be updated in real-time, like the following：

Similarly, by modifying the ‘shipments’ and’ products’ tables, you can also see the results of synchronized changes in real-time in Doris.

Route the changes #

Flink CDC provides the configuration to route the table structure/data of the source table to other table names.
With this ability, we can achieve functions such as table name, database name replacement, and whole database synchronization. Here is an example file for using route feature:

################################################################################
# Description: Sync MySQL all tables to Doris
################################################################################
source:
   type: mysql
   hostname: localhost
   port: 3306
   username: root
   password: 123456
   tables: app_db.\.*
   server-id: 5400-5404
   server-time-zone: UTC

sink:
   type: doris
   fenodes: 127.0.0.1:8030
   benodes: 127.0.0.1:8040
   username: root
   password: ""
   table.create.properties.light_schema_change: true
   table.create.properties.replication_num: 1

route:
   - source-table: app_db.orders
     sink-table: ods_db.ods_orders
   - source-table: app_db.shipments
     sink-table: ods_db.ods_shipments
   - source-table: app_db.products
     sink-table: ods_db.ods_products

pipeline:
   name: Sync MySQL Database to Doris
   parallelism: 2

Using the upper route configuration, we can synchronize the table schema and data of app_db.orders to ods_db.ods_orders, thus achieving the function of database migration.
Specifically, source-table support regular expression matching with multiple tables to synchronize sharding databases and tables. like the following：

route:
  - source-table: app_db.order\.*
    sink-table: ods_db.ods_orders

In this way, we can synchronize sharding tables like app_db.order01、app_db.order02、app_db.order03 into one ods_db.ods_orders tables.
Warning that there is currently no support for scenarios where the same primary key data exists in multiple tables, which will be supported in future versions.

Clean up #

After finishing the tutorial, run the following command to stop all containers in the directory of docker-compose.yml:

docker-compose down

Run the following command to stop the Flink cluster in the directory of Flink flink-1.18.0:

./bin/stop-cluster.sh