Today, I’d like to share a simple but common scenario of MySQL-to-MySQL data synchronization and merging. This case reflects a problem I encountered in real work, and I hope it can spark discussion. I welcome more experienced peers to share insights and ideas. Version Requirement: Apache SeaTunnel → Apache SeaTunnel-2.3.9 Version Requirement: Apache SeaTunnel → Apache SeaTunnel-2.3.9 Version Requirement: Scenario Description In our business system, there are two MySQL source databases: source_asource_b source_a source_a source_b source_b Both databases contain a table with the same structure, but the data comes from different business lines. Data is generated simultaneously on both sides, which leads to primary key conflicts. primary key conflicts Our goal is to merge the tables from these two sources into a single target database (we call it C) for unified analysis and querying. C Challenges Faced Although the two source tables have the same structure, primary keys may conflict, which must be avoided.In the future, there may be differences in fields or new fields added.The synchronization process should be as real-time as possible, without generating duplicate data. Although the two source tables have the same structure, primary keys may conflict, which must be avoided. In the future, there may be differences in fields or new fields added. The synchronization process should be as real-time as possible, without generating duplicate data. Solution We implemented the synchronization and merging solution as follows: Create the target table in database C: The table structure needs to cover all fields from both source tables (currently identical, but may expand in the future).Add an extra field: data_source to indicate the data origin (source_a or source_b).Non-nullable fields must have default values. The table structure needs to cover all fields from both source tables (currently identical, but may expand in the future). Add an extra field: data_source to indicate the data origin (source_a or source_b). data_source source_a source_b Non-nullable fields must have default values. Set composite primary key and unique constraint: Use original primary key + data_source as a composite primary key to ensure no conflict arises from overlapping keys in the two sources. Use original primary key + data_source as a composite primary key to ensure no conflict arises from overlapping keys in the two sources. original primary key + data_source data_source Use two separate SeaTunnel processes for data synchronization: Use MySQL CDC connector to monitor source_a and source_b respectively.Add a data_source field to each record.Use JDBC Sink to write data into database C. Use MySQL CDC connector to monitor source_a and source_b respectively. MySQL CDC connector source_a source_b Add a data_source field to each record. data_source Use JDBC Sink to write data into database C. JDBC Sink Practical Demo Let’s get straight to the practical part. Since the basics of SeaTunnel have been covered in the previous article, we won’t repeat them here. Preparations Before Using MySQL CDC To use the mysql-cdc connector, there are two prerequisites: mysql-cdc The MySQL source must have Binlog enabled:binlog_format must be set to ROW.binlog_row_image must be set to FULL.Check current configuration: The MySQL source must have Binlog enabled: Binlog enabled binlog_format must be set to ROW. binlog_format ROW binlog_row_image must be set to FULL. binlog_row_image FULL Check current configuration: SHOW VARIABLES LIKE 'binlog_format';
SHOW VARIABLES LIKE 'binlog_row_image';

-- If not enabled, add the following to my.cnf:
[mysqld]
server-id = 1
log-bin = mysql-bin
binlog-format = ROW
binlog-row-image = FULL SHOW VARIABLES LIKE 'binlog_format';
SHOW VARIABLES LIKE 'binlog_row_image';

-- If not enabled, add the following to my.cnf:
[mysqld]
server-id = 1
log-bin = mysql-bin
binlog-format = ROW
binlog-row-image = FULL Detailed permission descriptions and setup can be found in the official documentation. It is recommended to review it. Prepare a user account with replication privileges: Prepare a user account with replication privileges: -- Create CDC user
CREATE USER 'cdc_user'@'%' IDENTIFIED BY 'your_password';

-- Grant necessary privileges
GRANT SELECT, RELOAD, SHOW DATABASES, REPLICATION SLAVE, REPLICATION CLIENT ON *.* TO 'cdc_user'@'%';
FLUSH PRIVILEGES; -- Create CDC user
CREATE USER 'cdc_user'@'%' IDENTIFIED BY 'your_password';

-- Grant necessary privileges
GRANT SELECT, RELOAD, SHOW DATABASES, REPLICATION SLAVE, REPLICATION CLIENT ON *.* TO 'cdc_user'@'%';
FLUSH PRIVILEGES; Preparing SeaTunnel Runtime Package and Plugins Option 1: Download official binary package Option 1: Download official binary package Option 1: Download official binary package Suitable when the server can access the internet and no custom plugins are needed. Download from the official Releases page.Manually add plugins and driver dependencies (e.g., mysql-cdc, jdbc).Plugin installation instructions can be found in the official documentation: Download from the official Releases page. official Releases page Manually add plugins and driver dependencies (e.g., mysql-cdc, jdbc). mysql-cdc jdbc Plugin installation instructions can be found in the official documentation: wget "https://archive.apache.org/dist/seatunnel/${version}/apache-seatunnel-${version}-bin.tar.gz"

# Keep needed plugins in config/plugin_config
bin/install-plugin.sh wget "https://archive.apache.org/dist/seatunnel/${version}/apache-seatunnel-${version}-bin.tar.gz"

# Keep needed plugins in config/plugin_config
bin/install-plugin.sh Option 2: Clone the source code from GitHub and build manually Option 2: Clone the source code from GitHub and build manually Option 2: Clone the source code from GitHub and build manually Suitable if you need special plugin support or want all plugins included by default. sh ./mvnw clean install -DskipTests -Dskip.spotless=true

# The generated package:
seatunnel-dist/target/apache-seatunnel-2.3.9-bin.tar.gz sh ./mvnw clean install -DskipTests -Dskip.spotless=true

# The generated package:
seatunnel-dist/target/apache-seatunnel-2.3.9-bin.tar.gz The manually built package already includes all plugins and dependencies; no extra steps are required. Plugins used in this case: Plugins used in this case: mysql-cdcjdbc mysql-cdc mysql-cdc jdbc jdbc Plugin documentation and driver dependencies are also available in the official docs. Overview of Apache SeaTunnel Deployment Methods SeaTunnel supports multiple deployment methods: Using the built-in engine (Zeta)Running as a Spark/Flink job Using the built-in engine (Zeta) Running as a Spark/Flink job Three modes for Zeta engine: ModeDescriptionUsage SuggestionLocal ModeRuns as a single local process, not maintainable, suitable for testingFor testingMixed ModeMaster and Worker are in the same process, prone to resource competitionNot recommendedSeparate ModeMaster and Worker are deployed separately, with independent resources and high stabilityRecommended ModeDescriptionUsage SuggestionLocal ModeRuns as a single local process, not maintainable, suitable for testingFor testingMixed ModeMaster and Worker are in the same process, prone to resource competitionNot recommendedSeparate ModeMaster and Worker are deployed separately, with independent resources and high stabilityRecommended ModeDescriptionUsage Suggestion ModeDescriptionUsage Suggestion Mode Description Usage Suggestion Local ModeRuns as a single local process, not maintainable, suitable for testingFor testingMixed ModeMaster and Worker are in the same process, prone to resource competitionNot recommendedSeparate ModeMaster and Worker are deployed separately, with independent resources and high stabilityRecommended Local ModeRuns as a single local process, not maintainable, suitable for testingFor testing Local Mode Runs as a single local process, not maintainable, suitable for testing For testing Mixed ModeMaster and Worker are in the same process, prone to resource competitionNot recommended Mixed Mode Master and Worker are in the same process, prone to resource competition Not recommended Separate ModeMaster and Worker are deployed separately, with independent resources and high stabilityRecommended Separate Mode Master and Worker are deployed separately, with independent resources and high stability Recommended Configuration File Structure Once the cluster is set up, we prepare configuration files. Generally, SeaTunnel configuration files can be divided into four parts: Env: Engine-related configurationSource: Source data reading configurationTransform: Data transformation (optional)Sink: Target database writing configuration Env: Engine-related configuration Env Source: Source data reading configuration Source Transform: Data transformation (optional) Transform Sink: Target database writing configuration Sink Env (Engine Configuration) parallelism: Task parallelism. Higher numbers speed up execution, but should match available resources.job.mode: Job execution mode. Since we use mysql-cdc, it must be set to Streaming.checkpoint.interval: Interval for checkpoints. Streaming mode defaults to 30 seconds, adjustable if needed. parallelism: Task parallelism. Higher numbers speed up execution, but should match available resources. parallelism job.mode: Job execution mode. Since we use mysql-cdc, it must be set to Streaming. job.mode mysql-cdc Streaming checkpoint.interval: Interval for checkpoints. Streaming mode defaults to 30 seconds, adjustable if needed. checkpoint.interval Source Configuration (MySQL CDC) For mysql-cdc, configure: mysql-cdc Connection info: database host, username, password, etc.Database/table selection: can specify via database-names and table-names or use regex for pattern matching.startup.mode: CDC startup mode, default is full snapshot then incremental, suitable for most sync scenarios.server-id: MySQL CDC reader ID. Optional but recommended to avoid conflicts with existing replica IDs.MySQL prerequisites: ensureBinlog is enabledbinlog-format is ROWbinlog-row-image is FULLAccount has privileges to read binlogs, replication, and query all tables. Connection info: database host, username, password, etc. Database/table selection: can specify via database-names and table-names or use regex for pattern matching. database-names table-names startup.mode: CDC startup mode, default is full snapshot then incremental, suitable for most sync scenarios. startup.mode full snapshot then incremental server-id: MySQL CDC reader ID. Optional but recommended to avoid conflicts with existing replica IDs. server-id MySQL prerequisites: ensure Binlog is enabled binlog-format is ROW binlog-format ROW binlog-row-image is FULL binlog-row-image FULL Account has privileges to read binlogs, replication, and query all tables. Transform Configuration (Optional) In this case, we add a field to each record indicating its data source, e.g., data_source with values source_a or source_b. data_source source_a source_b This transformation uses the SQL plugin to add a constant column with the source info. SQL plugin Each source table can have its own transformation rules.source_table is a reserved word indicating the previous processing table. Each source table can have its own transformation rules. source_table is a reserved word indicating the previous processing table. source_table Sink Configuration The JDBC Sink is configured with: JDBC Sink Target database address, driver, username, password, etc.Generate insert SQL based on target table structure.If fields/structure differ, custom SQL can be used to match the table. Target database address, driver, username, password, etc. Generate insert SQL based on target table structure. If fields/structure differ, custom SQL can be used to match the table. Summary After combining these configurations, we can synchronize multiple source databases (e.g., source_a and source_b) to the target database in real time. source_a source_b Additionally, the data is labeled with the source and written consistently. This approach supports complex data structures and flexible business scenarios—suitable for real production data integration cases. Sink Writing Optimization and Validation We can also optimize Sink write performance: Batch Writing Strategy Batch size and write interval: Data will be written when either condition is met. Batch size and write interval: Data will be written when either condition is met. Batch size write interval Key Configuration Parameters schema_save_mode: Strategy for saving schema. If it exists, ignore; if not, create automatically from previous output.data_save_mode: Data save strategy; here we use append mode.support_upsert_by_query_primary_key_exist: Enable upsert on primary key conflicts; this is enabled in this case.primary_keys: Specify primary keys for writing; must include the original table key and the data_sourceadded in the transform phase. schema_save_mode: Strategy for saving schema. If it exists, ignore; if not, create automatically from previous output. schema_save_mode data_save_mode: Data save strategy; here we use append mode. data_save_mode append support_upsert_by_query_primary_key_exist: Enable upsert on primary key conflicts; this is enabled in this case. support_upsert_by_query_primary_key_exist primary_keys: Specify primary keys for writing; must include the original table key and the data_sourceadded in the transform phase. primary_keys data_source Submitting Tasks ./seatunnel.sh --config ../config/demo/collect_a.config -e cluster --cluster sz-seatunnel --name collect_a --async
./seatunnel.sh --config ../config/demo/collect_b.config -e cluster --cluster sz-seatunnel --name collect_b --async

# Explanation:
# --config: configuration file
# -e: execution mode (cluster/local)
# --cluster: cluster name
# --name: job name
# --async: run in background ./seatunnel.sh --config ../config/demo/collect_a.config -e cluster --cluster sz-seatunnel --name collect_a --async
./seatunnel.sh --config ../config/demo/collect_b.config -e cluster --cluster sz-seatunnel --name collect_b --async

# Explanation:
# --config: configuration file
# -e: execution mode (cluster/local)
# --cluster: cluster name
# --name: job name
# --async: run in background Validation of Actual Run Now that the configuration is complete, let’s see the results: a and b tables contain data; c is empty.Run the a sync process. a and b tables contain data; c is empty. a b c Run the a sync process. a Check c table: data from a is written, data_source = source_a. Check c table: data from a is written, data_source = source_a. c a data_source source_a Run the b sync process. Run the b sync process. b Check c table: data from b is written, data_source = source_b. Check c table: data from b is written, data_source = source_b. c b data_source source_b Modify some data in a. Modify some data in a. a With batch write strategy, wait 2 seconds and check c.Corresponding data is updated as expected. With batch write strategy, wait 2 seconds and check c. c Corresponding data is updated as expected. This completes the entire data synchronization and merging process. 🙏 I hope this case provides some inspiration. You’re welcome to share more of your Apache SeaTunnel experiences so we can learn together!

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Synchronizing Data from MySQL to PostgreSQL Using Apache SeaTunnel

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