Canal Format

Changelog-Data-Capture Format Format: Serialization Schema Format: Deserialization Schema

Canal is a CDC (Changelog Data Capture) tool that can stream changes in real-time from MySQL into other systems. Canal provides a unified format schema for changelog and supports to serialize messages using JSON and protobuf (protobuf is the default format for Canal).

Nexus supports to interpret Canal JSON messages as INSERT/UPDATE/DELETE messages into Nexus 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.

Nexus also supports to encode the INSERT/UPDATE/DELETE messages in Nexus as Canal JSON messages, and emit to storage like Kafka. However, currently Nexus can’t combine UPDATE_BEFORE and UPDATE_AFTER into a single UPDATE message. Therefore, Nexus encodes UPDATE_BEFORE and UPDATE_AFTER as DELETE and INSERT Canal messages.

Format Options

Option	Default	Required	Description
format	(none)	yes	Specify what format to use, here should be 'canal_json'.
canal_json.ignore-parse-errors	false	no	Skip fields and rows with parse errors instead of failing. Fields are set to null in case of errors.
canal_json.database.include	(none)	no	An optional regular expression to only read the specific databases changelog rows by regular matching the "database" meta field in the Canal record. The pattern string is compatible with Java's Pattern.
canal_json.table.include	(none)	no	An optional regular expression to only read the specific tables changelog rows by regular matching the "table" meta field in the Canal record. The pattern string is compatible with Java's Pattern.

How to use

Kafka Uses Example​

Canal provides a unified format for changelog, here is a simple example for an update operation captured from a MySQL products table:

{
  "data": [
    {
      "id": "111",
      "name": "scooter",
      "description": "Big 2-wheel scooter",
      "weight": "5.18"
    }
  ],
  "database": "inventory",
  "es": 1589373560000,
  "id": 9,
  "isDdl": false,
  "mysqlType": {
    "id": "INTEGER",
    "name": "VARCHAR(255)",
    "description": "VARCHAR(512)",
    "weight": "FLOAT"
  },
  "old": [
    {
      "weight": "5.15"
    }
  ],
  "pkNames": [
    "id"
  ],
  "sql": "",
  "sqlType": {
    "id": 4,
    "name": 12,
    "description": 12,
    "weight": 7
  },
  "table": "products",
  "ts": 1589373560798,
  "type": "UPDATE"
}

Note: please refer to Canal documentation about the meaning of each fields.

The MySQL products table has 4 columns (id, name, description and weight). The above JSON message is an update change event on the products table where the weight value of the row with id = 111 is changed from 5.15 to 5.18. Assuming the messages have been synchronized to Kafka topic products_binlog, then we can use the following Nexus to consume this topic and interpret the change events.

env {
    parallelism = 1
    job.mode = "BATCH"
}

source {
  Kafka {
    bootstrap.servers = "kafkaCluster:9092"
    topic = "products_binlog"
    result_table_name = "kafka_name"
    start_mode = earliest
    schema = {
      fields {
           id = "int"
           name = "string"
           description = "string"
           weight = "string"
      }
    },
    format = canal_json
  }

}

transform {
}

sink {
  Kafka {
    bootstrap.servers = "localhost:9092"
    topic = "consume-binlog"
    format = canal_json
  }
}