alibaba canal原理简介及客户端代码示例Demo-java,架构-星河码客

什么是canal

官方的解释是：基于数据库增量日志解析，提供增量数据订阅&消费，目前主要支持了mysql。按我的理解就是获取并解析mysql binlog的一个工具。详情可参考canal

当前的 canal 支持源端 MySQL 版本包括 5.1.x , 5.5.x , 5.6.x , 5.7.x , 8.0.x

背景

早期阿里巴巴因为杭州和美国双机房部署，存在跨机房同步的业务需求，实现方式主要是基于业务 trigger 获取增量变更。从 2010 年开始，业务逐步尝试数据库日志解析获取增量变更进行同步，由此衍生出了大量的数据库增量订阅和消费业务。

原理

canal 工作原理

canal 模拟 MySQL slave 的交互协议，伪装自己为 MySQL slave ，向 MySQL master 发送dump 协议
MySQL master 收到 dump 请求，开始推送 binary log 给 slave (即 canal )
canal 解析 binary log 对象(原始为 byte 流)

简单说就是伪装为mysal 从服务器，接受数据修改bin log 然后解析，提供给canal client 消费同步

关于mysql 主备搭建请参考 https://www.cnblogs.com/itliyh/p/13803693.html

canal client示例代码

java.net.InetSocketAddress;
import java.util.List;


import com.alibaba.otter.canal.client.CanalConnectors;
import com.alibaba.otter.canal.client.CanalConnector;
import com.alibaba.otter.canal.common.utils.AddressUtils;
import com.alibaba.otter.canal.protocol.Message;
import com.alibaba.otter.canal.protocol.CanalEntry.Column;
import com.alibaba.otter.canal.protocol.CanalEntry.Entry;
import com.alibaba.otter.canal.protocol.CanalEntry.EntryType;
import com.alibaba.otter.canal.protocol.CanalEntry.EventType;
import com.alibaba.otter.canal.protocol.CanalEntry.RowChange;
import com.alibaba.otter.canal.protocol.CanalEntry.RowData;


public class SimpleCanalClientExample {


    public static void main(String args[]) {
        // 创建链接
        CanalConnector connector = CanalConnectors.newSingleConnector(new InetSocketAddress(AddressUtils.getHostIp(),
                11111), "example", "", ""); // port是默认的端口，如果server的端口你自己修改过，这里要改成对应的
        int batchSize = 512;
        int emptyCount = 0;
        try {
            connector.connect();
            connector.subscribe(".*\\..*"); //订阅当前链接下所有数据库下所有表的变更。如果你只想看某个表也可以改成你自己的形式，如test\\..*,test\\.mytable
            connector.rollback();
            int totalEmptyCount = 120;  // 做个限制，防止无限循环，你也可以自己改大
            while (emptyCount < totalEmptyCount) {
                Message message = connector.getWithoutAck(batchSize); // 获取指定数量的数据，getWithoutAck在canal文档中有详细介绍
                System.out.println(message.toString());
                long batchId = message.getId();
                int size = message.getEntries().size();
                if (batchId == -1 || size == 0) {
                    emptyCount++;
                    System.out.println("empty count : " + emptyCount);
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                    }
                } else {
                    emptyCount = 0;
                    // System.out.printf("message[batchId=%s,size=%s] \n", batchId, size);
                    printEntry(message.getEntries());
                }

                connector.ack(batchId); // 提交确认
                // connector.rollback(batchId); // 处理失败, 回滚数据。rollback需要你自己加个判断
            }

            System.out.println("empty too many times, exit");
        } finally {
            connector.disconnect();
        }
    }

    private static void printEntry(List<Entry> entrys) {
        for (Entry entry : entrys) {
            if (entry.getEntryType() == EntryType.TRANSACTIONBEGIN || entry.getEntryType() == EntryType.TRANSACTIONEND) {
                continue;
            }

            RowChange rowChage = null;
            try {
                rowChage = RowChange.parseFrom(entry.getStoreValue());
            } catch (Exception e) {
                throw new RuntimeException("ERROR ## parser of eromanga-event has an error , data:" + entry.toString(),
                        e);
            }

            EventType eventType = rowChage.getEventType();
            System.out.println(String.format("================> binlog[%s:%s] , name[%s,%s] , eventType : %s",
                    entry.getHeader().getLogfileName(), entry.getHeader().getLogfileOffset(),
                    entry.getHeader().getSchemaName(), entry.getHeader().getTableName(),
                    eventType));

            for (RowData rowData : rowChage.getRowDatasList()) {
                if (eventType == EventType.DELETE) {
                    printColumn(rowData.getBeforeColumnsList());
                } else if (eventType == EventType.INSERT) {
                    printColumn(rowData.getAfterColumnsList());
                } else {
                    System.out.println("-------> before");
                    printColumn(rowData.getBeforeColumnsList());
                    System.out.println("-------> after");
                    printColumn(rowData.getAfterColumnsList());
                }
            }
        }
    }

    private static void printColumn(List<Column> columns) {
        for (Column column : columns) {
            System.out.println(column.getName() + " : " + column.getValue() + "    update=" + column.getUpdated());
        }

具体的消息格式：

Message[id=3,entries=[header {
  version: 1
  logfileName: "mysql-bin.000002"
  logfileOffset: 685
  serverId: 1
  serverenCode: "UTF-8"
  executeTime: 1545980851000
  sourceType: MYSQL
  schemaName: ""
  tableName: ""
  eventLength: 72
  props {
    key: "curtGtid"
    value: "ba229943-d845-11e8-9fcc-0492264bb587:3"
  }
  props {
    key: "curtGtidSn"
    value: "null"
  }
  props {
    key: "curtGtidLct"
    value: "null"
  }
  gtid: "ba229943-d845-11e8-9fcc-0492264bb587:1-3"
}
entryType: TRANSACTIONBEGIN
storeValue: " \004"
, header {
  version: 1
  logfileName: "mysql-bin.000002"
  logfileOffset: 807
  serverId: 1
  serverenCode: "UTF-8"
  executeTime: 1545980851000
  sourceType: MYSQL
  schemaName: "test"
  tableName: "test"
  eventLength: 42
  eventType: INSERT
  props {
    key: "curtGtid"
    value: "ba229943-d845-11e8-9fcc-0492264bb587:3"
  }
  props {
    key: "curtGtidSn"
    value: "null"
  }
  props {
    key: "curtGtidLct"
    value: "null"
  }
  props {
    key: "rowsCount"
    value: "1"
  }
  gtid: "ba229943-d845-11e8-9fcc-0492264bb587:1-3"
}
entryType: ROWDATA
storeValue: "\bF\020\001P\000b?\022\032\b\000\020\004\032\002id \001(\0010\000B\0015R\aint(11)\022!\b\001\020\f\032\004name \000(\0010\000B\0015R\fvarchar(255)"
, header {
  version: 1
  logfileName: "mysql-bin.000002"
  logfileOffset: 849
  serverId: 1
  serverenCode: "UTF-8"
  executeTime: 1545980851000
  sourceType: MYSQL
  schemaName: ""
  tableName: ""
  eventLength: 31
  props {
    key: "curtGtid"
    value: "ba229943-d845-11e8-9fcc-0492264bb587:3"
  }
  props {
    key: "curtGtidSn"
    value: "null"
  }
  props {
    key: "curtGtidLct"
    value: "null"
  }
  gtid: "ba229943-d845-11e8-9fcc-0492264bb587:1-3"
}
entryType: TRANSACTIONEND
storeValue: "\022\00235"
],raw=true,rawEntries=[]]

更多语言客户端示例，请参考：

canal java 客户端: https://github.com/alibaba/canal/wiki/ClientExample
canal c# 客户端: https://github.com/dotnetcore/CanalSharp
canal go客户端: https://github.com/CanalClient/canal-go
canal php客户端: https://github.com/xingwenge/canal-php
canal Python客户端：https://github.com/haozi3156666/canal-python
canal Rust客户端：https://github.com/laohanlinux/canal-rs