聊聊rocketmq-mysql的BinlogPositionManager

• BinlogPositionManager提供了initBeginPosition、getBinlogFilename、getPosition方法；其中initBeginPosition方法根据config.startType的类型来执行不同逻辑，DEFAULT的是执行initPositionDefault，NEW_EVENT是执行initPositionFromBinlogTail，LAST_PROCESSED是执行initPositionFromMqTail，SPECIFIED是设置指定的binlogFilename及nextPosition

initPositionDefault

rocketmq-externals/rocketmq-mysql/src/main/java/org/apache/rocketmq/mysql/position/BinlogPositionManager.java

public class BinlogPositionManager {

	//......

    private void initPositionDefault() throws Exception {

        try {
            initPositionFromMqTail();
        } catch (Exception e) {
            logger.error("Init position from mq error.", e);
        }

        if (binlogFilename == null || nextPosition == null) {
            initPositionFromBinlogTail();
        }

    }

    //......

}

• initPositionDefault执行的是initPositionFromMqTail方法，在binlogFilename或者nextPosition为null时还会执行initPositionFromBinlogTail

initPositionFromBinlogTail

rocketmq-externals/rocketmq-mysql/src/main/java/org/apache/rocketmq/mysql/position/BinlogPositionManager.java

public class BinlogPositionManager {

	//......

    private void initPositionFromBinlogTail() throws SQLException {
        String sql = "SHOW MASTER STATUS";

        Connection conn = null;
        ResultSet rs = null;

        try {
            Connection connection = dataSource.getConnection();
            rs = connection.createStatement().executeQuery(sql);

            while (rs.next()) {
                binlogFilename = rs.getString("File");
                nextPosition = rs.getLong("Position");
            }

        } finally {

            if (conn != null) {
                conn.close();
            }
            if (rs != null) {
                rs.close();
            }
        }

    }

    //......

}

• initPositionFromBinlogTail方法通过SHOW MASTER STATUS来获取最新的binlogFilename及nextPosition

initPositionFromMqTail

rocketmq-externals/rocketmq-mysql/src/main/java/org/apache/rocketmq/mysql/position/BinlogPositionManager.java

public class BinlogPositionManager {

	//......

    private void initPositionFromMqTail() throws Exception {
        DefaultMQPullConsumer consumer = new DefaultMQPullConsumer("BINLOG_CONSUMER_GROUP");
        consumer.setNamesrvAddr(config.mqNamesrvAddr);
        consumer.setMessageModel(MessageModel.valueOf("BROADCASTING"));
        consumer.start();

        Set<MessageQueue> queues = consumer.fetchSubscribeMessageQueues(config.mqTopic);
        MessageQueue queue = queues.iterator().next();

        if (queue != null) {
            Long offset = consumer.maxOffset(queue);
            if (offset > 0)
                offset--;

            PullResult pullResult = consumer.pull(queue, "*", offset, 100);

            if (pullResult.getPullStatus() == PullStatus.FOUND) {
                MessageExt msg = pullResult.getMsgFoundList().get(0);
                String json = new String(msg.getBody(), "UTF-8");

                JSONObject js = JSON.parseObject(json);
                binlogFilename = (String) js.get("binlogFilename");
                nextPosition = js.getLong("nextPosition");
            }
        }

    }

    //......

}

• initPositionFromMqTail方法创建DefaultMQPullConsumer，然后从指定的topic拉取MessageQueue，然后通过consumer.maxOffset(queue)获取offset，再执行pull，找到第一个msg，然后设置binlogFilename及nextPosition

小结

BinlogPositionManager提供了initBeginPosition、getBinlogFilename、getPosition方法；其中initBeginPosition方法根据config.startType的类型来执行不同逻辑，DEFAULT的是执行initPositionDefault，NEW_EVENT是执行initPositionFromBinlogTail，LAST_PROCESSED是执行initPositionFromMqTail，SPECIFIED是设置指定的binlogFilename及nextPosition

聊聊rocketmq-mysql的BinlogPositionManager

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