python kafka：如何使每个味精从一开始就按组只消耗一次

【问题标题】：python kafka: how to make each msg consumed only once by group from beginingpython kafka：如何使每个味精从一开始就按组只消耗一次
【发布时间】：2016-08-31 19:08:51
【问题描述】：

我在这里使用Kafka consumer（版本 1.3.1）。

我要实现的目标：

  • 有 10 个分区。每个分区都从偏移量 0 开始。

  • 有一组消费者（例如 1、2、3）。

  • 有时，一位消费者已关闭或已启动。

  • 因此，组成员可能会发生变化。但是我希望每个分区中的每条消息都应该被组消费一次（1 OR 2 OR 3）。

我的代码是：

consumer = KafkaConsumer('my_topic',
            bootstrap_servers=['ip:9092'],
            auto_offset_reset='earliest',
            max_partition_fetch_bytes=131072,
            group_id='writer.test')

以上配置够吗？欢迎任何cmets。谢谢

更新

我尝试了以下代码。每次在分区 760 中，每条消息可能被一组中的两个消费者消费两次。为什么？有什么问题吗？

def test():
    #PULL FROM KAFKA
    consumer = KafkaConsumer(
            'topic',
            bootstrap_servers=[ip],
            auto_offset_reset='latest',
            max_partition_fetch_bytes=131072,
            auto_commit_interval_ms=500,
            group_id='writer2.test')

    print consumer.poll()
    for i in range(10000):
        msg = next(consumer)
        if str(msg[1])=='670':
            print 'partition= %s, offset= %s' % (msg[1], msg[2])
    consumer.unsubscribe()


if __name__ == "__main__":
    for i in range(10):
        import time
        time.sleep(5)
        test()

输出 1：

{}
partition= 670, offset= 224
partition= 670, offset= 225
partition= 670, offset= 226
partition= 670, offset= 227
partition= 670, offset= 228
partition= 670, offset= 229
partition= 670, offset= 230
partition= 670, offset= 231
partition= 670, offset= 232
partition= 670, offset= 233
partition= 670, offset= 234
partition= 670, offset= 235
partition= 670, offset= 236
partition= 670, offset= 237
partition= 670, offset= 238
partition= 670, offset= 239
partition= 670, offset= 240
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259

在另一个窗口运行同一个文件，输出：

{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259
{}
partition= 670, offset= 241
partition= 670, offset= 242
partition= 670, offset= 243
partition= 670, offset= 244
partition= 670, offset= 245
partition= 670, offset= 246
partition= 670, offset= 247
partition= 670, offset= 248
partition= 670, offset= 249
partition= 670, offset= 250
partition= 670, offset= 251
partition= 670, offset= 252
partition= 670, offset= 253
partition= 670, offset= 254
partition= 670, offset= 255
partition= 670, offset= 256
partition= 670, offset= 257
partition= 670, offset= 258
partition= 670, offset= 259

【问题讨论】：

  • 您使用的是单代理还是多代理集群？
  • @MoinuddinQuadri 多代理集群。有什么区别吗？
  • 我相信你的问题是，你有多个消费者。并且您正在广播的数据被所有消费者接收。但是你希望它只被一个消费者消费。我说的对吗？
  • @MoinuddinQuadri 查看我的更新。谢谢
  • 之前我已经研究过了。我们面临的问题是早期版本的 Kafka 在消费者端维护提交状态（即偏移量的消耗）。并且库不提供任何消费者之间的交流方式。然而，在新版本的 Kafka（我猜是 Kafka 2.1 或 +，不确定版本）中，它由代理维护，因此不需要处理。只需验证一次，您就可以休息了。

标签： python apache-kafka kafka-consumer-api kafka-python


【解决方案1】：

如果您使用消费者组，Kafka 提供至少一次传递保证，因此，在消费者失败时重新分配这些消费者的分区，一些消息可能会被第二次传递。

如果您想确保没有消息被处理两次，您可以将模式切换为最多一次传递保证。但是，为此，您可能会丢失一些消息（即，从未处理过）以防失败。

要启用最多一次，您需要禁用自动提交，并在poll 之后直接手动提交，即在开始处理通过poll 收到的消息之前。

请参阅http://docs.confluent.io/3.0.0/clients/consumer.html#detailed-examples 了解更多详情（即使示例不在 Python 中，一般模式也是一样的）。

【讨论】：

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