Kafka学习之路 （五）Kafka在zookeeper中的存储

当kafka启动的时候，就会向zookeeper里面注册一些信息，这些数据也称为Kafka的元数据信息。

1、Kafka在zookeeper中存储结构图

2、分析

根目录下的结构

服务端开启的状况下，进入客户端的命令：{zookeeper目录}/bin/zkCli.sh

# {zookeeper目录}/bin/zkCli.sh
[zk: localhost:2181(CONNECTED) 1] ls /
[cluster, controller_epoch, controller, brokers, zookeeper, admin, isr_change_notification, consumers, log_dir_event_notification, latest_producer_id_block, config]

2.1　topic注册信息

/brokers/topics/[topic] :

存储某个topic的partitions全部分配信息

[zk: localhost:2181(CONNECTED) 1] get /brokers/topics/topic2

Schema:
{
    "version": "版本编号目前固定为数字1",
    "partitions": {
        "partitionId编号": [
            同步副本组brokerId列表
        ],
        "partitionId编号": [
            同步副本组brokerId列表
        ],
        .......
    }
}
Example:
{
"version": 1,
"partitions": {
"2": [1, 2, 3],
"1": [0, 1, 2],
"0": [3, 0, 1],
}
}

2.2　partition状态信息

/brokers/topics/[topic]/partitions/[0...N] 其中[0..N]表示partition索引号

[zk: localhost:2181(CONNECTED) 2] ls /brokers/topics/[topic]/partitions
[0, 1, 2]
[zk: localhost:2181(CONNECTED) 3] /brokers/topics/[topic]/partitions/[partitionId]/state

Schema:
{
"controller_epoch": 表示kafka集群中的中央控制器选举次数,
"leader": 表示该partition选举leader的brokerId,
"version": 版本编号默认为1,
"leader_epoch": 该partition leader选举次数,
"isr": [同步副本组brokerId列表]
}

Example:
{
"controller_epoch": 1,
"leader": 3,
"version": 1,
"leader_epoch": 0,
"isr": [3, 0, 1]
}

2.3　Broker注册信息

/brokers/ids/[0...N]

[zk: localhost:2181(CONNECTED) 4] ls /brokers/ids
[0, 1, 2, 3]
[zk: localhost:2181(CONNECTED) 5] get /brokers/ids/0

每一个broker的配置文件中都须要指定一个数字类型的id(全局不可重复),此节点为临时znode(EPHEMERAL)

Schema:
{
"jmx_port": jmx端口号,
"timestamp": kafka broker初始启动时的时间戳,
"host": 主机名或ip地址,
"version": 版本编号默认为1,
"port": kafka broker的服务端端口号,由server.properties中参数port肯定
}

Example:
{
"jmx_port": -1,
"timestamp":"1525741823119"
"version": 1,
"host": "hadoop1",
"port": 9092
}

2.4　Controller epoch

[zk: localhost:2181(CONNECTED) 6] get /controller_epoch
1

此值为一个数字,kafka集群中第一个broker第一次启动时为1，之后只要集群中center controller中央控制器所在broker变动或挂掉，就会从新选举新的center controller，每次center controller变动controller_epoch值就会 + 1;

2.5　Controller注册信息

存储center controller中央控制器所在kafka broker的信息

[zk: localhost:2181(CONNECTED) 7] get /controller

Schema:
{
"version": 版本编号默认为1,
"brokerid": kafka集群中broker惟一编号,
"timestamp": kafka broker中央控制器变动时的时间戳
}

Example:
{
"version": 1,
"brokerid": 0,
"timestamp": "1525741822769"
}

2.6　补充Consumer and Consumer group

① 每一个consumer客户端被建立时,会向zookeeper注册本身的信息;
② 此做用主要是为了"负载均衡"。
③ 同一个Consumer Group中的Consumers，Kafka将相应Topic中的每一个消息只发送给其中一个Consumer。
④ Consumer Group中的每一个Consumer读取Topic的一个或多个Partitions，而且是惟一的Consumer。
⑤ 一个Consumer group的多个consumer的全部线程依次有序地消费一个topic的全部partitions,若是Consumer group中全部consumer总线程大于partitions数量，则会出现空闲状况。

举例说明：

kafka集群中建立一个topic为report-log 4 partitions 索引编号为0,1,2,3

假若有目前有三个消费者node：注意 --> 一个consumer中一个消费线程能够消费一个或多个partition

若是每一个consumer建立一个consumer thread线程,各个node消费状况以下，node1消费索引编号为0,1分区，node2费索引编号为2,node3费索引编号为3

若是每一个consumer建立2个consumer thread线程，各个node消费状况以下(是从consumer node前后启动状态来肯定的)，node1消费索引编号为0,1分区；node2费索引编号为2,3；node3为空闲状态

总结：

从以上可知，Consumer Group中各个consumer是根据前后启动的顺序有序消费一个topic的全部partitions的。

若是Consumer Group中全部consumer的总线程数大于partitions数量，则可能consumer thread或consumer会出现空闲状态。

2.7　Consumer均衡算法

当一个group中,有consumer加入或者离开时,会触发partitions均衡.均衡的最终目的,是提高topic的并发消费能力。

1) 假如topic1,具备以下partitions: P0,P1,P2,P3
2) 加入group中,有以下consumer: C0,C1
3) 首先根据partition索引号对partitions排序: P0,P1,P2,P3
4) 根据(consumer.id + '-'+ thread序号)排序: C0,C1
5) 计算倍数: M = [P0,P1,P2,P3].size / [C0,C1].size,本例值M=2(向上取整)
6) 而后依次分配partitions: C0 = [P0,P1],C1=[P2,P3],即Ci = [P(i M),P((i + 1) M -1)]

2.8　Consumer注册信息

每一个consumer都有一个惟一的ID(consumerId能够经过配置文件指定,也能够由系统生成),此id用来标记消费者信息。

/consumers/[groupId]/ids/[consumerIdString]

是一个临时的znode,此节点的值为请看consumerIdString产生规则,即表示此consumer目前所消费的topic + partitions列表。

consumerId产生规则：

StringconsumerUuid = null;
    if(config.consumerId!=null && config.consumerId)
      consumerUuid = consumerId;
    else {
      String uuid = UUID.randomUUID()
      consumerUuid = "%s-%d-%s".format(
        InetAddress.getLocalHost.getHostName, System.currentTimeMillis,
        uuid.getMostSignificantBits().toHexString.substring(0,8));

     }
     String consumerIdString = config.groupId + "_" + consumerUuid;

[zk: localhost:2181(CONNECTED) 8] ls /consumers
[zk: localhost:2181(CONNECTED) 9] ls /consumers/console-consumer-2034/ids
[zk: localhost:2181(CONNECTED) 10] get /consumers/console-consumer-2034/ids/console-consumer-2034_kafka1-8454138431234-7a59ee48

Schema:
{
"version": 版本编号默认为1,
"subscription": { //订阅topic列表
"topic名称": consumer中topic消费者线程数
},
"pattern": "static",
"timestamp": "consumer启动时的时间戳"
}

Example:
{
"version": 1,
"subscription": {
"topic2": 1
},
"pattern": "white_list",
"timestamp": "1525747915336"
}

2.9　Consumer owner

/consumers/[groupId]/owners/[topic]/[partitionId] -> consumerIdString + threadId索引编号

a) 首先进行"Consumer Id注册"。
b) 而后在"Consumer id 注册"节点下注册一个watch用来监听当前group中其余consumer的"退出"和"加入";只要此znode path下节点列表变动,都会触发此group下consumer的负载均衡.(好比一个consumer失效,那么其余consumer接管partitions)。
c) 在"Broker id 注册"节点下,注册一个watch用来监听broker的存活状况;若是broker列表变动,将会触发全部的groups下的consumer从新balance。

[zk: localhost:2181(CONNECTED) 11] ls /consumers
[console-consumer-2034]
[zk: localhost:2181(CONNECTED) 12] ls /consumers/console-consumer-2034/owners
[topic2]
[zk: localhost:2181(CONNECTED) 13] ls /consumers/console-consumer-2034/owners/topic2
[0, 1, 2]
[zk: localhost:2181(CONNECTED) 14] get /consumers/console-consumer-2034/owners/topic2/0

2.10　Consumer offset

/consumers/[groupId]/offsets/[topic]/[partitionId] -> long (offset)

用来跟踪每一个consumer目前所消费的partition中最大的offset。

此znode为持久节点,能够看出offset跟group_id有关,以代表当消费者组(consumer group)中一个消费者失效，

从新触发balance,其余consumer能够继续消费。

[zk: localhost:2181(CONNECTED) 15] get /consumers/console-consumer-2034/offsets/topic2/0

2.11　Re-assign partitions

[zk: localhost:2181(CONNECTED) 16] get /admin/reassign_partitions

{
   "fields":[
      {
         "name":"version",
         "type":"int",
         "doc":"version id"
      },
      {
         "name":"partitions",
         "type":{
            "type":"array",
            "items":{
               "fields":[
                  {
                     "name":"topic",
                     "type":"string",
                     "doc":"topic of the partition to be reassigned"
                  },
                  {
                     "name":"partition",
                     "type":"int",
                     "doc":"the partition to be reassigned"
                  },
                  {
                     "name":"replicas",
                     "type":"array",
                     "items":"int",
                     "doc":"a list of replica ids"
                  }
               ],
            }
            "doc":"an array of partitions to be reassigned to new replicas"
         }
      }
   ]
}

Example:
{
  "version": 1,
  "partitions":
     [
        {
            "topic": "Foo",
            "partition": 1,
            "replicas": [0, 1, 3]
        }
     ]            
}

2.12　Preferred replication election

[zk: localhost:2181(CONNECTED) 17] get /admin/preferred_replica_election

{
   "fields":[
      {
         "name":"version",
         "type":"int",
         "doc":"version id"
      },
      {
         "name":"partitions",
         "type":{
            "type":"array",
            "items":{
               "fields":[
                  {
                     "name":"topic",
                     "type":"string",
                     "doc":"topic of the partition for which preferred replica election should be triggered"
                  },
                  {
                     "name":"partition",
                     "type":"int",
                     "doc":"the partition for which preferred replica election should be triggered"
                  }
               ],
            }
            "doc":"an array of partitions for which preferred replica election should be triggered"
         }
      }
   ]
}

例子:

{
  "version": 1,
  "partitions":
     [
        {
            "topic": "Foo",
            "partition": 1         
        },
        {
            "topic": "Bar",
            "partition": 0         
        }
     ]            
}

2.13　删除topics

[zk: localhost:2181(CONNECTED) 18] get /admin/delete_topics

Schema:
{ "fields":
    [ {"name": "version", "type": "int", "doc": "version id"},
      {"name": "topics",
       "type": { "type": "array", "items": "string", "doc": "an array of topics to be deleted"}
      } ]
}

例子:
{
  "version": 1,
  "topics": ["foo", "bar"]
}

2.14　Topic配置

/config/topics/[topic_name]

[zk: localhost:2181(CONNECTED) 19] get /config/topics/topic2