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。
一、Kafka在zookeeper中存储结构图
二、分析
根目录下的结构
服务端开启的情况下，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所有分配信息
[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每个broker的配置文件中都需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确定
}
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，以后只要集群中center controller中央控制器所在broker变更或挂掉，就会重新选举新的center controller，每次center controller变更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唯一编号,
"timestamp": kafka broker中央控制器变更时的时间戳
}
Example:
{
"version": 1,
"brokerid": 0,
"timestamp": "1525741822769"
}2.6 补充Consumer and Consumer group
① 每个consumer客户端被创建时,会向zookeeper注册自己的信息;
② 此作用主要是为了"负载均衡"。
③ 同一个Consumer Group中的Consumers，Kafka将相应Topic中的每个消息只发送给其中一个Consumer。
④ Consumer Group中的每个Consumer读取Topic的一个或多个Partitions，并且是唯一的Consumer。
⑤ 一个Consumer group的多个consumer的所有线程依次有序地消费一个topic的所有partitions,如果Consumer group中所有consumer总线程大于partitions数量，则会出现空闲情况。
举例说明：
kafka集群中创建一个topic为report-log 4 partitions 索引编号为0,1,2,3
假如有目前有三个消费者node：注意 --> 一个consumer中一个消费线程可以消费一个或多个partition
如果每个consumer创建一个consumer thread线程,各个node消费情况如下，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
如果每个consumer创建2个consumer thread线程，各个node消费情况如下(是从consumer node先后启动状态来确定的)，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是根据先后启动的顺序有序消费一个topic的所有partitions的。
如果Consumer Group中所有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,是提升topic的并发消费能力。
1) 假如topic1,具有如下partitions: P0,P1,P2,P3
2) 加入group中,有如下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) 然后依次分配partitions: C0 = [P0,P1],C1=[P2,P3],即Ci = [P(i M),P((i + 1) M -1)]
2.8 Consumer注册信息
每个consumer都有一个唯一的ID(consumerId可以通过配置文件指定,也可以由系统生成),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) 然后在"Consumer id 注册"节点下注册一个watch用来监听当前group中其他consumer的"退出"和"加入";只要此znode path下节点列表变更,都会触发此group下consumer的负载均衡.(比如一个consumer失效,那么其他consumer接管partitions)。
c) 在"Broker id 注册"节点下,注册一个watch用来监听broker的存活情况;如果broker列表变更,将会触发所有的groups下的consumer重新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)
用来跟踪每个consumer目前所消费的partition中最大的offset。
此znode为持久节点,可以看出offset跟group_id有关,以表明当消费者组(consumer group)中一个消费者失效，
重新触发balance,其他consumer可以继续消费。
[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