apache kafka系列之在zookeeper中存儲結構

1.topic註冊信息

/brokers/topics/[topic] :

存儲某個topic的partitions全部分配信息

Schema: {     "version": "版本編號目前固定爲數字1",     "partitions": {         "partitionId編號": [             同步副本組brokerId列表         ],         "partitionId編號": [             同步副本組brokerId列表         ],         .......     } } Example: { "version": 1, "partitions": { "0": [1, 2], "1": [2, 1], "2": [1, 2], } } 說明：紫紅色爲patitions編號，藍色爲同步副本組brokerId列表

2.partition狀態信息

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

/brokers/topics/[topic]/partitions/[partitionId]/state

Schema: { "controller_epoch": 表示kafka集羣中的中央控制器選舉次數, "leader": 表示該partition選舉leader的brokerId, "version": 版本編號默認爲1, "leader_epoch": 該partition leader選舉次數, "isr": [同步副本組brokerId列表] }   Example: { "controller_epoch": 1, "leader": 2, "version": 1, "leader_epoch": 0, "isr": [2, 1] }

3. Broker註冊信息

/brokers/ids/[0...N]                 

每一個broker的配置文件中都須要指定一個數字類型的id(全局不可重複),此節點爲臨時znode(EPHEMERAL)

Schema: { "jmx_port": jmx端口號, "timestamp": kafka broker初始啓動時的時間戳, "host": 主機名或ip地址, "version": 版本編號默認爲1, "port": kafka broker的服務端端口號,由server.properties中參數port肯定 }   Example: { "jmx_port": 6061, "timestamp":"1403061899859" "version": 1, "host": "192.168.1.148", "port": 9092 }

4. Controller epoch: 

/controller_epoch -> int (epoch)   

此值爲一個數字,kafka集羣中第一個broker第一次啓動時爲1，之後只要集羣中center controller中央控制器所在broker變動或掛掉，就會從新選舉新的center controller，每次center controller變動controller_epoch值就會 + 1; 

5. Controller註冊信息:

/controller -> int (broker id of the controller)  存儲center controller中央控制器所在kafka broker的信息

Schema: { "version": 版本編號默認爲1, "brokerid": kafka集羣中broker惟一編號, "timestamp": kafka broker中央控制器變動時的時間戳 }   Example: { "version": 1, "brokerid": 3, "timestamp": "1403061802981" }

Consumer and Consumer group概念: 

a.每一個consumer客戶端被建立時,會向zookeeper註冊本身的信息;
b.此做用主要是爲了"負載均衡".
c.同一個Consumer Group中的Consumers，Kafka將相應Topic中的每一個消息只發送給其中一個Consumer。
d.Consumer Group中的每一個Consumer讀取Topic的一個或多個Partitions，而且是惟一的Consumer；
e.一個Consumer group的多個consumer的全部線程依次有序地消費一個topic的全部partitions,若是Consumer group中全部consumer總線程大於partitions數量，則會出現空閒狀況;

舉例說明：

kafka集羣中建立一個topic爲report-log   4 partitions 索引編號爲0,1,2,3

假若有目前有三個消費者node：注意-->一個consumer中一個消費線程能夠消費一個或多個partition.

若是每一個consumer建立一個consumer thread線程,各個node消費狀況以下，node1消費索引編號爲0,1分區，node2費索引編號爲2,node3費索引編號爲3

若是每一個consumer建立2個consumer thread線程，各個node消費狀況以下(是從consumer node前後啓動狀態來肯定的)，node1消費索引編號爲0,1分區；node2費索引編號爲2,3；node3爲空閒狀態

總結 ：
從以上可知，Consumer Group中各個consumer是根據前後啓動的順序有序消費一個topic的全部partitions的。

若是Consumer Group中全部consumer的總線程數大於partitions數量，則可能consumer thread或consumer會出現空閒狀態。

Consumer均衡算法
當一個group中,有consumer加入或者離開時,會觸發partitions均衡.均衡的最終目的,是提高topic的併發消費能力.
1) 假如topic1,具備以下partitions: P0,P1,P2,P3
2) 加入group中,有以下consumer: C0,C1
3) 首先根據partition索引號對partitions排序: P0,P1,P2,P3
4) 根據(consumer.id + '-'+ thread序號)排序: C0,C1
5) 計算倍數: M = [P0,P1,P2,P3].size / [C0,C1].size,本例值M=2(向上取整)
6) 而後依次分配partitions: C0 = [P0,P1],C1=[P2,P3],即Ci = [P(i * M),P((i + 1) * M -1)]

6. Consumer註冊信息:

每一個consumer都有一個惟一的ID(consumerId能夠經過配置文件指定,也能夠由系統生成),此id用來標記消費者信息.

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

是一個臨時的znode,此節點的值爲請看consumerIdString產生規則,即表示此consumer目前所消費的topic + partitions列表.

consumerId產生規則：

   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;

Schema: { "version": 版本編號默認爲1, "subscription": { //訂閱topic列表 "topic名稱": consumer中topic消費者線程數 }, "pattern": "static", "timestamp": "consumer啓動時的時間戳" }   Example: { "version": 1, "subscription": { "open_platform_opt_push_plus1": 5 }, "pattern": "static", "timestamp": "1411294187842" }

7. Consumer owner:

/consumers/[groupId]/owners/[topic]/[partitionId] -> consumerIdString + threadId索引編號

當consumer啓動時,所觸發的操做:

a) 首先進行"Consumer Id註冊";

b) 而後在"Consumer id 註冊"節點下注冊一個watch用來監聽當前group中其餘consumer的"退出"和"加入";只要此znode path下節點列表變動,都會觸發此group下consumer的負載均衡.(好比一個consumer失效,那麼其餘consumer接管partitions).

c) 在"Broker id 註冊"節點下,註冊一個watch用來監聽broker的存活狀況;若是broker列表變動,將會觸發全部的groups下的consumer從新balance.

8. Consumer offset:

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

用來跟蹤每一個consumer目前所消費的partition中最大的offset

此znode爲持久節點,能夠看出offset跟group_id有關,以代表當消費者組(consumer group)中一個消費者失效,

從新觸發balance,其餘consumer能夠繼續消費.

9. Re-assign partitions

/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]         }      ]             }

 

10. Preferred replication election

/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                  }      ]             }

 

11. 刪除topics
/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"] }

Topic配置

/config/topics/[topic_name]

例子

{   "version": 1,   "config": {     "config.a": "x",     "config.b": "y",     ...    } }