Kafka學習之路 （五）Kafka在zookeeper中的儲存
目錄
正文
一、Kafka在zookeeper中儲存結構圖
二、分析
2.1 topic註冊資訊
/brokers/topics/[topic] :
儲存某個topic的partitions所有分配資訊
[zk: localhost:2181(CONNECTED) 1] get /brokers/topics/topic2
Schema:
{
"version": "版本編號目前固定為數字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": {
"2": [1, 2, 3],
"1": [0, 1, 2],
"0": [3, 0, 1],
}
}
2.2 partition狀態資訊
/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叢集中的中央控制器選舉次數,
"leader": 表示該partition選舉leader的brokerId,
"version": 版本編號預設為1,
"leader_epoch": 該partition leader選舉次數,
"isr": [同步副本組brokerId列表]
}
Example:
{
"controller_epoch": 1,
"leader": 3,
"version": 1,
"leader_epoch": 0,
"isr": [3, 0, 1]
}
2.3 Broker註冊資訊
/brokers/ids/[0...N]
每個broker的配置檔案中都需要指定一個數字型別的id(全域性不可重複),此節點為臨時znode(EPHEMERAL)
Schema:
{
"jmx_port": jmx埠號,
"timestamp": kafka broker初始啟動時的時間戳,
"host": 主機名或ip地址,
"version": 版本編號預設為1,
"port": kafka broker的服務端埠號,由server.properties中引數port確定
}
Example:
{
"jmx_port": -1,
"timestamp":"1525741823119"
"version": 1,
"host": "hadoop1",
"port": 9092
}
2.4 Controller epoch
/controller_epoch --> int (epoch)
此值為一個數字,kafka叢集中第一個broker第一次啟動時為1，以後只要叢集中center controller中央控制器所在broker變更或掛掉，就會重新選舉新的center controller，每次center controller變更controller_epoch值就會 + 1;
2.5 Controller註冊資訊
/controller -> int (broker id of the controller) 儲存center controller中央控制器所在kafka broker的資訊
Schema:
{
"version": 版本編號預設為1,
"brokerid": kafka叢集中broker唯一編號,
"timestamp": kafka broker中央控制器變更時的時間戳
}
Example:
{
"version": 1,
"brokerid": 0,
"timestamp": "1525741822769"
}
2.6 補充Consumer and Consumer group
a.每個consumer客戶端被建立時,會向zookeeper註冊自己的資訊;b.此作用主要是為了"負載均衡".c.同一個Consumer Group中的Consumers，Kafka將相應Topic中的每個訊息只發送給其中一個Consumer。d.Consumer Group中的每個Consumer讀取Topic的一個或多個Partitions，並且是唯一的Consumer；e.一個Consumer group的多個consumer的所有執行緒依次有序地消費一個topic的所有partitions,如果Consumer group中所有consumer匯流排程大於partitions數量，則會出現空閒情況;
舉例說明：
kafka叢集中建立一個topic為report-log 4 partitions 索引編號為0,1,2,3
假如有目前有三個消費者node：注意-->一個consumer中一個消費執行緒可以消費一個或多個partition.
如果每個consumer建立一個consumer thread執行緒,各個node消費情況如下，node1消費索引編號為0,1分割槽，node2費索引編號為2,node3費索引編號為3
如果每個consumer建立2個consumer thread執行緒，各個node消費情況如下(是從consumer node先後啟動狀態來確定的)，node1消費索引編號為0,1分割槽；node2費索引編號為2,3；node3為空閒狀態
總結：從以上可知，Consumer Group中各個consumer是根據先後啟動的順序有序消費一個topic的所有partitions的。
如果Consumer Group中所有consumer的匯流排程數大於partitions數量，則可能consumer thread或consumer會出現空閒狀態。
2.7 Consumer均衡演算法
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,是提升topic的併發消費能力.1) 假如topic1,具有如下partitions: P0,P1,P2,P32) 加入group中,有如下consumer: C0,C13) 首先根據partition索引號對partitions排序: P0,P1,P2,P34) 根據(consumer.id + '-'+ thread序號)排序: C0,C15) 計算倍數: M = [P0,P1,P2,P3].size / [C0,C1].size,本例值M=2(向上取整)6) 然後依次分配partitions: C0 = [P0,P1],C1=[P2,P3],即Ci = [P(i * M),P((i + 1) * M -1)]
2.8 Consumer註冊資訊
每個consumer都有一個唯一的ID(consumerId可以通過配置檔案指定,也可以由系統生成),此id用來標記消費者資訊.
/consumers/[groupId]/ids/[consumerIdString]
是一個臨時的znode,此節點的值為請看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;
[zk: localhost:2181(CONNECTED) 11] get /consumers/console-consumer-2304/ids/console-consumer-2304_hadoop2-1525747915241-6b48ff32
Schema:
{
"version": 版本編號預設為1,
"subscription": { //訂閱topic列表
"topic名稱": consumer中topic消費者執行緒數
},
"pattern": "static",
"timestamp": "consumer啟動時的時間戳"
}
Example:
{
"version": 1,
"subscription": {
"topic2": 1
},
"pattern": "white_list",
"timestamp": "1525747915336"
}
2.9 Consumer owner
/consumers/[groupId]/owners/[topic]/[partitionId] -> consumerIdString + threadId索引編號
a) 首先進行"Consumer Id註冊";
b) 然後在"Consumer id 註冊"節點下注冊一個watch用來監聽當前group中其他consumer的"退出"和"加入";只要此znode path下節點列表變更,都會觸發此group下consumer的負載均衡.(比如一個consumer失效,那麼其他consumer接管partitions).
c) 在"Broker id 註冊"節點下,註冊一個watch用來監聽broker的存活情況;如果broker列表變更,將會觸發所有的groups下的consumer重新balance.
2.10 Consumer offset
/consumers/[groupId]/offsets/[topic]/[partitionId] -> long (offset)
用來跟蹤每個consumer目前所消費的partition中最大的offset
此znode為持久節點,可以看出offset跟group_id有關,以表明當消費者組(consumer group)中一個消費者失效,
重新觸發balance,其他consumer可以繼續消費.
2.11 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]
}
]
}
2.12 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
}
]
}
2.13 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"]
}
2.14 Topic配置
/config/topics/[topic_name]
