【es】设置副本分片

1.设置副本分片

1.搜索引擎的模块 
数据采集模块，文本分析模块，索引存储模块，搜索模块。
索引存储模块使用倒排索引存储模块把写入的数据组织成倒排索引的结构，
还管理着数据的存储方式，路由方式，事务日志，索引状态。

2.主节点 
每个集群有且只有一个主节点，主节点是整个集群的管理者，它负责维护整个集群的元数据，并在节点数目
发生变化时及时更新集群的状态然后将状态发布给集群的其他节点。
主节点还负责索引分片的分配。

3.主节点的选举 
如果超过30s主节点的状态没有发布成功，则主节点失败，主候选节点需要选举新的主节点。
如果某个节点的最终确认响应超过90s没有发送到主节点，则主节点认为该节点掉线，
将其从集群列表中删除。

4.分片分配 
节点数变化或副本数变化，就会发送分片的重分配。

创建索引并设置分片
curl -X PUT localhost:9200/iot_004 -u elastic:elastic  -H "Content-Type: application/json" -d '
{
"settings":{
"number_of_shards":"3",
"number_of_replicas":"1"
}
}'
{"acknowledged":true,"shards_acknowledged":true,"index":"iot_004"}


查看索引的分片 
curl -X GET localhost:9200/_cat/shards/iot_004?v -u elastic:elastic  
[root@host-172-21-251-180 config]# curl -X GET localhost:9200/_cat/shards/iot_004?v -u elastic:elastic  
index   shard prirep state   docs store ip             node
iot_004 2     p      STARTED    0  226b localhost node-1
iot_004 2     r      STARTED    0  226b 192.168.1.188 node-2
iot_004 1     r      STARTED    0  226b localhost node-1
iot_004 1     p      STARTED    0  226b 192.168.1.188 node-2
iot_004 0     p      STARTED    0  226b localhost node-1
iot_004 0     r      STARTED    0  226b 192.168.1.188 node-2

--查看索引的分布 

检查 R0 的分配是否可以分配到当前节点。
curl -X GET localhost:9200/_cluster/allocation/explain -u elastic:elastic  -H "Content-Type: application/json" -d '
{
"index":"iot_004",
"shard":0,
"primary":false
}'

{
    "index":"iot_004",
    "shard":0,
    "primary":false,
    "current_state":"started",
    "current_node":{
        "id":"xT-aakS2RficXV5PI2fU9Q",
        "name":"node-2",
        "transport_address":"192.168.1.188:9300",
        "attributes":{
            "ml.machine_memory":"4129558528",
            "ml.max_open_jobs":"512",
            "xpack.installed":"true",
            "ml.max_jvm_size":"2067791872",
            "transform.node":"true"
        },
        "weight_ranking":1
    },
    "can_remain_on_current_node":"yes",
    "can_rebalance_cluster":"yes",
    "can_rebalance_to_other_node":"no",
    "rebalance_explanation":"cannot rebalance as no target node exists that can both allocate this shard and improve the cluster balance",
    "node_allocation_decisions":[
        {
            "node_id":"ziwZn3mQQ4-LH-6vLuYMUw",
            "node_name":"node-1",
            "transport_address":"localhost:9300",
            "node_attributes":{
                "xpack.installed":"true",
                "transform.node":"true"
            },
            "node_decision":"no",
            "weight_ranking":1,
            "deciders":[
                {
                    "decider":"same_shard",
                    "decision":"NO",
                    "explanation":"a copy of this shard is already allocated to this node [[iot_004][0], node[ziwZn3mQQ4-LH-6vLuYMUw], [P], s[STARTED], a[id=b18r-ftATWSPX8-7bBUGOw]]"
                }
            ]
        }
    ]
}

对于一个总分片数为N的索引而言，当集群节点的数据达到N以后，继续添加新节点无法
提升该索引的读写性能。