ES 學習之indices APIs

1.關閉萬用字元，_all等操作

在index api 中可以使用_all或者逗號操作符，或者是萬用字元*，但是這些操作可能會導致誤操作，所有我們可以通過在配置檔案中配置如下屬性，這樣api中將不能使用像_all這樣的操作

action.destructive_requires_name=true

2.判斷index是已經存在

可以通過api的方式判斷一個index是否存在，如果index存在將會api呼叫將會返回200，如果不存在將會返回404，但是如果有別名和你查詢的名稱相同的時候，也會返回200，所以說這個api判斷是index或者是別名是否存在。遺憾的是我在elasticsearch-head中呼叫這個api的時候，一直提示正在請求…，沒有任何結果

HEAD /index_name

3.關閉/開啟index

索引可以被關閉/開啟， 一個關閉的索引的在叢集中基本不需要什麼開銷，除了維護其元資料需要的開銷，關閉的index後不能進行讀寫操作;這個API可以同時開啟或者是關閉多個index，但是預設情況下， 如果遇到index不存在，將會丟擲異常，我們可以通過在配置檔案中配置ignore_unavailable=true方式忽略這樣的問題，下邊是開啟、關閉api樣例：

POST /my_index/_close
POST /my_index/_open

ignore_unavailable=true

關閉index可能會消耗大量的磁碟空間，同時引發一下別的問題，elasticsearch官方描述是如下：

​ Closed indices consume a significant amount of disk-space which can cause problems in managed environments. Closing indices can be disabled via the cluster settings API by setting cluster.indices.close.enable to false. The default is true.

可以通過通過配置cluster.indices.close.enable=false的方式是index不可被關閉

cluster.indices.close.enable=false

4.等待分片操作

Because opening an index allocates its shards, the wait_for_active_shards setting on index creation applies to the index opening action as well. The default value for the wait_for_active_shards setting on the open index API is 0, which means that the command won’t wait for the shards to be allocated.

5.壓縮index（shrink index）

我們知道一個index的shards是不可以調整的， 但是我們可以通過shrink index api將一個index壓縮到一個新的index中， 但是這個api有很多要求：

• the target index must not exist
• The index must have more primary shards than the target index.
• The number of primary shards in the target index must be a factor of the number of primary shards in the source index. The source index must have more primary shards than the target index.
• The index must not contain more than 2,147,483,519 documents in total across all shards that will be shrunk into a single shard on the target index as this is the maximum number of docs that can fit into a single shard.
• The node handling the shrink process must have sufficient free disk space to accommodate a second copy of the existing index.

然後我們看看壓縮操作過程

• First, it creates a new target index with the same definition as the source index, but with a smaller number of primary shards.
• Then it hard-links segments from the source index into the target index. (If the file system doesn’t support hard-linking, then all segments are copied into the new index, which is a much more time consuming process.)
• Finally, it recovers the target index as though it were a closed index which had just been re-opened.

要執行要是， 源index必須是隻讀的，而且健康值是green

In order to shrink an index, the index must be marked as read-only, and a (primary or replica) copy of every shard in the index must be relocated to the same node and have health green.

執行樣例：

POST my_source_index/_shrink/my_target_index
{
  "settings": {
    "index.number_of_replicas": 1,
    "index.number_of_shards": 1, 
    "index.codec": "best_compression" 
  },
  "aliases": {
    "my_search_indices": {}
  }
}

6.rollover index(翻新index)

這個API可以從一個別名對應的index中翻新出一個新的index， 當你認為原來的index太舊或者是資料量太大時。這個api需要接收一個別名，還有一些判斷條件，而且這個別名必須只對應一個index，當滿足這些判斷條件的時候， 新的index在執行這個API會被建立

PUT /logs-000001 
{
  "aliases": {
    "logs_write": {}
  }
}

# Add > 1000 documents to logs-000001

如果沒有自己定義新index的名稱， elasticsearch會給你定義一個
POST /logs_write/_rollover 
{
  "conditions": {
    "max_age":   "7d",
    "max_docs":  1000,
    "max_size":  "5gb"
  }
}

這個api呼叫時自己給出新index的名稱
POST /my_alias/_rollover/my_new_index_name
{
  "conditions": {
    "max_age":   "7d",
    "max_docs":  1000,
    "max_size": "5gb"
  }
}

引數中不只是可以接收判斷條件，同時還可以接收新index的一些設定，mappings,alias等等， 就像在建立create index的api一樣
POST /logs_write/_rollover
{
  "conditions" : {
    "max_age": "7d",
    "max_docs": 1000,
    "max_size": "5gb"
  },
  "settings": {
    "index.number_of_shards": 2
  }
}
實際樣例：
POST http://192.168.199.103:9200/log_write/_rollover/log-1/
{
  "conditions": {
    "max_docs": 100
  },
  "settings": {
    "number_of_shards": 1,
    "number_of_replicas": 2
  },
  "mappings": {
    "log": {
      "properties": {
        "name": {
          "type": "text",
          "index": true
        },
        "message": {
          "type": "text",
          "index": true
        }
      }
    }
  },
  "aliases": {
    "log-1-write": {}
  }
}

{
"old_index": "logs",
"new_index": "log-1",
"rolled_over": true,
"dry_run": false,
"acknowledged": true,
"shards_acknowledged": true,
"conditions": {
"[max_docs: 100]": true
}
}

需要注意的是，如果在引數中不指定這些的話，那麼創建出來的新的index將什麼資料都不包含，mapping也是空的

7.PUT Mapping

put mapping API 允許我們給一個已經存在的index新增新的fields或者是改變現有欄位的搜尋模式。樣例：

PUT twitter 
{}
建立一個什麼都沒有的index，命名為twitter

PUT twitter/_mapping/_doc 
{
  "properties": {
    "email": {
      "type": "keyword"
    }
  }
}
給twitter index 新增一個型別為_doc,同時給_doc新增一個屬性email,型別為keyword

put mapping 可以支援多index(multi-index)引數， 也就是同時調整多個index的mapping，樣例：

# Create the two indices
PUT twitter-1
PUT twitter-2

# Update both mappings
PUT /twitter-1,twitter-2/_mapping/_doc 
{
  "properties": {
    "user_name": {
      "type": "text"
    }
  }
}

實際上在elasticsearch中通過put mapping只能給現有的屬性進行補充， 不能對現有的屬性進行更改，否則會丟擲異常，例如：

{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "mapper [name] of different type, current_type [text], merged_type [long]"
      }
    ],
    "type": "illegal_argument_exception",
    "reason": "mapper [name] of different type, current_type [text], merged_type [long]"
  },
  "status": 400
}
這是更新一個field 為name的型別， 原來為text,改為long，結果執行api的時候丟擲以上異常。

8.GET Mapping

get mapping api可以查詢一個或多個index的mapping資訊， 語法如下：

host:port/{index}/_mapping/{type}

樣例：查詢所有index中type為log的mapping,實際上沒有index都只有一個type
GET /_all/_mapping/log

結果：
{
  "log-1": {
    "mappings": {
      "log": {
        "properties": {
          "email": {
            "type": "text"
          },
          "name": {
            "type": "text"
          }
        }
      }
    }
  }
}

9.GET Field Mapping

get field mapping API可以用來查詢index中指定的一個或多個field資訊， 而不是一次性查詢一個index或多個index的所有mapping資訊

建立一個publications index
PUT publications
{
    "mappings": {
        "_doc": {
            "properties": {
                "id": { "type": "text" },
                "title":  { "type": "text"},
                "abstract": { "type": "text"},
                "author": {
                    "properties": {
                        "id": { "type": "text" },
                        "name": { "type": "text" }
                    }
                }
            }
        }
    }
}

獲取publications index 中_doc type 的title field 資訊， 同時顯示返回結果
GET publications/_mapping/_doc/field/title
{
   "publications": {
      "mappings": {
         "_doc": {
            "title": {
               "full_name": "title",
               "mapping": {
                  "title": {
                     "type": "text"
                  }
               }
            }
         }
      }
   }
}

get field mapping API 支援一次查詢多個field或者是查詢多個index的多個field

，它支援逗號運算子，_all, *號匹配等

如：

GET /twitter,kimchy/_mapping/field/message

GET /_all/_mapping/_doc,tweet,book/field/message,user.id

GET /_all/_mapping/_do*/field/*.id

GET publications/_mapping/_doc/field/a*