Elastic Search 分布式特性

在 Elasticsearch 中，每个字段的所有数据都是默认被索引的。即每个字段都有为了快速检索设置的专用倒排索引。而且，不像其他多数的数据库，它能在同一个查询中使用所有这些倒排索引，并以惊人的速度返回结果。

文档

一个对象仅仅是类似于 hash 、 hashmap 、字典或者关联数组的 JSON 对象，对象中也可以嵌套其他的对象。对象可能包含了另外一些对象。

在 Elasticsearch 中，术语文档有着特定的含义。它是指最顶层或者根对象, 这个根对象被序列化成 JSON 并存储到 Elasticsearch 中，指定了唯一 ID。

文档元数据
_index：一个索引应该是因共同的特性被分组到一起的文档集合。类比数据库
_type：在索引中对数据进行逻辑分区。类比数据表
_id：当它和 _index 以及 _type 组合就可以唯一确定 Elasticsearch 中的一个文档。类比数据唯一标识

写数据

PUT /{index}/{type}/{id}
{
  "field": "value",
  ...
}

# For Example

 curl -X PUT "10.96.83.188:9200/website/blog/123" -H 'Content-Type: application/json' -d'
{
  "title": "My first blog entry",
  "text":  "Just trying this out...",
  "date":  "2014/01/01"
}
'
{"_index":"website","_type":"blog","_id":"123","_version":1,"result":"created",
"_shards":{"total":2,"successful":1,"failed":0},"created":true}

# 如果没有指定ID，Elasticsearch 可以帮我们自动生成 ID 
curl -X POST "10.96.83.188:9200/website/blog/" -H 'Content-Type: application/json' -d'
{
  "title": "My second blog entry",
  "text":  "Still trying this out...",
  "date":  "2014/01/01"
}
'
{"_index":"website","_type":"blog","_id":"AWoPmj2eBvBN4YG5RXks","_version":1,
"result":"created","_shards":{"total":2,"successful":1,"failed":0},"created":true}

读数据
pretty 为了让输出更友好

#取所有字段
curl -X GET "10.96.83.188:9200/website/blog/123?pretty"
{
  "_index" : "website",
  "_type" : "blog",
  "_id" : "123",
  "_version" : 1,
  "found" : true,
  "_source" : {
    "title" : "My first blog entry",
    "text" : "Just trying this out...",
    "date" : "2014/01/01"
  }
}

# 取部分字段
curl -X GET "10.96.83.188:9200/website/blog/123?_source=title,text&pretty"
{
  "_index" : "website",
  "_type" : "blog",
  "_id" : "123",
  "_version" : 1,
  "found" : true,
  "_source" : {
    "text" : "Just trying this out...",
    "title" : "My first blog entry"
  }
}

# 只取数据，不去元数据
 curl -X GET "10.96.83.188:9200/website/blog/123/_source"

{
  "title": "My first blog entry",
  "text":  "Just trying this out...",
  "date":  "2014/01/01"
}

# 读取多个数据
curl -X GET "10.96.83.188:9200/_mget?pretty" -H 'Content-Type: application/json' -d'
{
   "docs" : [
      {
         "_index" : "website",
         "_type" :  "blog",
         "_id" :    1
      },
      {
         "_index" : "website",
         "_type" :  "blog",
         "_id" :    124
      }
   ]
}
'

判断文档是否存在(200存在，404不存在)

$ curl -I -XHEAD "10.96.83.188:9200/website/blog/123/"
HTTP/1.1 200 OK
content-type: text/plain; charset=UTF-8
content-length: 0

$ curl -I -XHEAD "10.96.83.188:9200/website/blog/124/"
HTTP/1.1 404 Not Found
content-type: text/plain; charset=UTF-8
content-length: 0

更新操作

创建新文档

要么id保证唯一，要么不带id新建，由ES自动创建
创建时，带上_create，保证只新增，如果已存在则报错

curl -X PUT "10.96.83.188:9200/website/blog/123/_create" -H 'Content-Type: application/json' -d'
{
  "title": "My first blog entry",
  "text":  "I am starting to get the hang of this...",
  "date":  "2014/01/02"
}
'

{"error":{"root_cause":[{"type":"version_conflict_engine_exception","reason":"[blog][123]: version conflict, document already exists (current version [2])","index_uuid":"_sBTT-DdSnKytaOhbXEYfw","shard":"0","index":"website"}],"type":"version_conflict_engine_exception","reason":"[blog][123]: version conflict, document already exists (current version [2])","index_uuid":"_sBTT-DdSnKytaOhbXEYfw","shard":"0","index":"website"},"status":409}

删除文档

1 2	curl -X DELETE "10.96.83.188:9200/website/blog/123" {"found":true,"_index":"website","_type":"blog","_id":"123","_version":3,"result":"deleted","_shards":{"total":2,"successful":1,"failed":0}}

更新部分文档

curl -X POST "10.96.83.188:9200/website/blog/1/_update" -H 'Content-Type: application/json' -d'
{
   "doc" : {
      "tags" : [ "testing" ],
      "views": 0
   }
}
'

curl -X GET "10.96.83.188:9200/website/blog/1?pretty"
{
  "_index" : "website",
  "_type" : "blog",
  "_id" : "1",
  "_version" : 3,
  "found" : true,
  "_source" : {
    "title" : "My first blog entry",
    "text" : "Starting to get the hang of this...",
    "views" : 0,
    "tags" : [
      "testing"
    ]
  }
}

乐观并发控制