文档是不可改变的，不能修改他们。
如果想要更新现在有的文档，需要重建索引或者进行替换
不能访问旧版本的文档，但它不是立即删除的
PUT /website/blog/123
{
"title": "My first blog entry",
"text": "I am starting to get the hang of this...",
"date": "2014/01/02"
}
返回的结果：_version自增，created，表示不是create
{
"_index" : "website",
"_type" : "blog",
"_id" : "123",
"_version" : 2,
"created": false
}
可以利用_version来保证安全
put请求，（1）是指_version在1的时候才能更新
PUT /website/blog/1?version=1 (1)
{
"title": "My first blog entry",
"text": "Starting to get the hang of this..."
}
更新成功
{
"_index": "website",
"_type": "blog",
"_id": "1",
"_version": 2
"created": false
}
再次相同请求，则```490 Conflict
{
"error": {
"root_cause": [
{
"type": "version_conflict_engine_exception",
"reason": "[blog][1]: version conflict, current [2], provided [1]",
"index": "website",
"shard": "3"
}
],
"type": "version_conflict_engine_exception",
"reason": "[blog][1]: version conflict, current [2], provided [1]",
"index": "website",
"shard": "3"
},
"status": 409
}
外部系统保证安全
指定版本号需要大于ES当前版本号
创建外部版本号为5的博客
PUT /website/blog/2?version=5&version_type=external
{
"title": "My first external blog entry",
"text": "Starting to get the hang of this..."
}
成功响应：
{
"_index": "website",
"_type": "blog",
"_id": "2",
"_version": 5,
"created": true
}
更新这个文档，指定新版本号
PUT /website/blog/2?version=10&version_type=external
{
"title": "My first external blog entry",
"text": "This is a piece of cake..."
}
成功，失败则返回之前的冲突错误
{
"_index": "website",
"_type": "blog",
"_id": "2",
"_version": 10,
"created": false
}
