如果同一时刻多次更新都在执行，将面临并发问题。Elasticsearch支持并发控制，为每篇文档设置了一个版本号。乐观锁，如果更新发生冲突，目前的更新会失败
POST /secisland/_doc/1
{
"name":"张三",
"age": 23
}
# 查询时显示version
GET /secisland/_search?q=age:23&version=true
GET /secisland/_doc/1
{
"_index" : "secisland",
"_type" : "_doc",
"_id" : "1",
"_version" : 46,
"_seq_no" : 45,
"_primary_term" : 1,
"found" : true,
"_source" : {
"name" : "张三",
"age" : 24
}
}
version
冲突发生时自动重试更新retry_on_conflict
POST /secisland/_update/1?retry_on_conflict=2
{
"script": "ctx._source.age+=1"
}
seq_no
index文档时使用版本号，而不使用更新API。这种操作会覆盖现有文档。可以使用seq_no和primary_term实现并发控制
seq_no: The sequence number is increased with each operation and thus newer operations are guaranteed to have a higher sequence number than older operations. Elasticsearch can then use the sequence number of operations to make sure a newer document version is never overridden by a change that has a smaller sequence number assigned to it.
primary_term: 每当Primary Shard发生重新分配时，比如重启，Primary选举等，_primary_term会递增1。
PUT /secisland/_doc/1?if_seq_no=44&if_primary_term=1
{
"name":"张三",
"age": 23
}
使用外部版本
如果数据源是另一个数据存储，也许那里有版本控制系统。可以使用version=xx&version_type=external实现外部版本控制
