基于_version乐观锁并发控制

为基础思路

（1）先创建一条数据

PUT /test_index/test_type/7
{
"test_field": "test test"
}

（2）模拟两个客户端，都获取到了同一条数据

GET test_index/test_type/7

{
  "_index": "test_index",
  "_type": "test_type",
  "_id": "7",
  "_version": 1,
  "found": true,
  "_source": {
    "test_field": "test test"
  }
}

（3）其中一个客户端，先更新一下这条数据

PUT /test_index/test_type/7?version=1 
{
  "test_field": "test client 1"
}

返回结果:

{
  "_index": "test_index",
  "_type": "test_type",
  "_id": "7",
  "_version": 2,
  "result": "updated",
  "_shards": {
    "total": 2,
    "successful": 1,
    "failed": 0
  },
  "created": false
}

另外一个客户端，尝试基于version=1的数据去进行修改，同样带上version版本号，进行乐观锁的并发控制

PUT /test_index/test_type/7?version=1 
{
  "test_field": "test client 2"
}

则会出现报错

{
  "error": {
    "root_cause": [
      {
        "type": "version_conflict_engine_exception",
        "reason": "[test_type][7]: version conflict, current version [2] is different than the one provided [1]",
        "index_uuid": "cbDotlKxS7arKsfavEZgWQ",
        "shard": "1",
        "index": "test_index"
      }
    ],
    "type": "version_conflict_engine_exception",
    "reason": "[test_type][7]: version conflict, current version [2] is different than the one provided [1]",
    "index_uuid": "cbDotlKxS7arKsfavEZgWQ",
    "shard": "1",
    "index": "test_index"
  },
  "status": 409
}

（5）在乐观锁成功阻止并发问题之后，尝试正确的完成更新

GET /test_index/test_type/7
{
  "_index": "test_index",
  "_type": "test_type",
  "_id": "7",
  "_version": 2,
  "found": true,
  "_source": {
    "test_field": "test client 1"
  }
}

基于最新的数据和版本号，去进行修改，修改后，带上最新的版本号，可能这个步骤会需要反复执行好几次，才能成功，特别是在多线程并发更新同一条数据很频繁的情况下

PUT /test_index/test_type/7?version=2 
{
  "test_field": "test client 2"
}

返回结果:

{
  "_index": "test_index",
  "_type": "test_type",
  "_id": "7",
  "_version": 3,
  "result": "updated",
  "_shards": {
    "total": 2,
    "successful": 1,
    "failed": 0
  },
  "created": false
}