1、上机动手实战演练基于_version进行乐观锁并发控制
（1）先构造一条数据出来
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，先更新了一下这个数据
同时带上数据的版本号，确保说，es中的数据的版本号，跟客户端中的数据的版本号是相同的，才能修改
PUT /test_index/test_type/7?version=1
{
"test_field": "test client 1"
}
{
"_index": "test_index",
"_type": "test_type",
"_id": "7",
"_version": 2,
"result": "updated",
"_shards": {
"total": 2,
"successful": 1,
"failed": 0
},
"created": false
}
（4）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"
}
{
"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": "6m0G7yx7R1KECWWGnfH1sw",
"shard": "3",
"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": "6m0G7yx7R1KECWWGnfH1sw",
"shard": "3",
"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"
}
{
"_index": "test_index",
"_type": "test_type",
"_id": "7",
"_version": 3,
"result": "updated",
"_shards": {
"total": 2,
"successful": 1,
"failed": 0
},
"created": false
}
