1、上機動手實戰演練基於_version進行樂觀鎖併發控制
（1）先構造一條資料出來
PUT /test_index/test_type/7
{
"test_field": "test test"
}
（2）模擬兩個客戶端，都獲取到了同一條資料
GET test_index/test_type/7
{
"_index": "test_index",
"_type": "test_type",
"_id": "7",
"_version": 1,
"found": true,
"_source": {
"test_field": "test test"
}
}
（3）其中一個客戶端，先更新了一下這個資料
同時帶上資料的版本號，確保說，es中的資料的版本號，跟客戶端中的資料的版本號是相同的，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）另外一個客戶端，嘗試基於version=1的資料去進行修改，同樣帶上version版本號，進行樂觀鎖的併發控制
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）在樂觀鎖成功阻止併發問題之後，嘗試正確的完成更新
GET /test_index/test_type/7
{
"_index": "test_index",
"_type": "test_type",
"_id": "7",
"_version": 2,
"found": true,
"_source": {
"test_field": "test client 1"
}
}
基於最新的資料和版本號，去進行修改，修改後，帶上最新的版本號，可能這個步驟會需要反覆執行好幾次，才能成功，特別是在多執行緒併發更新同一條資料很頻繁的情況下
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
}