Elasticsearch system learning (seven) -ES concurrency control

A, ES concurrency control principle

1.1, ES concurrency conflicts

1.2, optimistic and pessimistic locking concurrency control lock illustrated

Based on internal ES _version for optimistic concurrency control lock :

Second, the practice of concurrency control

2.1, based on _version for optimistic concurrency control lock

1) Construction of Data

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

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

2) simulate two clients, we have acquired the same data

GET /test_index/test_type/7

{
  "_index": "test_index",
  "_type": "test_type",
  "_id": "7",
  "_version": 1,   #此时版本号是1
  "found": true,
  "_source": {
    "test_field": "test test"
  }
}

3）模拟一个客户端，先更新了这个数据

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,   #此时实际版本号已经变成2了
  "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]",   #版本冲突
        "index_uuid": "6t1NqhChSpyuYY7m-Eq2jA",
        "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": "6t1NqhChSpyuYY7m-Eq2jA",
    "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

首先获取正确的版本号

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，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,   #修改成功，版本号再次更改
  "result": "updated",
  "_shards": {
    "total": 2,
    "successful": 1,
    "failed": 0
  },
  "created": false
}