Elasticsearch处理并发读写操作

1. 并发控制的必要性

两个 Web 程序同时更新某个文档&＃xff0c;如果缺乏有效的并发&＃xff0c;会导致更改的数据丢失
悲观并发控制

• 假设有变更冲突的可能&＃xff0c;会对资源加锁&＃xff0c;防止冲突。例如数据库行锁

乐观并发控制

• 假设突然是不会发生的&＃xff0c;不会阻塞正在尝试的操作。如果数据在读写中被修改&＃xff0c;更新将会失败。应用程序决定如何解决冲突&＃xff0c;例如重试更新&＃xff0c;使用新的数据&＃xff0c;或者将错误报告给用户
• ES 采用的乐观并发控制
  

2. ES 的乐观并发控制

ES 中的文档是不可变更的。如果你更新一个文档&＃xff0c;会将会文档标记为删除&＃xff0c;同时增加一个全新当文档&＃xff0c;同时文档的 version 字段加 1
内部版本控制

• If_seq_no &＃43; If_primary_term

使用外部版本&＃xff08;使用其他数据库作为主要数据存储&＃xff09;

• version &＃43; version_type &＃61; external

3. demo

DELETE products
PUT products
PUT products/_doc/1
{"title":"iphone","count":100
}
返回输出&＃xff1a;
{"_index" : "products","_type" : "_doc","_id" : "1","_version" : 1,"result" : "created","_shards" : {"total" : 2,"successful" : 1,"failed" : 0},"_seq_no" : 0, "_primary_term" : 1
}GET products/_doc/1
{"_index" : "products","_type" : "_doc","_id" : "1","_version" : 1,"_seq_no" : 0,"_primary_term" : 1,"found" : true,"_source" : {"title" : "iphone","count" : 100}
}//只能执行一次
PUT products/_doc/1?if_seq_no&＃61;0&if_primary_term&＃61;1
{"title":"iphone","count":110
}返回输出&＃xff1a;_seq_no增1
{"_index" : "products","_type" : "_doc","_id" : "1","_version" : 2,"result" : "updated","_shards" : {"total" : 2,"successful" : 1,"failed" : 0},"_seq_no" : 1,"_primary_term" : 1
}#如果默认另外一个人查询
PUT products/_doc/1?if_seq_no&＃61;0&if_primary_term&＃61;1
{"title":"iphone","count":113
}
返回输出&＃xff1a;报错
{"error": {"root_cause": [{"type": "version_conflict_engine_exception","reason": "[1]: version conflict, required seqNo [0], primary term [1]. current document has seqNo [1] and primary term [1]","index_uuid": "V8OgL-0mQq6WST217HUCgA","shard": "0","index": "products"}],"type": "version_conflict_engine_exception","reason": "[1]: version conflict, required seqNo [0], primary term [1]. current document has seqNo [1] and primary term [1]","index_uuid": "V8OgL-0mQq6WST217HUCgA","shard": "0","index": "products"},"status": 409
}//数据库版本号为主
PUT products/_doc/1?version&＃61;23&version_type&＃61;external
{"title":"iphone","count":130
}返回输出&＃xff1a;
{"_index" : "products","_type" : "_doc","_id" : "1","_version" : 23,"result" : "updated","_shards" : {"total" : 2,"successful" : 1,"failed" : 0},"_seq_no" : 2,"_primary_term" : 1
}#查询GET products/_doc/1
返回输出&＃xff1a;
{"_index" : "products","_type" : "_doc","_id" : "1","_version" : 23,"_seq_no" : 2,"_primary_term" : 1,"found" : true,"_source" : {"title" : "iphone","count" : 130}
}