MongoDB对同一文档的并发更新不是原子的

问题描述

目前，我们有一个 orderId，我们为此向用户提供好处(发布).有多个事件可以触发福利/发布.但条件是只应触发 1 个事件.因此，为了处理当前请求，我们创建了一个布尔字段 POSTING_EVENT_SENT，最初设置为 false，之后任何能够将其标记为 true 的人都可以继续进行.

Currently, we have an orderId for which we give the benefit(posting) to the user. There are multiple events that can trigger benefit/posting. But the condition is that only 1 event should be triggered. Hence for handling current requests, we created a boolean field POSTING_EVENT_SENT, initially set to false, and later whoever was able to mark it as true can proceed further.

public boolean isOrderLockedAndUpdatedToTriggerPosting(String orderId, OrderStatus orderStatus) {

       Query query = new Query();
       query.addCriteria(Criteria.where(OrderConstants.ORDER_ID).is(orderId));
       query.addCriteria(Criteria.where(OrderConstants.POSTING_EVENT_SENT).is(false));
       Update update = new Update();
       update.set(OrderConstants.ORDER_STATUS, orderStatus);
       update.set(OrderConstants.UPDATED_AT, new Date());
       update.set(OrderConstants.UPDATED_IP_BY, deploymentProperties.getServerIp());
       update.set(OrderConstants.POSTING_EVENT_SENT, true);
       update.set(OrderConstants.UPDATED_BY, OrderConstants.UPDATED_BY_WORKER);
       UpdateResult result = mongoTemplate.updateFirst(query, update, OrderDetails.class);
       return result.getModifiedCount() > 0;
   }

这是代码试图执行的 mongodb 查询

this is the mongodb query that code is trying to execute

db.order.update({orderId : 123, paymentEventSent: false},{$set : {paymentEventSent: true}})

所以我们正在检查该字段是否为假，然后将其标记为真.所以理论上只有 1 个请求能够做到这一点，因为 mongo 查询是原子的.但是在我们的场景中，两个并发查询都成功地更新了记录.我们还缺少什么?

So we're checking if the field is false, then mark it to true. So theoretically only 1 request will be able to do the same, because the mongo queries are atomic. But in our scenario, both the concurrent queries were updating the records successfully. What else we're missing here?

推荐答案

使用条件更新并检查更新文档的数量以查看是否发生了更新.

Use conditional updates and examine the number of updated documents to see if the update happened.

require 'mongo'

client = Mongo::Client.new(['localhost:14400'])

coll = client['coll']

coll.delete_many
coll.insert_one(foo: 1)

rv = coll.update_one({foo: 1}, '$set' => {foo: 2})
if rv.modified_count == 1
  puts 'Updated'
end

rv = coll.update_one({foo: 1}, '$set' => {foo: 2})
if rv.modified_count == 1
  puts 'Updated'
end

https://github.com/p-mongo/tests/blob/master/query-conditional-update/test.rb

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