Cosmos DB，如果我在使用 SkipToken 查询时更新某些项目会发生啥？

Posted 2023-02-16

【中文标题】Cosmos DB，如果我在使用 SkipToken 查询时更新某些项目会发生啥？

【英文标题】：Cosmos DB, What will happen If I update some item when query with SkipToken?Cosmos DB，如果我在使用 SkipToken 查询时更新某些项目会发生什么？

【发布时间】：2021-07-13 11:19:20

【问题描述】：

如果我使用 SkipToken 从 CosmosDB 查询项目，

喜欢伪代码：

do
   var page = Query();
   foreach(var item in page)
   
      Update(item);
   
while(HasNextPage());

我得到的page可能不完整，这意味着我会错过一些项目。

但如果我在Update 之后稍等片刻 喜欢：

do
   var page = Query();
   foreach(var item in page)
   
      Update(item);
   

   // difference here:
   WaitAMoment();
while(HasNextPage());

，错误不会发生，我会得到我需要的完整页面。

那么这个过程发生了什么？

【问题讨论】：

您能添加Query() 的详细信息吗？使用sql，我可能会尝试在我身边重现问题。

【参考方案1】：

您不必在代码中等待，此功能由 CosmosDB 内部处理。查看Pagination in SDKs of Cosmos DB，例如，我在下面的 C# 中添加处理服务器端分页的代码（了解它的工作原理）：

private static async Task QueryPartitionedContainerInParallelAsync(Container container)
        
            List<Family> familiesSerial = new List<Family>();
            string queryText = "SELECT * FROM Families";

            // 0 maximum parallel tasks, effectively serial execution
            QueryRequestOptions options = new QueryRequestOptions()  MaxBufferedItemCount = 100 ;
            options.MaxConcurrency = 0;
            using (FeedIterator<Family> query = container.GetItemQueryIterator<Family>(
                queryText,
                requestOptions: options))
            
                while (query.HasMoreResults)
                
                    foreach (Family family in await query.ReadNextAsync())
                    
                        familiesSerial.Add(family);
                    
                
            

            Assert("Parallel Query expected two families", familiesSerial.ToList().Count == 2);

            // 1 maximum parallel tasks, 1 dedicated asynchronous task to continuously make REST calls
            List<Family> familiesParallel1 = new List<Family>();

            options.MaxConcurrency = 1;
            using (FeedIterator<Family> query = container.GetItemQueryIterator<Family>(
                queryText,
                requestOptions: options))
            
                while (query.HasMoreResults)
                
                    foreach (Family family in await query.ReadNextAsync())
                    
                        familiesParallel1.Add(family);
                    
                
            

            Assert("Parallel Query expected two families", familiesParallel1.ToList().Count == 2);
            AssertSequenceEqual("Parallel query returns result out of order compared to serial execution", familiesSerial, familiesParallel1);


            // 10 maximum parallel tasks, a maximum of 10 dedicated asynchronous tasks to continuously make REST calls
            List<Family> familiesParallel10 = new List<Family>();

            options.MaxConcurrency = 10;
            using (FeedIterator<Family> query = container.GetItemQueryIterator<Family>(
                queryText,
                requestOptions: options))
            
                while (query.HasMoreResults)
                
                    foreach (Family family in await query.ReadNextAsync())
                    
                        familiesParallel10.Add(family);
                    
                
            

            Assert("Parallel Query expected two families", familiesParallel10.ToList().Count == 2);
            AssertSequenceEqual("Parallel query returns result out of order compared to serial execution", familiesSerial, familiesParallel10);