I have a C# code that uses EntityFramework to execute a bunch of SQL statements: using (var context = new MyDbContext()) { context.Database.ExecuteSqlCommand(preparedQuery.QueryText); } The query is intended for updating a table with constantly chinging data, and to avoid race condition issues it uses Serializable transaction isolation level and UPDLOCK table hint. preparedQuery.QueryText
我有一个C＃代码使用EntityFramework来执行一堆SQL语句： using (var context = new MyDbContext()) { context.Database.ExecuteSqlCommand(preparedQuery.QueryText); } 该查询旨在用不断更新的数据更新表，并避免使用Serializable事务隔离级别和UPDLOCK表提示的争用条件问题。 preparedQuery.QueryText是一个如下所示的字符串： SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; BEGIN TRAN T11; DECLARE @Flag int; SET
The syntax of my query is good but not the output and it's really strange. I have the following table: | AppointID | UserID | AppointSet | AppointResolved | AppointStatus | AppointmentDatetime | 1 | 1 | 3/1/2011 | 3/1/2011 | 1 | 3/15/2011 | 2 | 1 | 3/2/2011 | 3/5/2011 | 4 | 3/16/2011 | 3 | 1 | 3/2/
我的查询语法很好，但不是输出，它真的很奇怪。 我有下表： | AppointID | UserID | AppointSet | AppointResolved | AppointStatus | AppointmentDatetime | 1 | 1 | 3/1/2011 | 3/1/2011 | 1 | 3/15/2011 | 2 | 1 | 3/2/2011 | 3/5/2011 | 4 | 3/16/2011 | 3 | 1 | 3/2/2011 | 3/11/2011 | 2 | 3/11
This question already has an answer here: Swift performance: sorting arrays 8 answers Building with: xcrun swift -Ofast test.swift -o test I'm getting times of: real 0m0.052s user 0m0.009s sys 0m0.005s Let's just concentrate on the answer to the question, which started with a "Why": Because you didn't turn optimisations on, and Swift relies heavily on compile
这个问题在这里已经有了答案： Swift性能：排序数组8个答案 搭建： xcrun swift -Ofast test.swift -o test 我得到的时间： real 0m0.052s user 0m0.009s sys 0m0.005s 我们只关注以“Why”开头的问题的答案：因为您没有优化，Swift严重依赖编译器优化。 这就是说，在C中进行图像处理确实很愚蠢。 这就是你拥有CGImage和朋友的原因。
I have been told this many times. But I don't know WHY...What extra cost is involved when allocating memory from heap? Is it hardware related? Is it related to CPU cycles? So many guesses but no exact answers...Could someone give me some elaboration? Just as "unwind" said, the Heap data structure is more complicated than Stack. And In my opinion, some memory space is allocate
我被告知了很多次。 但我不知道为什么......从堆中分配内存时涉及多大的额外成本？ 它与硬件相关吗？ 它与CPU周期有关吗？ 这么多的猜测，但没有确切的答案...有人可以给我一些阐述？ 就像“放松”一样，堆数据结构比堆栈更复杂。 在我看来，一些内存空间在开始运行时被分配给一个线程作为堆栈，而堆被进程内的所有线程共享。 这种范式需要一些额外的机制来管理每个线程对共享堆的使用，比如垃圾收集。 我对吗？ 因为堆
I understand lambdas and the Func and Action delegates. But expressions stump me. In what circumstances would you use an Expression<Func<T>> rather than a plain old Func<T> ? When you want to treat lambda expressions as expression trees and look inside them instead of executing them. For example, LINQ to SQL gets the expression and converts it to the equivalent SQL statemen
我了解lambda和Func和Action代表。 但表情让我感到难过。 在什么情况下你会使用Expression<Func<T>>而不是普通的旧Func<T> ？ 当你想把lambda表达式当作表达式树来看待它们而不是执行它们。 例如，LINQ to SQL获取表达式并将其转换为等效的SQL语句并将其提交给服务器（而不是执行lambda）。 从概念上讲， Expression<Func<T>>与Func<T>完全不同。 Func<T>表示一个delegate ，
One of the stated reasons for knowing assembler is that, on occasion, it can be employed to write code that will be more performant than writing that code in a higher-level language, C in particular. However, I've also heard it stated many times that although that's not entirely false, the cases where assembler can actually be used to generate more performant code are both extremely rare
了解汇编程序的其中一个原因是，有时它可以用来编写比用高级语言编写代码更具性能的代码，特别是C语言。 然而，我也多次听到它说过，虽然这并非完全错误，但汇编程序实际上可用于生成更高性能代码的情况非常罕见，需要有关汇编的专业知识和经验。 这个问题甚至没有涉及到汇编指令将是机器特定的和非便携式的，或者汇编器的其他方面的事实。 当然，除了这个之外，还有很多很好的理解组装的理由，但这是一个征求例子和数据的特
In C#/VB.NET/.NET, which loop runs faster, for or foreach ? Ever since I read that a for loop works faster than a foreach loop a long time ago I assumed it stood true for all collections, generic collections, all arrays, etc. I scoured Google and found a few articles, but most of them are inconclusive (read comments on the articles) and open ended. What would be ideal is to have each scenar
在C＃/ VB.NET / .NET中，哪个循环运行速度更快，是for或foreach ？ 自从我读了一个for循环比foreach循环的工作更快，很久以前我就认为它适用于所有集合，泛型集合，所有数组等等。 我搜索了谷歌并发现了一些文章，但其中大多数都没有结果（阅读文章的评论）并且是开放式的。 最理想的是将每个场景列出并提供相同的最佳解决方案。 例如（只是它应该如何的一个例子）： 用于迭代1000个以上字符串的数组 - for比foreach
Or is it now the other way around? From what I've heard there are some areas in which C# proves to be faster than C++, but I've never had the guts to test it by myself. Thought any of you could explain these differences in detail or point me to the right place for information on this. There is no strict reason why a bytecode based language like C# or Java that has a JIT cannot be as
或者现在是另一种方式？ 从我听说的有一些地方C＃证明比C ++更快，但我从来没有胆量来自己测试它。 想到你们任何一个人都可以详细解释这些差异，或者指出我在这方面的信息的正确位置。 没有严格的原因，为什么像C＃或Java这样的基于字节码的语言具有JIT不能像C ++代码那么快。 然而，C ++代码在很长一段时间里过去显得更快，而今天在很多情况下也是如此。 这主要是由于更高级的JIT优化实施起来很复杂，而且非常酷的只是
I have a strange habit it seems... according to my co-worker at least. We've been working on a small project together. The way I wrote the classes is (simplified example): [Serializable()] public class Foo { public Foo() { } private Bar _bar; public Bar Bar { get { if (_bar == null) _bar = new Bar(); return _bar
至少据我的同事说，我似乎有一种奇怪的习惯。 我们一直在一起开展一个小项目。 我写这些类的方式是（简化示例）： [Serializable()] public class Foo { public Foo() { } private Bar _bar; public Bar Bar { get { if (_bar == null) _bar = new Bar(); return _bar; } set { _bar = value; } } } 所以，基本上，我
I read everywhere that ternary operator is supposed to be faster than, or at least the same as, its equivalent if - else block. However, I did the following test and found out it's not the case: Random r = new Random(); int[] array = new int[20000000]; for(int i = 0; i < array.Length; i++) { array[i] = r.Next(int.MinValue, int.MaxValue); } Array.Sort(array); long value = 0; DateTim
我读的是无处不在三元运营商应该是比快，或至少一样的，它的等效if - else块。 但是，我做了以下测试，发现情况并非如此： Random r = new Random(); int[] array = new int[20000000]; for(int i = 0; i < array.Length; i++) { array[i] = r.Next(int.MinValue, int.MaxValue); } Array.Sort(array); long value = 0; DateTime begin = DateTime.UtcNow; foreach (int i in array) { if (i > 0) {