Ran*_*rez 5 c# sql-server performance async-await iasyncenumerable
我目前正在测试 C# 8 的异步流，似乎当我尝试使用使用 async/await 并返回 Task> 的旧模式运行应用程序时，它似乎更快。（我使用秒表对其进行测量并尝试多次运行，结果是我提到的旧模式似乎比使用 IAsyncEnumerable 快一些）。
这是我写的一个简单的控制台应用程序（我也在想我可能以错误的方式从数据库加载数据）
class Program
{
static async Task Main(string[] args)
{
// Using the old pattern
//Stopwatch stopwatch = Stopwatch.StartNew();
//foreach (var person in await LoadDataAsync())
//{
// Console.WriteLine($"Id: {person.Id}, Name: {person.Name}");
//}
//stopwatch.Stop();
//Console.WriteLine(stopwatch.ElapsedMilliseconds);
Stopwatch stopwatch = Stopwatch.StartNew();
await foreach (var person in LoadDataAsyncStream())
{
Console.WriteLine($"Id: {person.Id}, Name: {person.Name}");
}
stopwatch.Stop();
Console.WriteLine(stopwatch.ElapsedMilliseconds);
Console.ReadKey();
}
static async Task<IEnumerable<Person>> LoadDataAsync()
{
string connectionString = "Server=localhost; Database=AsyncStreams; Trusted_Connection = True;";
var people = new List<Person>();
using (SqlConnection connection = new SqlConnection(connectionString))
{
//SqlDataReader
await connection.OpenAsync();
string sql = "Select * From Person";
SqlCommand command = new SqlCommand(sql, connection);
using (SqlDataReader dataReader = await command.ExecuteReaderAsync())
{
while (await dataReader.ReadAsync())
{
Person person = new Person();
person.Id = Convert.ToInt32(dataReader[nameof(Person.Id)]);
person.Name = Convert.ToString(dataReader[nameof(Person.Name)]);
person.Address = Convert.ToString(dataReader[nameof(Person.Address)]);
person.Occupation = Convert.ToString(dataReader[nameof(Person.Occupation)]);
person.Birthday = Convert.ToDateTime(dataReader[nameof(Person.Birthday)]);
person.FavoriteColor = Convert.ToString(dataReader[nameof(Person.FavoriteColor)]);
person.Quote = Convert.ToString(dataReader[nameof(Person.Quote)]);
person.Message = Convert.ToString(dataReader[nameof(Person.Message)]);
people.Add(person);
}
}
await connection.CloseAsync();
}
return people;
}
static async IAsyncEnumerable<Person> LoadDataAsyncStream()
{
string connectionString = "Server=localhost; Database=AsyncStreams; Trusted_Connection = True;";
using (SqlConnection connection = new SqlConnection(connectionString))
{
//SqlDataReader
await connection.OpenAsync();
string sql = "Select * From Person";
SqlCommand command = new SqlCommand(sql, connection);
using (SqlDataReader dataReader = await command.ExecuteReaderAsync())
{
while (await dataReader.ReadAsync())
{
Person person = new Person();
person.Id = Convert.ToInt32(dataReader[nameof(Person.Id)]);
person.Name = Convert.ToString(dataReader[nameof(Person.Name)]);
person.Address = Convert.ToString(dataReader[nameof(Person.Address)]);
person.Occupation = Convert.ToString(dataReader[nameof(Person.Occupation)]);
person.Birthday = Convert.ToDateTime(dataReader[nameof(Person.Birthday)]);
person.FavoriteColor = Convert.ToString(dataReader[nameof(Person.FavoriteColor)]);
person.Quote = Convert.ToString(dataReader[nameof(Person.Quote)]);
person.Message = Convert.ToString(dataReader[nameof(Person.Message)]);
yield return person;
}
}
await connection.CloseAsync();
}
}
我想知道 IAsyncEnumerable 是不是最适合这种场景，还是我在使用 IAsyncEnumerable 时查询数据的方式有问题？我可能是错的，但我实际上希望使用 IAsyncEnumerable 会更快。（顺便说一句......差异通常在数百毫秒内）
我使用 10,000 行的示例数据尝试了该应用程序。
这也是用于填充数据的代码，以防万一......
static async Task InsertDataAsync()
{
string connectionString = "Server=localhost; Database=AsyncStreams; Trusted_Connection = True;";
using (SqlConnection connection = new SqlConnection(connectionString))
{
string sql = $"Insert Into Person (Name, Address, Birthday, Occupation, FavoriteColor, Quote, Message) Values";
for (int i = 0; i < 1000; i++)
{
sql += $"('{"Randel Ramirez " + i}', '{"Address " + i}', '{new DateTime(1989, 4, 26)}', '{"Software Engineer " + i}', '{"Red " + i}', '{"Quote " + i}', '{"Message " + i}'),";
}
using (SqlCommand command = new SqlCommand(sql.Remove(sql.Length - 1), connection))
{
command.CommandType = CommandType.Text;
await connection.OpenAsync();
await command.ExecuteNonQueryAsync();
await connection.CloseAsync();
}
}
}
IAsyncEnumerable<T>本质上并不比 更快或更慢Task<T>。这取决于实施。
IAsyncEnumerable<T>是关于尽快异步检索提供单独值的数据。
IAsyncEnumerable<T>允许批量生成值，这将使一些调用同步MoveNextAsync，如下例所示：
async Task Main()
{
var hasValue = false;
var asyncEnumerator = GetValuesAsync().GetAsyncEnumerator();
do
{
var task = asyncEnumerator.MoveNextAsync();
Console.WriteLine($"Completed synchronously: {task.IsCompleted}");
hasValue = await task;
if (hasValue)
{
Console.WriteLine($"Value={asyncEnumerator.Current}");
}
}
while (hasValue);
await asyncEnumerator.DisposeAsync();
}
async IAsyncEnumerable<int> GetValuesAsync()
{
foreach (var batch in GetValuesBatch())
{
await Task.Delay(1000);
foreach (var value in batch)
{
yield return value;
}
}
}
IEnumerable<IEnumerable<int>> GetValuesBatch()
{
yield return Enumerable.Range(0, 3);
yield return Enumerable.Range(3, 3);
yield return Enumerable.Range(6, 3);
}
输出：
Completed synchronously: False
Value=0
Completed synchronously: True
Value=1
Completed synchronously: True
Value=2
Completed synchronously: False
Value=3
Completed synchronously: True
Value=4
Completed synchronously: True
Value=5
Completed synchronously: False
Value=6
Completed synchronously: True
Value=7
Completed synchronously: True
Value=8
Completed synchronously: True