runtime: SQL Reader Async 10 times slower than sync

Hi,

we got a problem with the async sql reader. We can reproduce that in ef core and with the sql data reader. Its so slow, that it’s not usable. I also tried 4.5.0-preview2-26225-02, but the speed tests give the same result. Example: Async Sql Client

using (var conn = new System.Data.SqlClient.SqlConnection(getConnectionstring(_config)))
                    {
                        using (var cmd = new System.Data.SqlClient.SqlCommand("SELECT TOP 350 * FROM users.Users;", conn))
                        {
                            cmd.CommandType = System.Data.CommandType.Text;

                            conn.Open();
                            var reader = await cmd.ExecuteReaderAsync();

                            while (await reader.ReadAsync())
                            {
                                Guid id = reader.GetGuid(0);
                                stringBuilder2.AppendLine(id.ToString());
                            }
                        }
                    }

Result: 218ms

Sync Sql Client

    using (var conn = new System.Data.SqlClient.SqlConnection(getConnectionstring(_config)))
                    {
                        using (var cmd = new System.Data.SqlClient.SqlCommand("SELECT TOP 350 * FROM users.Users;", conn))
                        {
                            cmd.CommandType = System.Data.CommandType.Text;
                            conn.Open();
                            var reader = cmd.ExecuteReader();

                            while (reader.Read())
                            {
                                Guid id = reader.GetGuid(0);
                                stringBuilder.AppendLine(id.ToString());
                            }
                        }
                    }

Result: 28 ms

I always tried 10 or more times to exclude warmup.

The same happens using ef:

Sync ef example

                    using (var db = new TestContext(_config))
                    {
                       
                        db.ConfigureLogging(s => stringLogger.AppendLine(stopwatch.ElapsedMilliseconds.ToString() + " " + s));
                        var blogs = db.Users.Take(350)
                            .ToList();

                    
                    }

                    break;`

Result: ef-client took 22ms 0 Opening connection to database ‘users-service’ on server ‘xx.database.cloudapi.de’. 0 Opened connection to database ‘users-service’ on server ‘xx.database.cloudapi.de’. 0 Executing DbCommand [Parameters=[@__p_0=‘?’], CommandType=‘Text’, CommandTimeout=‘30’] SELECT TOP(@__p_0) [u].[Id], [u].[FirstName], [u].[LastName] FROM [users].[Users] AS [u] 21 Executed DbCommand (21ms) [Parameters=[@__p_0=‘?’], CommandType=‘Text’, CommandTimeout=‘30’] SELECT TOP(@__p_0) [u].[Id], [u].[FirstName], [u].[LastName] FROM [users].[Users] AS [u] 22 A data reader was disposed. 22 Closing connection to database ‘users-service’ on server ‘xx.database.cloudapi.de’. 22 Closed connection to database ‘users-service’ on server ‘xx.database.cloudapi.de’.

Async ef example:

using (var db = new TestContext(_config))
                    {
                      db.ConfigureLogging(s => stringLogger.AppendLine(stopwatch.ElapsedMilliseconds.ToString() + " " + s));
                        var blogs = await db.Users.Take(350)
                            .ToListAsync();

                
                    }

Result: ef-client-async took 197ms 0 Opening connection to database ‘users-service’ on server ‘xx.cloudapi.de’. 0 Opened connection to database ‘users-service’ on server ‘xx.database.cloudapi.de’. 0 Executing DbCommand [Parameters=[@__p_0=‘?’], CommandType=‘Text’, CommandTimeout=‘30’] SELECT TOP(@__p_0) [u].[Id], [u].[FirstName], [u].[LastName] FROM [users].[Users] AS [u] 125 Executed DbCommand (125ms) [Parameters=[@__p_0=‘?’], CommandType=‘Text’, CommandTimeout=‘30’] SELECT TOP(@__p_0) [u].[Id], [u].[FirstName], [u].[LastName] FROM [users].[Users] AS [u] 197 A data reader was disposed. 197 Closing connection to database ‘users-service’ on server ‘xx.database.cloudapi.de’. 197 Closed connection to database ‘users-service’ on server ‘xx.database.cloudapi.de’.

I would expect the async code to be slower but not 5 to 10 times.

I tried all available versions (preview 1, 2 and normal version).

My tests are generated with vs code on mac and in our docker images, e.g dotnet-nightly:2.1.0-preview1-runtime-stretch

Any ideas?