When running with Aurora MySQL, the application stops when the second query is issued.

The issue

The following code works fine for local MySQL 5.7, but when run on AWS 5.7.mysql_aurora.2.07.2, it stops working when the second query is issued. Also, synchronous execution will stop when the second query is issued as well.

var hostBuilder = Host.CreateDefaultBuilder(args)
    .ConfigureServices((context, services) =>
    {
        services.AddDbContext<MyDbContext>(options =>
        {
            const string connectionString = "Server=aurora-mysql-master.enhance.xxxxx.jp;Port=3306;Uid=xxxx;Pwd=xxx;Database=xxx;";
            optionsUseMySql(connectionString, new MySqlServerVersion(new Version(5, 7))).EnableDetailedErrors();
        });
        services.AddSingleton<App>();
    });

await hostBuilder.Build().Services
    .GetRequiredService<App>()
    .RunAsync();

public class App
{
    private readonly MyDbContext _myDbContext;
    public App(MyDbContext myDbContext)
    {
        _myDbContext = myDbContext;
    }

    public async Task RunAsync()
    {
        Log.Information("count={count}", await _myDbContext.Users.AsNoTracking().CountAsync());
        Log.Information("count={count}", await _myDbContext.Users.AsNoTracking().CountAsync()); // App Stoped
        //Log.Information("count={count}", _myDbContext.Users.AsNoTracking().Count());
        //Log.Information("count={count}", _myDbContext.Users.AsNoTracking().Count()); // App Stoped
    }
}

From the log, it looks like execution is stopped for a long time at the database connection when the second query is executed.

[10:30:08 DBG] [Microsoft.EntityFrameworkCore.Infrastructure] An 'IServiceProvider' was created for internal use by Entity Framework.
[10:58:03 INF] [Microsoft.EntityFrameworkCore.Infrastructure] Entity Framework Core 6.0.1 initialized 'MyDbContext' using provider 'Pomelo.EntityFrameworkCore.MySql:6.0.1' with options: DetailedErrorsEnabled ServerVersion 5.7-mysql
[10:58:03 DBG] [Microsoft.EntityFrameworkCore.Query] Compiling query expression:
'DbSet<User>()
    .AsNoTracking()
    .Count()'
[10:58:03 DBG] [Microsoft.EntityFrameworkCore.Query] Generated query execution expression:
'queryContext => ShapedQueryCompilingExpressionVisitor.SingleAsync<int>(
    asyncEnumerable: new SingleQueryingEnumerable<int>(
        (RelationalQueryContext)queryContext,
        RelationalCommandCache.SelectExpression(
            Projection Mapping:
                EmptyProjectionMember -> 0
            SELECT COUNT(*)
            FROM USER AS i),
        Func<QueryContext, DbDataReader, ResultContext, SingleQueryResultCoordinator, int>,
        ConsoleApp24.MyDbContext,
        False,
        True,
        True
    ),
    cancellationToken: queryContext.CancellationToken)'
[10:58:03 DBG] [Microsoft.EntityFrameworkCore.Database.Command] Creating DbCommand for 'ExecuteReader'.
[10:58:03 DBG] [Microsoft.EntityFrameworkCore.Database.Command] Created DbCommand for 'ExecuteReader' (11ms).
[10:58:03 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Opening connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxxx.jp'.
[10:58:04 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Opened connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxxx.jp'.
[10:58:04 DBG] [Microsoft.EntityFrameworkCore.Database.Command] Executing DbCommand [Parameters=[], CommandType='Text', CommandTimeout='30']
SELECT COUNT(*)
FROM `USER` AS `i`
[10:58:04 INF] [Microsoft.EntityFrameworkCore.Database.Command] Executed DbCommand (35ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
SELECT COUNT(*)
FROM `USER` AS `i`
[10:58:04 DBG] [Microsoft.EntityFrameworkCore.Database.Command] A data reader was disposed.
[10:58:04 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Closing connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxxx.jp'.
[10:58:04 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Closed connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxxx.jp'.
[10:58:04 INF] [] count=127797
[10:58:26 DBG] [Microsoft.EntityFrameworkCore.Database.Command] Creating DbCommand for 'ExecuteReader'.
[10:58:26 DBG] [Microsoft.EntityFrameworkCore.Database.Command] Created DbCommand for 'ExecuteReader' (13ms).
[10:58:26 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Opening connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxxx.jp'.

If pooling is disabled in the connection string, the second query will also succeed. We would like to consider other ways to deal with this because of the performance issues.

const string connectionString = "Server=aurora-mysql-master.enhance.xxxxx.jp;Port=3306;Uid=xxxx;Pwd=xxx;Database=xxx;Pooling=false";

[11:36:40 DBG] [Microsoft.EntityFrameworkCore.Infrastructure] An 'IServiceProvider' was created for internal use by Entity Framework.
[11:36:45 INF] [Microsoft.EntityFrameworkCore.Infrastructure] Entity Framework Core 6.0.1 initialized 'MyDbContext' using provider 'Pomelo.EntityFrameworkCore.MySql:6.0.1' with options: DetailedErrorsEnabled ServerVersion 5.7-mysql
[11:36:45 DBG] [Microsoft.EntityFrameworkCore.Query] Compiling query expression:
'DbSet<User>()
    .AsNoTracking()
    .Count()'
[11:36:45 DBG] [Microsoft.EntityFrameworkCore.Query] Generated query execution expression:
'queryContext => ShapedQueryCompilingExpressionVisitor.SingleAsync<int>(
    asyncEnumerable: new SingleQueryingEnumerable<int>(
        (RelationalQueryContext)queryContext,
        RelationalCommandCache.SelectExpression(
            Projection Mapping:
                EmptyProjectionMember -> 0
            SELECT COUNT(*)
            FROM USER AS i),
        Func<QueryContext, DbDataReader, ResultContext, SingleQueryResultCoordinator, int>,
        ConsoleApp24.MyDbContext,
        False,
        True,
        True
    ),
    cancellationToken: queryContext.CancellationToken)'
[11:36:45 DBG] [Microsoft.EntityFrameworkCore.Database.Command] Creating DbCommand for 'ExecuteReader'.
[11:36:45 DBG] [Microsoft.EntityFrameworkCore.Database.Command] Created DbCommand for 'ExecuteReader' (16ms).
[11:36:45 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Opening connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxx.jp'.
[11:36:46 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Opened connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxx.jp'.
[11:36:46 DBG] [Microsoft.EntityFrameworkCore.Database.Command] Executing DbCommand [Parameters=[], CommandType='Text', CommandTimeout='30']
SELECT COUNT(*)
FROM `USER` AS `i`
[11:36:46 INF] [Microsoft.EntityFrameworkCore.Database.Command] Executed DbCommand (49ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
SELECT COUNT(*)
FROM `USER` AS `i`
[11:36:46 DBG] [Microsoft.EntityFrameworkCore.Database.Command] A data reader was disposed.
[11:36:46 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Closing connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxx.jp'.
[11:36:46 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Closed connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxx.jp'.
[11:36:46 INF] [] count=127797
[11:36:47 DBG] [Microsoft.EntityFrameworkCore.Database.Command] Creating DbCommand for 'ExecuteReader'.
[11:36:47 DBG] [Microsoft.EntityFrameworkCore.Database.Command] Created DbCommand for 'ExecuteReader' (1ms).
[11:36:47 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Opening connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxx.jp'.
[11:36:47 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Opened connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxx.jp'.
[11:36:47 DBG] [Microsoft.EntityFrameworkCore.Database.Command] Executing DbCommand [Parameters=[], CommandType='Text', CommandTimeout='30']
SELECT COUNT(*)
FROM `USER` AS `i`
[11:36:47 INF] [Microsoft.EntityFrameworkCore.Database.Command] Executed DbCommand (16ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
SELECT COUNT(*)
FROM `USER` AS `i`
[11:36:47 DBG] [Microsoft.EntityFrameworkCore.Database.Command] A data reader was disposed.
[11:36:47 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Closing connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxx.jp'.
[11:36:47 DBG] [Microsoft.EntityFrameworkCore.Database.Connection] Closed connection to database 'xxx' on server 'aurora-mysql-master.enhance.xxxx.jp'.
[11:36:47 INF] [] count=127797

Further technical details

Aurora MySQL Information

• Engine version 5.7.mysql_aurora.2.07.2

Operating system: Windows Pomelo.EntityFrameworkCore.MySql version: 6.0.1 Microsoft.AspNetCore.App version:

Other details about my project setup:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Hosting" Version="6.0.1" />
    <PackageReference Include="Pomelo.EntityFrameworkCore.MySql" Version="6.0.1" />
    <PackageReference Include="Serilog.Extensions.Hosting" Version="4.2.0" />
    <PackageReference Include="Serilog.Extensions.Logging" Version="3.1.0" />
    <PackageReference Include="Serilog.Settings.Configuration" Version="3.3.0" />
    <PackageReference Include="Serilog.Sinks.Console" Version="4.0.1" />
  </ItemGroup>

</Project>

[mguinness]

Thanks for doing the research to track down this issue, documented at MySqlConnection.Open Freezes with Amazon Aurora.

The cause of this problem is Amazon Aurora not correctly supporting pipelining in the MySQL protocol. This is known to be a problem with 2.x versions of Aurora (that implement MySQL 5.7), but not with 3.x versions (that implement MySQL 8.0).

[karuakun]

Resolved.

Added to ConnectionStrings as suggested in the next page.Pipelining = False https://mysqlconnector.net/troubleshooting/aurora-freeze/

const string connectionStrings = "Server=aurora-mysql-master.enhance.xxxx.jp;Port=3306;Uid=xxx;Pwd=xxx;Database=xxx;Pipelining=False";