c# - ServiceStack/FluentNHibernate/MySQL - 两个并发请求使用相同的连接

Question

我们似乎遇到了一个奇怪的问题，即对我们服务的两个并发请求实际上使用了同一个数据库连接。

我们的设置是 ServiceStack + NHibernate + FluentNHibernate + MySQL。我已经设置了一个小测试来重现问题:

public class AppHost : AppHostBase
{
    private ISessionFactory _sessionFactory;

    public AppHost() : base("Lala Service", typeof(AppHost).Assembly)
    {
    }

    public override void Configure(Container container)
    {
        _sessionFactory = Fluently.Configure()

            .Database(MySQLConfiguration.Standard.ConnectionString(conn =>
                conn.Server("localhost").Username("lala").Password("lala").Database("lala")))

            .Mappings(mappings => mappings.AutoMappings.Add(
                AutoMap.Assembly(GetType().Assembly).Where(t => t == typeof(Lala))
                       .Conventions.Add(DefaultLazy.Never(), DefaultCascade.All())))

        .BuildSessionFactory();

        container.Register(c => _sessionFactory.OpenSession()).ReusedWithin(ReuseScope.Request);
    }
}

---

public class Lala
{
    public int    ID   { get; set; }
    public string Name { get; set; }
}

[Route("/lala")]
public class LalaRequest
{
}

public class LalaReseponse
{
}

---

public class LalaService : Service
{
    private ISession _session;

    public ISession Session1
    {
        get { return _session; }
        set { _session = value; }
    }

    public LalaReseponse Get(LalaRequest request)
    {
        var lala = new Lala
        {
            Name = Guid.NewGuid().ToString()
        };

        _session.Persist(lala);
        _session.Flush();

        lala.Name += " XXX";

        _session.Flush();

        return new LalaReseponse();
    }
}

我像这样通过 Ajax 同时点击此服务 10 次:

    <script type="text/javascript">
        for (i = 0; i < 10; i++) {
            console.log("aa");
            $.ajax({
                url:      '/lala',
                dataType: 'json',
                cache:    false
            });
        }
    </script>

结果始终是:

1. 打开的连接数 < 10。
2. 并非所有记录都已更新。
3. 有时 - 如果我删除记录，则会抛出 StaleObjectStateException。

这背后的原因是连接被两个并发请求重用，然后 LAST_INSERT_ID() 给出了错误行的 ID，因此两个请求正在更新同一行。

简而言之:它完全是一团糟，而且它显然在请求之间共享数据库连接。

问题是:为什么？我应该如何配置才能让每个请求从连接池获得自己的连接？

Answer 1

终于解决了，真是浪费一天时间!

问题的根源是NHibernate的connection release mode :

11.7. Connection Release Modes

The legacy (1.0.x) behavior of NHibernate in regards to ADO.NET connection management was that a ISession would obtain a connection when it was first needed and then hold unto that connection until the session was closed. NHibernate introduced the notion of connection release modes to tell a session how to handle its ADO.NET connections. ... The different release modes are identified by the enumerated values of NHibernate.ConnectionReleaseMode:

• OnClose - is essentially the legacy behavior described above. The NHibernate session obtains a connection when it first needs to perform some database access and holds unto that connection until the session is closed.

• AfterTransaction - says to release connections after a NHibernate.ITransaction has completed.

The configuration parameter hibernate.connection.release_mode is used to specify which release mode to use.

...

• after_transaction - says to use ConnectionReleaseMode.AfterTransaction. Note that with ConnectionReleaseMode.AfterTransaction, if a session is considered to be in auto-commit mode (i.e. no transaction was started) connections will be released after every operation.

这与 MySQL .NET/Connector 的默认连接池纠缠在一起，实际上意味着连接在并发请求之间交换，因为一个请求将连接释放回池中，而另一个请求获取它。

但是，我认为 NHibernate 在释放并重新获取连接后调用 LAST_INSERT_ID() 这一事实是一个错误。它应该在同一个“操作”中调用 LAST_INSERT_ID()。

无论如何，解决方案:

1. 使用交易，这是我们通常做的，或者

2. 如果您出于某种原因不能或不想在特定上下文中使用事务(这正是今天发生的情况)，请将连接 Release模式设置为“关闭时”。使用 FluentNHibernate 将是:

   .ExposeConfiguration(cfg =>
       cfg.SetProperty("connection.release_mode", "on_close"));
   

   从这里开始，即使没有事务，连接也会绑定(bind)到 session 。