SQL Server 间歇性错误 40 无法打开与 SQL Server 的连接或找不到网络路径

Question

根据以下堆栈跟踪，我收到间歇性错误。我将 C# 实体框架与在单独的服务器计算机上运行的 SQL Server 2012 企业版一起使用。我可以从开发机器使用 SSMS 连接和查询数据库。

重新启动服务器计算机是问题的短期解决方案。然后连接再次工作，至少一段时间（数小时或数天）。

如何在不需要重新启动服务器计算机的情况下长期诊断或修复此问题？

Exception.ToString():

System.Data.Entity.Core.EntityException:
The underlying provider failed on Open. ---> 
System.Data.SqlClient.SqlException: 
A network-related or instance-specific error occurred while establishing a connection to SQL Server.
The server was not found or was not accessible. 
Verify that the instance name is correct and that SQL Server is configured to allow remote connections. 
(provider: Named Pipes Provider, error: 40 - 
Could not open a connection to SQL Server) ---> 
System.ComponentModel.Win32Exception: The network path was not found
   --- End of inner exception stack trace ---
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
   at System.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo, SqlInternalConnectionTds connHandler, Boolean ignoreSniOpenTimeout, Int64 timerExpire, Boolean encrypt, Boolean trustServerCert, Boolean integratedSecurity, B
oolean withFailover)
   at System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo serverInfo, String newPassword, SecureString newSecurePassword, Boolean ignoreSniOpenTimeout, TimeoutTimer timeout, Boolean withFailover)
   at System.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(ServerInfo serverInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString connectionOptions, SqlCredentia
l credential, TimeoutTimer timeout)
   at System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(TimeoutTimer timeout, SqlConnectionString connectionOptions, SqlCredential credential, String newPassword, SecureString newSecurePassword, Boolean redirectedU
serInstance)
   at System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, SqlCredential credential, Object providerInfo, String newPassword, SecureString newSecurePassw
ord, Boolean redirectedUserInstance, SqlConnectionString userConnectionOptions)
   at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions
 userOptions)
   at System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnectionPool pool, DbConnectionOptions options, DbConnectionPoolKey poolKey, DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectio
nInternal& connection)
   at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionClosed.TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
   at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.Open()
   at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.<>c__DisplayClass1.<Execute>b__0()
   at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
   at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Action operation)
   at System.Data.Entity.Core.EntityClient.EntityConnection.Open()
   --- End of inner exception stack trace ---
   at System.Data.Entity.Core.EntityClient.EntityConnection.Open()
   at System.Data.Entity.Core.Objects.ObjectContext.EnsureConnection()
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
   at System.Data.Entity.Core.Objects.ObjectContext.SaveChangesToStore(SaveOptions options, IDbExecutionStrategy executionStrategy)
   at System.Data.Entity.Core.Objects.ObjectContext.<>c__DisplayClass28.<SaveChanges>b__25()
   at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
   at System.Data.Entity.Core.Objects.ObjectContext.SaveChanges(SaveOptions options)
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
   at System.Data.Entity.DbContext.SaveChanges()
[followed by stacktrace in my code]

编辑

SQL Server 错误日志在错误发生时不显示任何内容。

我正在使用实体框架 6.0.1。

在出现异常并运行 SSMS 的机器与运行 SQL Server 的机器之间，有一根以太网电缆，然后是一个交换机 (A)，然后是另一根以太网电缆。此外，两台机器都有 WLAN，该 WLAN 连接到连接到路由器的苹果机场，路由器又连接到交换机 (B)，然后再连接到交换机 (A)。

连接字符串是：

<add name="xyzEntities" 
connectionString="metadata=res://*/Model1.csdl|res://*/Model1.ssdl|res://*/Model1.msl;
provider=System.Data.SqlClient;provider connection string=&quot;
data source=dt-pc;initial catalog=xyz;Integrated Security=True;
MultipleActiveResultSets=True;App=EntityFramework&quot;"
providerName="System.Data.EntityClient" />

服务器不在域中。它有专用的 IP 地址，一个用于 LAN，一个用于 WLAN。SSMS 使用 LAN IP 地址连接到服务器，而 C# 应用程序使用服务器名称。服务器和实例的名称是 dt-pc。

仔细想想，是不是应用程序有时会因为某些连接通过 WLAN 而失败？WLAN 不可靠。