NLog-MySQL数据库目标发生StackOverflow异常/NLog.NLogRuntimeException

Question

I've configured NLog to log errors/logs to two MySQL/Database targets:

<nlog autoReload="false" internalLogFile="omg.txt" throwExceptions="true" xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <!--<nlog autoReload="false" xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">-->
  <variable name="DefaultLayout" value="${longdate} | ${uppercase:${level}} | ${logger} | ${message}&#xD;&#xA;     ${exception:innerFormat=ToString:maxInnerExceptionLevel=6:innerExceptionSeparator=InnerException:format=ToString}" />
  <targets>
    <target xsi:type="ColoredConsole" name="console" layout="${DefaultLayout}" />
    <target xsi:type="Null" name="nulltarget" formatMessage="false" layout="${DefaultLayout}" />
    <target xsi:type="Database"
          name="MySqlErrorTarget"
          dbProvider="MySql.Data.MySqlClient" connectionString="x"
          keepConnection="true">
      <commandText>
        CALL Error_Insert(@Message)
      </commandText>
      <parameter name="@Message" layout="${message}" />
      (...)
    </target>
    <target xsi:type="Database"
          name="MySqlLogTarget"
          dbProvider="MySql.Data.MySqlClient" connectionString="x"
          keepConnection="true">
      <commandText>
        CALL Log_Insert(@Message)
      </commandText>
      <parameter name="@Message" layout="${message}" />
      (...)
    </target>
  </targets>
  <rules>
    <logger name="*" levels="TRACE, DEBUG, INFO" writeTo="MySqlLogTarget"/>
    <logger name="*" levels="WARN, ERROR, FATAL" writeTo="MySqlErrorTarget"/>
    <logger name="*" minlevel="INFO" writeTo="console" />
  </rules>
</nlog>

When MySQL database is available everything works great, however when MySQL goes down, NLog throws StackOverflow exception. Internal log file looks like follows:

2016-03-21 15:36:33.0487 Error Error when writing to database MySql.Data.MySqlClient.MySqlException (0x80004005): Unable to connect to any of the specified MySQL hosts. ---> System.Net.Sockets.SocketException (0x80004005): No such host is known
   at System.Net.Dns.GetAddrInfo(String name)
   at System.Net.Dns.InternalGetHostByName(String hostName, Boolean includeIPv6)
   at System.Net.Dns.GetHostEntry(String hostNameOrAddress)
   at MySql.Data.Common.MyNetworkStream.CreateStream(MySqlConnectionStringBuilder settings, Boolean unix)
   at MySql.Data.Common.StreamCreator.GetStream(MySqlConnectionStringBuilder settings)
   at MySql.Data.MySqlClient.NativeDriver.Open()
   at MySql.Data.MySqlClient.NativeDriver.Open()
   at MySql.Data.MySqlClient.Driver.Open()
   at MySql.Data.MySqlClient.Driver.Create(MySqlConnectionStringBuilder settings)
   at MySql.Data.MySqlClient.MySqlPool.GetPooledConnection()
   at MySql.Data.MySqlClient.MySqlPool.TryToGetDriver()
   at MySql.Data.MySqlClient.MySqlPool.GetConnection()
   at MySql.Data.MySqlClient.MySqlConnection.Open()
   at NLog.Targets.DatabaseTarget.OpenConnection(String connectionString)
   at NLog.Targets.DatabaseTarget.EnsureConnectionOpen(String connectionString)
   at NLog.Targets.DatabaseTarget.WriteEventToDatabase(LogEventInfo logEvent)
   at NLog.Targets.DatabaseTarget.Write(LogEventInfo logEvent)
2016-03-21 15:37:00.1794 Error Error when writing to database MySql.Data.MySqlClient.MySqlException (0x80004005): Unable to connect to any of the specified MySQL hosts. ---> System.Net.Sockets.SocketException (0x80004005): No such host is known
   at System.Net.Dns.GetAddrInfo(String name)
   at System.Net.Dns.InternalGetHostByName(String hostName, Boolean includeIPv6)
   at System.Net.Dns.GetHostEntry(String hostNameOrAddress)
   at MySql.Data.Common.MyNetworkStream.CreateStream(MySqlConnectionStringBuilder settings, Boolean unix)
   at MySql.Data.Common.StreamCreator.GetStream(MySqlConnectionStringBuilder settings)
   at MySql.Data.MySqlClient.NativeDriver.Open()
   at MySql.Data.MySqlClient.NativeDriver.Open()
   at MySql.Data.MySqlClient.Driver.Open()
   at MySql.Data.MySqlClient.Driver.Create(MySqlConnectionStringBuilder settings)
   at MySql.Data.MySqlClient.MySqlPool.GetPooledConnection()
   at MySql.Data.MySqlClient.MySqlPool.TryToGetDriver()
   at MySql.Data.MySqlClient.MySqlPool.GetConnection()
   at MySql.Data.MySqlClient.MySqlConnection.Open()
   at NLog.Targets.DatabaseTarget.OpenConnection(String connectionString)
   at NLog.Targets.DatabaseTarget.EnsureConnectionOpen(String connectionString)
   at NLog.Targets.DatabaseTarget.WriteEventToDatabase(LogEventInfo logEvent)
   at NLog.Targets.DatabaseTarget.Write(LogEventInfo logEvent)

This goes infinitely, thus in the end StackOverflow occurs. Exception reported in Visual Studio looks like follows:

NLog.NLogRuntimeException occurred
  HResult=-2146233088
  Message=Exception occurred in NLog
  Source=NLog
  StackTrace:
       at NLog.LoggerImpl.<>c__DisplayClass1.<Write>b__0(Exception ex)
       at NLog.Internal.SingleCallContinuation.Function(Exception exception)
       at NLog.Targets.Target.Write(AsyncLogEventInfo logEvent)
       at NLog.Targets.Target.WriteAsyncLogEvent(AsyncLogEventInfo logEvent)
       at NLog.LoggerImpl.WriteToTargetWithFilterChain(TargetWithFilterChain targetListHead, LogEventInfo logEvent, AsyncContinuation onException)
       at NLog.LoggerImpl.Write(Type loggerType, TargetWithFilterChain targets, LogEventInfo logEvent, LogFactory factory)
       at NLog.Logger.Debug(String message)
       at Runner.Main(String[] args) in C:\Repos\x\src\Runner.cs:line 36
  InnerException: 
       ErrorCode=-2147467259
       HResult=-2147467259
       Message=Unable to connect to any of the specified MySQL hosts.
       Number=1042
       Source=MySql.Data
       StackTrace:
            at MySql.Data.MySqlClient.NativeDriver.Open()
            at MySql.Data.MySqlClient.Driver.Open()
            at MySql.Data.MySqlClient.Driver.Create(MySqlConnectionStringBuilder settings)
            at MySql.Data.MySqlClient.MySqlPool.GetPooledConnection()
            at MySql.Data.MySqlClient.MySqlPool.TryToGetDriver()
            at MySql.Data.MySqlClient.MySqlPool.GetConnection()
            at MySql.Data.MySqlClient.MySqlConnection.Open()
            at NLog.Targets.DatabaseTarget.OpenConnection(String connectionString)
            at NLog.Targets.DatabaseTarget.EnsureConnectionOpen(String connectionString)
            at NLog.Targets.DatabaseTarget.WriteEventToDatabase(LogEventInfo logEvent)
            at NLog.Targets.DatabaseTarget.Write(LogEventInfo logEvent)
            at NLog.Targets.Target.Write(AsyncLogEventInfo logEvent)
       InnerException: 
            ErrorCode=11001
            HResult=-2147467259
            Message=No such host is known
            NativeErrorCode=11001
            Source=System
            StackTrace:
                 at System.Net.Dns.GetAddrInfo(String name)
                 at System.Net.Dns.InternalGetHostByName(String hostName, Boolean includeIPv6)
                 at System.Net.Dns.GetHostEntry(String hostNameOrAddress)
                 at MySql.Data.Common.MyNetworkStream.CreateStream(MySqlConnectionStringBuilder settings, Boolean unix)
                 at MySql.Data.Common.StreamCreator.GetStream(MySqlConnectionStringBuilder settings)
                 at MySql.Data.MySqlClient.NativeDriver.Open()
            InnerException: 

I've tried changing the rules to:

  <rules>
    <logger name="NLog.*" minlevel="TRACE" writeTo="nulltarget" final="true"/>
    <logger name="MySql.*" minlevel="TRACE" writeTo="nulltarget" final="true"/>
    <logger name="System.*" minlevel="TRACE" writeTo="nulltarget" final="true"/>
    <logger name="*" levels="TRACE, DEBUG, INFO" writeTo="MySqlLogTarget"/>
    <logger name="*" levels="WARN, ERROR, FATAL" writeTo="MySqlErrorTarget"/>
    <logger name="*" minlevel="INFO" writeTo="console" />
  </rules>

However, it doesn't help. Any ideas how can I avoid the StackOverflowException?

Answer 1

Set throwExceptions on <nlog to false . The connection exception will be ignored by NLog and NLog won't try to log it to the database.

Answer 2

Turns out that somewhere in my code base was this line invoked:

Trace.Listeners.Add(new NLogTraceListener());

Which caused that error log from MySql was redirected to Trace, and thanks to the NLogTraceListener, it was logged by NLog using MySql target, which failed and was redirected to Trace, and thanks to the NLogTraceListener, it was logged by NLog using MySql target, which... you know how this goes.

I didn't come up with a nice solution since there is no enough info to filter the logs in the TraceListener (just a message as a string). Therefore I've turned off the NLogTraceListener temporarily, as it's not crucial to have it on.