Hello, I am looking to design a high throughput web server(millions to billions of hits a day). Each hit is going to have to parse the http header, get information for a database, construct a response, and send out a response. I have created a server, although I don't believe I am designing it right, as it is crashing under heavy load. A simple example of my server right now is as follows:

Qt Code: 
  1. TCPInterface::TCPInterface(QObject *parent) : QTcpServer(parent)
  2. {
  3.    listen(QHostAddress::Any,80);
  4.  
  5.    connect(this, SIGNAL(toDB(QTcpSocket*)), 
  6.            App::getInstance()->getDatabase(), SLOT(fromInterface(QTcpSocket*)),
  7.            Qt::QueuedConnection);
  8.    connect(App::getInstance()->getDatabase(), SIGNAL(sendToInterface(QTcpSocket*)),
  9.            this, SLOT(fromDB(QTcpSocket*)),
  10.            Qt::QueuedConnection);
  11.  }
  12.  
  13. void TCPInterface::incomingConnection(int socket)
  14. {
  15.    QTcpSocket *s = new QTcpSocket(this);
  16.    connect(s, SIGNAL(readyRead()), this, SLOT(readClient()));
  17.    connect(s, SIGNAL(disconnected()), this, SLOT(discardClient()));
  18.    connect(s, SIGNAL(destroyed()), this, SLOT(nullSocket()));
  19.    s->setSocketDescriptor(socket);
  20. }
  21.  
  22. void TCPInterface::readClient()
  23. {
  24.    QTcpSocket* socket = (QTcpSocket*)sender();
  25.  
  26.    emit toDB(socket);
  27. }
  28.  
  29. void TCPInterface::discardClient()
  30. {
  31.    QTcpSocket* socket = qobject_cast<QTcpSocket*>(sender());
  32.    if(socket != NULL)
  33.       socket->deleteLater();
  34. }
  35.  
  36. void TCPInterface::fromDB(QTcpSocket *socket)
  37. {
  38.    QString tmp = "HTTP/1.0 200 Ok\r\n";
  39.    tmp += "Content-Type: text/html; charset=\"utf-8\"\r\n";
  40.    tmp += "\r\nTest\n";
  41.  
  42.    if(socket != NULL && socket->isWritable() && socket->isOpen() && socket->state() == QTcpSocket::ConnectedState)
  43.        socket->write(tmp.toAscii());
  44.    if(socket != NULL && socket->state() == QTcpSocket::ConnectedState)
  45.        socket->disconnectFromHost();
  46. }
  47.  
  48. void TCPInterface::nullSocket()
  49. {
  50.    QTcpSocket *socket = qobject_cast<QTcpSocket*>(sender());
  51.    if(socket != NULL)
  52.        socket = NULL;
  53. }
  54.  
  55. void DatabaseInterface::fromInterface(QTcpSocket *socket)
  56. {
  57.    emit sendToInterface(socket);
  58. }
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I am not exactly sure what my problem is, but I believe it happens when a client disconnects from the server, and I try and use a socket that no longer exists. I do have back traces printing out, however they are not always the same, here are a few I have gotten:

Qt Code: 
  1. Error: signal 11:
  2. ./SimpleTCPServer[0x401ce6]
  3. /lib64/libc.so.6[0x3c14032920]
  4. /home/root/QtSDK/Desktop/Qt/4.8.1/gcc/lib/libQtCore.so.4(_ZN9QIODevice5writeEPKcx+0x22)[0x7fac6b5a6d22]
  5. ./SimpleTCPServer[0x401fb6]
  6. /home/root/QtSDK/Desktop/Qt/4.8.1/gcc/lib/libQtCore.so.4(_ZN7QObject5eventEP6QEvent+0x38e)[0x7fac6b62cbae]
  7. /home/root/QtSDK/Desktop/Qt/4.8.1/gcc/lib/libQtCore.so.4(_ZN16QCoreApplication14notifyIntern alEP7QObjectP6QEvent+0x8c)[0x7fac6b61a30c]
  8. /home/root/QtSDK/Desktop/Qt/4.8.1/gcc/lib/libQtCore.so.4(_ZN23QCoreApplicationPrivate16sendP ostedEventsEP7QObjectiP11QThreadData+0x3d3)[0x7fac6b61ebf3]
  9. /home/root/QtSDK/Desktop/Qt/4.8.1/gcc/lib/libQtCore.so.4(+0x1c7cf3)[0x7fac6b64bcf3]
  10. /lib64/libglib-2.0.so.0(g_main_context_dispatch+0x22e)[0x3c15438f0e]
  11. /lib64/libglib-2.0.so.0[0x3c1543c938]
  12. /lib64/libglib-2.0.so.0(g_main_context_iteration+0x7a)[0x3c1543ca3a]
  13. /home/root/QtSDK/Desktop/Qt/4.8.1/gcc/lib/libQtCore.so.4(_ZN20QEventDispatcherGlib13processE ventsE6QFlagsIN10QEventLoop17ProcessEventsFlagEE+0 x73)[0x7fac6b64b833]
  14. /home/root/QtSDK/Desktop/Qt/4.8.1/gcc/lib/libQtCore.so.4(_ZN10QEventLoop13processEventsE6QFl agsINS_17ProcessEventsFlagEE+0x32)[0x7fac6b618ec2]
  15. /home/root/QtSDK/Desktop/Qt/4.8.1/gcc/lib/libQtCore.so.4(_ZN10QEventLoop4execE6QFlagsINS_17P rocessEventsFlagEE+0x164)[0x7fac6b619334]
  16. /home/root/QtSDK/Desktop/Qt/4.8.1/gcc/lib/libQtCore.so.4(_ZN16QCoreApplication4execEv+0xb9)[0x7fac6b61efc9]
  17. ./SimpleTCPServer[0x401c95]
  18. /lib64/libc.so.6(__libc_start_main+0xfd)[0x3c1401ecdd]
  19. ./SimpleTCPServer[0x401b59]
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Qt Code: 
  1. Error: signal 11:
  2. SimpleTCPServer[0x4200b6]
  3. /lib64/libc.so.6[0x3cd1232920]
  4. SimpleTCPServer[0x444a18]
  5. /root/qt-everywhere-opensource-src-4.8.1/lib/libQtCore.so.4(+0x89c5b)[0x7fd32140dc5b]
  6. /lib64/libpthread.so.0[0x3cd1a07851]
  7. /lib64/libc.so.6(clone+0x6d)[0x3cd12e76dd]
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Qt Code: 
  1. Error: signal 11:
  2. SimpleTCPServer[0x4200b6]
  3. /lib64/libc.so.6[0x3cd1232920]
  4. /root/qt-everywhere-opensource-src-4.8.1/lib/libQtNetwork.so.4(_ZNK15QAbstractSocket5stateEv+0x4)[0x7fd218e85ee4]
  5. SimpleTCPServer[0x4449fc]
  6. /root/qt-everywhere-opensource-src-4.8.1/lib/libQtCore.so.4(+0x89c5b)[0x7fd218975c5b]
  7. /lib64/libpthread.so.0[0x3cd1a07851]
  8. /lib64/libc.so.6(clone+0x6d)[0x3cd12e76dd]
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Qt Code: 
  1. Error: signal 11:
  2. SimpleTCPServer[0x4200b6]
  3. /lib64/libc.so.6[0x3cd1232920]
  4. /root/qt-everywhere-opensource-src-4.8.1/lib/libQtNetwork.so.4(+0xba512)[0x7f576d893512]
  5. /root/qt-everywhere-opensource-src-4.8.1/lib/libQtNetwork.so.4(_ZN15QAbstractSocket19setSocketDescriptorEiNS_11SocketStateE6QFlagsIN9QIODevice12OpenModeFlagEE+0xb3)[0x7f576d89fd03]
  6. SimpleTCPServer[0x429996]
  7. /root/qt-everywhere-opensource-src-4.8.1/lib/libQtNetwork.so.4(+0xcfad8)[0x7f576d8a8ad8]
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Any advice on how to redesign my server would be greatly appreciated or if you happen to know why my server is crashing.

Thank you