QNetworkAccessManager::put is too slow with non empty data

KoVadim

I'm writing small programm like ab to test my small rest web service. My app can produce about 200-300 request per second, but ab could about 8k-9k (on the same machine). After small investigation I found the issue - if I use empty QByteArray it works fast. Here is code:

// simplesender.h
#ifndef SIMPLESENDER_H
#define SIMPLESENDER_H
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>
#include <QQueue>

#include <QObject>

class SimpleSender : public QObject
{
    Q_OBJECT
public:
    explicit SimpleSender(QObject *parent = 0)
    {
        connect(&qnam, &QNetworkAccessManager::finished, this, &SimpleSender::slFinished);
        url = QUrl("http://localhost:8080");
        m_in_progress = 0;
        sendHttpRequest();
    }

private slots:
    void slFinished(QNetworkReply *reply)
    {
        QByteArray b = reply->readAll();
        Q_UNUSED(b);
        m_in_progress--;
        sendHttpRequest();
        reply->deleteLater();
    }

private:
    int m_in_progress;
    QUrl url;

    QNetworkAccessManager qnam;
    void sendHttpRequest()
    {
        while (m_in_progress < 10) {
            QNetworkRequest r(url);
            QByteArray bb = QByteArray("t"); // with this line 200 r/s
            //QByteArray bb; // with this line 8k r/s
            qnam.put(r, bb);

            m_in_progress++;
        }
    }

};

#endif // SIMPLESENDER_H

in main.cpp

#include <simplesender.h>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    SimpleSender hs(&a);
    return a.exec();
}

to be short:
with this code 200 r/s

QByteArray bb = QByteArray("t"); // with this line 200 r/s
qnam.put(r, bb);

with this code 8000 r/s

QByteArray bb; // with this line 8k r/s
qnam.put(r, bb);

My question is how to improve performance.

[Moved to "General and desktop" ~kshegunov]

Paul Colby

Hi @KoVadim,

Just to rule out the obvious, how sure are you that its the client code, and not the server that's slower when you set the data? ie it could be that whatever is serving http://localhost:8080 responds slower when it receives "t" instead of empty content?

Cheers.

KoVadim

@Paul-Colby
I don't think so. I tested it with ab -u put.txt -T text/plain -c 100 -n 10000 "http://localhost:8080/" where put.txt contains one char. BTW, now instead of my server I use just bare nginx with next config

dav_methods PUT;
location = / {
               echo 'ok';
}

Paul Colby

@KoVadim said in QNetworkAccessManager::put is too slow with non empty data:

I tested it with ab

Great! :)

Though to simulate what your Qt code is doing, you should be using -c 1 (your code is serialising the requests).

Out of curiosity, what order of magnitude r/s is ab reporting (with -c 1)? Of course, its would be extremely hard for any client (including Qt-based ones) to match ab performance, but interesting to know the order-of-magnitude difference.

KoVadim

test just now:
with -c1 - 7441 r/s,
with -c2 - 13564 r/s,
with -c10 - 16504 r/s