Scaling issue at high connection count with journal enabled under WiredTiger

function conns() {

    return db.serverStatus().connections.current

}

function ops() {

    return db.serverStatus().opcounters.insert

}

function repro(threads_insert) {

    // run forever

    seconds = 10000

    // starting stats

    last_conns = curr_conns = start_conns = conns()

    last_time = new Date()

    last_ops = ops()

    // loop starting new connections

    while (curr_conns < start_conns+threads_insert) {

        // start 10 more insert threads with a random delay around 100ms (10 inserts/second/thread)

        res = benchStart({

            ops: [{

                op: "insert",

                ns: "test.c",

                doc: {},

                delay: NumberInt(100 + Math.random()*10-5)

            }]

            seconds: seconds,

            parallel: 10,

        })

        // 10 new connections every 100ms

        sleep(100)

        // print op rate vs connections

        curr_conns = conns()

        if (curr_conns-last_conns >= 100) {

            curr_time = new Date()

            curr_ops = ops()

            ops_per_sec = Math.round((curr_ops - last_ops) / ((curr_time - last_time) / 1000.0))

            avg_conns = (last_conns+curr_conns) / 2

            print('' + avg_conns + '\t' + ops_per_sec)

            last_time = curr_time

            last_ops = curr_ops

            last_conns = curr_conns

        }

    }

    // run forever

    sleep(seconds*1000)

}