如何解决秒杀的性能问题和超卖的讨论 及防止按钮多次点击

update number set x=x-1 where (x -1 ) >= 0;

var nn = 0;
var tipId;
//打印小票调自动打印
function OrderbyHands() {
    nn = 10;
    if (nn === 10) {
        startPrint();
        tipId = setInterval("changebtntxt()", 1000); //每隔1秒调用一次changebtntxt()方法
    }
}
function changebtntxt() {
    if (nn > 0) {
        var vv = " 打印小票 (" + nn + ")";
        $("#btnOrderPrint").prop("disabled", "disabled"); //使按钮不能被点击
        $("#btnOrderPrint").text(vv); //更改按钮上的文字
        nn--;
    }
    if (nn === 0) {
        console.info("tipId", tipId);
        $("#btnOrderPrint").removeAttr("disabled"); //使按钮能够被点击
        $("#btnOrderPrint").text(" 打印小票 "); //更改按钮上的文字
        clearInterval(tipId); //清除循环事件
    }
    
}

function startPrint() {
    var rows = grid_order.getSelecteds();
    var OrderIds = [];
    for (var i = 0; i < rows.length; i++) {
        OrderIds.push(rows[i]["OrderId"]);
    }
    if (OrderIds.length == 0) {
        modal.dangerAlert("请选择单据！");
        return;
    }
    if (OrderIds.length > 20) {
        modal.dangerAlert("一次勾选单据不能超过20单！");
        return;
    }

    var pendingRequests = {};
    jQuery.ajaxPrefilter(function (options, originalOptions, jqXHR) {
        var key = options.url;
        console.log(key);
        if (!pendingRequests[key]) {
            pendingRequests[key] = jqXHR;
        } else {
            jqXHR.abort(); //放弃后触发的提交
            //pendingRequests[key].abort(); // 放弃先触发的提交
        }
        var complete = options.complete;
        options.complete = function (jqXHR, textStatus) {
            pendingRequests[key] = null;
            if (jQuery.isFunction(complete)) {
                complete.apply(this, arguments);
            }
        };
    });
    $.ajax({
        type: "POST",
        url: "/Print/GetOrderByHands",
        datatype: "Json",
        data: { OrderIds: OrderIds },
        success: function (data) {
            if (data.IsSuccess) {
                orderPrintbyHands(data.Data.PrintOrders);
            } else {
                modal.dangerAlert(data.Message);
            }
        },
        error: function (data) {
            modal.dangerAlert(data.responseText);
        }
    });
}

  var clicktag = 0;  //标志
    $("#paywechat").click(function () {
        debugger;
        if (clicktag == 0) {  //判断标志
            clicktag = 1;   //进行标志，防止多次点击
            $("#paywechat").prop("disabled", "disabled"); //将input元素设置为disabled
            //进行标志，防止多次点击
            //定时器
            alert(1);
            //callpay(); 
            //定时器
            //setTimeout(function() {
            //    isClick = true;
            //    $("#paywechat").removeAttr("disabled");//去除input元素的disabled属性
            //}, 5000);//5秒内不能重复点击

            //setTimeout(function() {
            //    clicktag = 0;
            //    $("#paywechat").removeAttr("disabled");//去除input元素的disabled属性
            //}, 5000);  
            setTimeout(() => {
                clicktag = 0;
                $("#paywechat").removeAttr("disabled");//去除input元素的disabled属性
            }, 5000);

        }  
    });