推荐学习：《PHP教程》
商城系统中，抢购和秒杀是很常见的营销场景，在一定时间内有大量的用户访问商场下单，主要需要解决的问题有两个：
高并发对数据库产生的压力；
竞争状态下如何解决商品库存超卖；
高并发对数据库产生的压力
对于第一个问题，使用缓存来处理，避免直接操作数据库，例如使用 Redis。
竞争状态下如何解决商品库存超卖
对于第二个问题，需要重点说明。
常规写法：查询出对应商品的库存，判断库存数量否大于 0，然后执行生成订单等操作，但是在判断库存是否大于 0 处，如果在高并发下就会有问题，导致库存量出现负数。
测试表 sql
把如下表数据导入到数据库中
/*Navicat MySQL Data TransferSource Server : 01 本地localhostSource Server Version : 50553Source Host : localhost:3306Source Database : testTarget Server Type : MYSQLTarget Server Version : 50553File Encoding : 65001Date: 2020-11-06 14:31:35*/SET FOREIGN_KEY_CHECKS=0;-- ------------------------------ Table structure for products-- ----------------------------DROP TABLE IF EXISTS `products`;CREATE TABLE `products` ( `id` int(10) NOT NULL AUTO_INCREMENT COMMENT "ID", `title` varchar(50) DEFAULT NULL COMMENT "货品名称", `store` int(11) DEFAULT "0" COMMENT "货品库存", PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COMMENT="货品表";-- ------------------------------ Records of products-- ----------------------------INSERT INTO `products` VALUES ("1", "稻花香大米", "20");-- ------------------------------ Table structure for order_log-- ----------------------------DROP TABLE IF EXISTS `order_log`;CREATE TABLE `order_log` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `content` varchar(255) CHARACTER SET utf8mb4 DEFAULT NULL COMMENT "日志内容", `c_time` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT "创建时间", PRIMARY KEY (`id`)) ENGINE=MyISAM DEFAULT CHARSET=latin1;-- ------------------------------ Table structure for order-- ----------------------------DROP TABLE IF EXISTS `order`;CREATE TABLE `order` ( `oid` bigint(20) unsigned NOT NULL DEFAULT "0" COMMENT "订单号", `product_id` int(11) DEFAULT "0" COMMENT "商品ID", `number` int(11) DEFAULT "0" COMMENT "购买数量", `c_time` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT "创建时间", PRIMARY KEY (`oid`)) ENGINE=MyISAM DEFAULT CHARSET=latin1 COMMENT="订单表";下单处理代码
0) { sleep(1); //step4 更新商品库存数量（减去下单数量） $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "更新成功"; //step5 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog("库存减少成功，下单成功"); } else { echo "更新失败"; insertLog("库存减少失败"); }} else { echo "没有库存"; insertLog("库存不够");}function db(){ global $con; $con = new mysqli("localhost","root","root","test"); if (!$con) { echo "数据库连接失败"; }}/** * 生成唯一订单号 */function build_order_no(){ return date("Ymd") . str_pad(mt_rand(1, 99999), 5, "0", STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values("$oid", "$product_id", "$number")"; mysqli_query($con, $sql);}/** * 记录日志 */function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values("$content")"; mysqli_query($con, $sql);}将库存字段字段设为 unsigned
因为库存字段不能为负数，在下单后更新商品库存时，如果出现负数将返回 false
0) { sleep(1); //step4 更新商品库存数量（减去下单数量） $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "更新成功"; //step5 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog("库存减少成功，下单成功"); } else { // 如果出现负数将返回false echo "更新失败"; insertLog("库存减少失败"); }} else { //商品已经抢购完 echo "没有库存"; insertLog("库存不够");}function db(){ global $con; $con = new mysqli("localhost","root","root","test"); if (!$con) { echo "数据库连接失败"; }}/** * 生成唯一订单号 */function build_order_no(){ return date("Ymd") . str_pad(mt_rand(1, 99999), 5, "0", STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values("$oid", "$product_id", "$number")"; mysqli_query($con, $sql);}/** * 记录日志 */function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values("$content")"; mysqli_query($con, $sql);}使用 mysql 的事务，锁住操作的行
在下单处理过程中，使用 mysql 的事务将正在下单商品行数据锁定
0) { sleep(1); //step4 更新商品库存数量（减去下单数量） $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "更新成功"; //step5 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog("库存减少成功，下单成功"); mysqli_query($con, "COMMIT");//事务提交即解锁 } else { echo "更新失败"; insertLog("库存减少失败"); mysqli_query($con, "ROLLBACK");//事务回滚即解锁 }} else { //商品已经抢购完 echo "没有库存"; insertLog("库存不够"); mysqli_query($con, "ROLLBACK");//事务回滚即解锁}function db(){ global $con; $con = new mysqli("localhost","root","root","test"); if (!$con) { echo "数据库连接失败"; }}/** * 生成唯一订单号 */function build_order_no(){ return date("Ymd") . str_pad(mt_rand(1, 99999), 5, "0", STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values("$oid", "$product_id", "$number")"; mysqli_query($con, $sql);}/** * 记录日志 */function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values("$content")"; mysqli_query($con, $sql);}使用非阻塞的文件排他锁
在处理下单请求的时候，用 flock 锁定一个文件，如果锁定失败说明有其他订单正在处理，此时要么等待要么直接提示用户” 服务器繁忙”，计数器存储抢购的商品数量，避免查询数据库。
阻塞 (等待) 模式：并发时，当有第二个用户请求时，会等待第一个用户请求完成、释放锁，获得文件锁之后，程序才会继续运行下去。
0) { //处理订单 sleep(1); //step4 更新商品库存数量（减去下单数量） $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "更新成功"; //step5 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog("库存减少成功，下单成功"); } else { echo "更新失败"; insertLog("库存减少失败"); } } else { //商品已经抢购完 echo "没有库存"; insertLog("库存不够"); } flock($fp, LOCK_UN); //释放锁}fclose($fp);function db(){ global $con; $con = new mysqli("localhost","root","root","test"); if (!$con) { echo "数据库连接失败"; }}/** * 生成唯一订单号 */function build_order_no(){ return date("Ymd") . str_pad(mt_rand(1, 99999), 5, "0", STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values("$oid", "$product_id", "$number")"; mysqli_query($con, $sql);}/** * 记录日志 */function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values("$content")"; mysqli_query($con, $sql);}非阻塞模式：并发时，第一个用户请求，拿得文件锁之后。后面请求的用户直接返回系统繁忙，请稍后再试
0) { //处理订单 sleep(1); //step4 更新商品库存数量（减去下单数量） $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "更新成功"; //step5 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog("库存减少成功，下单成功"); } else { echo "更新失败"; insertLog("库存减少失败"); } } else { //商品已经抢购完 echo "没有库存"; insertLog("库存不够"); } flock($fp, LOCK_UN); //释放锁} else { //系统繁忙，请稍后再试 echo "系统繁忙，请稍后再试"; insertLog("系统繁忙，请稍后再试");}fclose($fp);function db(){ global $con; $con = new mysqli("localhost","root","root","test"); if (!$con) { echo "数据库连接失败"; }}/** * 生成唯一订单号 */function build_order_no(){ return date("Ymd") . str_pad(mt_rand(1, 99999), 5, "0", STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values("$oid", "$product_id", "$number")"; mysqli_query($con, $sql);}/** * 记录日志 */function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values("$content")"; mysqli_query($con, $sql);}因为 pop 操作是原子的，即使有很多用户同时到达，也是依次执行，推荐使用
mysql 事务在高并发下性能下降很厉害，文件锁的方式也是
先将商品库存到 redis 队列
connect("127.0.0.1", 6379);$key = "goods_store_" . $product_id;$res = $redis->llen($key);$count = $store - $res;for ($i=0; $i<$count; $i++) { $redis->lpush($key, 1);}echo $redis->llen($key);function db(){ global $con; $con = new mysqli("localhost","root","root","test"); if (!$con) { echo "数据库连接失败"; }}2. 抢购、秒杀逻辑
connect("127.0.0.1",6379);$count = $redis->lpop("goods_store_" . $product_id);if (!$count) { insertLog("error:no store redis"); return "秒杀结束，没有商品库存了";}sleep(1);//step3 更新商品库存数量（减去下单数量）$sql = "update products set store=store-{$buy_num} where id={$product_id}";if (mysqli_query($con, $sql)) { echo "更新成功"; //step4 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog("库存减少成功，下单成功");} else { echo "更新失败"; insertLog("库存减少失败");}function db(){ global $con; $con = new mysqli("localhost","root","root","test"); if (!$con) { echo "数据库连接失败"; }}/** * 生成唯一订单号 */function build_order_no(){ return date("Ymd") . str_pad(mt_rand(1, 99999), 5, "0", STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values("$oid", "$product_id", "$number")"; mysqli_query($con, $sql);}/** * 记录日志 */function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values("$content")"; mysqli_query($con, $sql);}redis 乐观锁防止超卖
connect("127.0.0.1", 6379);$redis->watch("sales");//乐观锁 监视作用 set() 初始值0$sales = $redis->get("sales");$n = 20;// 库存if ($sales >= $n) { exit("秒杀结束");}//redis开启事务$redis->multi();$redis->incr("sales"); //将 key 中储存的数字值增一 ,如果 key 不存在，那么 key 的值会先被初始化为 0 ，然后再执行 INCR 操作。$res = $redis->exec(); //成功1 失败0if ($res) { //秒杀成功 $con = new mysqli("localhost","root","root","test"); if (!$con) { echo "数据库连接失败"; } $product_id = 1;// 商品ID $buy_num = 1;// 购买数量 sleep(1); $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "秒杀完成"; }} else { exit("抢购失败");}推荐学习：《PHP视频教程》
以上就是PHP高并发实例详解之解决商品库存超卖问题的详细内容，更多请关注php中文网其它相关文章！
