1. 基于redis队列，防止高并发的超卖
2. 基于mysql的事务加排它锁，防止高并发的超卖
基于redis队列工作流程：
1. 管理员根据goods表中的库存，创建redis商品库存队列
2. 客户端访问秒杀API
3. web服务器先从redis的商品库存队列中查询剩余库存重点内容
4. redis队列中有剩余，则在mysql中创建订单，去库存，抢购成功
5. redis队列中没有剩余，则提示库存不足，抢购失败重点内容
基于mysql事务和排它锁工作流程：
1. 开启事务
2. 查询库存，并显示的设置写锁（排他锁）：SELECT * FROM goods WHERE id = 1 FOR UPDATE
3. 生成订单
4. 去库存，隐示的设置写锁（排他锁）：UPDATE goods SET counts = counts – 1 WHERE id = 1
5. commit，释放锁
注意：第二步步可以设置共享锁，不然有可能会造成死锁。
代码：
<?php /********************************************** * 抢购模块 * * @author liubin * @date 2016-02-10 * * ab -n 1000 -c 100 * */ class seckill extends common { private $_orderModel = null; private $_goodsModel = null; private $_redis = null; /* * 错误信息 */ protected $_error = ''; /** * 构造器 * */ public function __construct() { if($this->_orderModel === null){ $this->_orderModel = new OrderModel(); } if($this->_goodsModel === null){ $this->_goodsModel = new GoodsModel(); } if($this->_redis === null){ $this->_redis = new QRedis(); } } /* * 秒杀API * * @author liubin * @date 2017-02-10 */ public function addQsec(){ $gid = intval($_GET['gid']); $type = isset($_GET['type']) ? $_GET['type'] : 'mysql'; switch ($type) { case 'mysql': $this->order_check_mysql($gid); echo $this->getError(); break; case 'redis': $this->order_check_redis($gid); echo $this->getError(); break; case 'transaction': $this->order_check_transaction($gid); echo $this->getError(); break; default: echo '类型错误'; break; } } /* * 获取错误信息 * * @author liubin * @date 2017-02-10 */ public function getError(){ return $this->_error; } /* * 基于mysql验证库存信息 * @desc 高并发下会导致超卖 * * @author liubin * @date 2017-02-10 */ protected function order_check_mysql($gid){ $model = $this->_goodsModel; $pdo = $model->getHandler(); $gid = intval($gid); /* * 1：$sql_forlock如果不加事务，不加写锁： * 超卖非常严重，就不说了 * * 2：$sql_forlock如果不加事务，只加写锁： * 第一个会话读$sql_forlock时加写锁，第一个会话$sql_forlock查询结束会释放该行锁. * 第二个会话在第一个会话释放后读$sql_forlock的写锁时，会再次$sql_forlock查库存 * 导致超卖现象产生 * */ $sql_forlock = 'select * from goods where id = '.$gid .' limit 1 for update'; //$sql_forlock = 'select * from goods where id = '.$gid .' limit 1'; $result = $pdo->query($sql_forlock,PDO::FETCH_ASSOC); $goodsInfo = $result->fetch(); if($goodsInfo['counts']>0){ //去库存 $gid = $goodsInfo['id']; $sql_inventory = 'UPDATE goods SET counts = counts - 1 WHERE id = '.$gid; $result = $this->_goodsModel->exect($sql_inventory); if($result){ //创订单 $data = []; $data['order_id'] = $this->_orderModel->buildOrderNo(); $data['goods_id'] = $goodsInfo['id']; $data['addtime'] = time(); $data['uid'] = 1; $order_rs = $this->_orderModel->create_order($data); if($order_rs){ $this->_error = '购买成功'; return true; } } } $this->_error = '库存不足'; return false; } /* * 基于redis队列验证库存信息 * @desc Redis是底层是单线程的,命令执行是原子操作,包括lpush,lpop等.高并发下不会导致超卖 * * @author liubin * @date 2017-02-10 */ protected function order_check_redis($gid){ $goodsInfo = $this->_goodsModel->getGoods($gid); if(!$goodsInfo){ $this->_error = '商品不存在'; return false; } $key = 'goods_list_'.$goodsInfo['id']; $count = $this->_redis->getHandel()->lpop($key); if(!$count){ $this->_error = '库存不足'; return false; } //生成订单 $data = []; $data['order_id'] = $this->_orderModel->buildOrderNo(); $data['goods_id'] = $goodsInfo['id']; $data['addtime'] = time(); $data['uid'] = 1; $order_rs = $this->_orderModel->create_order($data); //库存减少 $gid = $goodsInfo['id']; $sql = 'UPDATE goods SET counts = counts - 1 WHERE id = '.$gid; $result = $this->_goodsModel->exect($sql); $this->_error = '购买成功'; return true; } /* * 基于mysql事务验证库存信息 * @desc 事务 和 行锁 模式,高并发下不会导致超卖，但效率会慢点 * @author liubin * @date 2017-02-10 说明： 如果$sql_forlock不加写锁，并发时，$sql_forlock查询的记录存都大于0，可以减库存操作. 如果$sql_forlock加了写锁，并发时，$sql_forlock查询是等待第一次链接释放后查询.所以库存最多就是5 */ protected function order_check_transaction($gid){ $model = $this->_goodsModel; $pdo = $model->getHandler(); $gid = intval($gid); try{ $pdo->beginTransaction();//开启事务处理 /* * 1：$sql_forlock如果只加事务，不加写锁： * 开启事务 * 因为没有加锁，读$sql_forlock后，并发时$sql_inventory之前还可以再读。 * $sql_inventory之后和commit之前才会锁定 * 出现超卖跟事务的一致性不冲突 * * * 2：$sql_forlock如果加了事务，又加读锁： * 开启事务 * 第一个会话读$sql_forlock时加读锁，并发时，第二个会话也允许获得$sql_forlock的读锁， * 但是在第一个会话执行去库存操作时（写锁），写锁便会等待第二个会话的读锁，第二个会话执行写操作时，写锁便会等待第一个会话的读锁， * 出现死锁 * 3：$sql_forlock如果加了事务，又加写锁： * 开启事务 * 第一个会话读$sql_forlock时加写锁，直到commit才会释放写锁，并发查询不会出现超卖现象。 * */ $sql_forlock = 'select * from goods where id = '.$gid .' limit 1 for update'; //$sql_forlock = 'select * from goods where id = '.$gid .' limit 1 LOCK IN SHARE MODE'; //$sql_forlock = 'select * from goods where id = '.$gid .' limit 1'; $result = $pdo->query($sql_forlock,PDO::FETCH_ASSOC); $goodsInfo = $result->fetch(); if($goodsInfo['counts']>0){ //去库存 $gid = $goodsInfo['id']; $sql_inventory = 'UPDATE goods SET counts = counts - 1 WHERE id = '.$gid; $result = $this->_goodsModel->exect($sql_inventory); if(!$result){ $pdo->rollBack(); $this->_error = '库存减少失败'; return false; } //创订单 $data = []; $data['id'] = 'null'; $data['order_id'] = $this->_orderModel->buildOrderNo(); $data['goods_id'] = $goodsInfo['id']; $data['uid'] = 'abc'; $data['addtime'] = time(); $sql = 'insert into orders (id,order_id,goods_id,uid,addtime) values ('.$data['id'].',"'.$data['order_id'].'","'.$data['goods_id'].'","'.$data['uid'].'","'.$data['addtime'].'")'; $result = $pdo->exec($sql); if(!$result){ $pdo->rollBack(); $this->_error = '订单创建失败'; return false; } $pdo->commit();//提交 $this->_error = '购买成功'; return true; }else{ $this->_error = '库存不足'; return false; } }catch(PDOException $e){ echo $e->getMessage(); $pdo->rollBack(); } } /* * 创建订单 * mysql 事物处理，也可以用存储过程 * */ private function create_order($goodsInfo){ //生成订单 $data = []; $data['order_id'] = $this->_orderModel->buildOrderNo(); $data['goods_id'] = $goodsInfo['id']; $data['addtime'] = time(); $data['uid'] = 1; $order_rs = $this->_orderModel->create_order($data); //库存减少 $gid = $goodsInfo['id']; $sql = 'UPDATE goods SET counts = counts - 1 WHERE id = '.$gid; $result = $this->_goodsModel->exect($sql); return true; } }