搶購、秒殺是如今很常見的一個應(yīng)用場景，主要需要解決的問題有兩個：
1 高并發(fā)對數(shù)據(jù)庫產(chǎn)生的壓力
2 競爭狀態(tài)下如何解決庫存的正確減少（"超賣"問題）
對于第一個問題，已經(jīng)很容易想到用緩存來處理搶購，避免直接操作數(shù)據(jù)庫，例如使用Redis。
重點在于第二個問題
常規(guī)寫法：
查詢出對應(yīng)商品的庫存，看是否大于0，然后執(zhí)行生成訂單等操作，但是在判斷庫存是否大于0處，如果在高并發(fā)下就會有問題，導(dǎo)致庫存量出現(xiàn)負(fù)數(shù)
<?php$conn=mysql_connect("localhost","big","123456"); if(!$conn){ echo "connect failed"; exit; } mysql_select_db("big",$conn); mysql_query("set names utf8");$price=10;$user_id=1;$goods_id=1;$sku_id=11;$number=1;//生成唯一訂單function build_order_no(){ return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);}//記錄日志function insertLog($event,$type=0){ global $conn; $sql="insert into ih_log(event,type) values('$event','$type')"; mysql_query($sql,$conn); }//模擬下單操作//庫存是否大于0$sql="select number from ih_store where goods_id='$goods_id' and sku_id='$sku_id'";//解鎖 此時ih_store數(shù)據(jù)中g(shù)oods_id='$goods_id' and sku_id='$sku_id' 的數(shù)據(jù)被鎖住(注3)，其它事務(wù)必須等待此次事務(wù) 提交后才能執(zhí)行$rs=mysql_query($sql,$conn);$row=mysql_fetch_assoc($rs);if($row['number']>0){//高并發(fā)下會導(dǎo)致超賣 $order_sn=build_order_no(); //生成訂單 $sql="insert into ih_order(order_sn,user_id,goods_id,sku_id,price) values('$order_sn','$user_id','$goods_id','$sku_id','$price')"; $order_rs=mysql_query($sql,$conn); //庫存減少 $sql="update ih_store set number=number-{$number} where sku_id='$sku_id'"; $store_rs=mysql_query($sql,$conn); if(mysql_affected_rows()){ insertLog('庫存減少成功'); }else{ insertLog('庫存減少失敗'); } }else{ insertLog('庫存不夠');}?>優(yōu)化方案1：將庫存字段number字段設(shè)為unsigned，當(dāng)庫存為0時，因為字段不能為負(fù)數(shù)，將會返回false
//庫存減少$sql="update ih_store set number=number-{$number} where sku_id='$sku_id' and number>0";$store_rs=mysql_query($sql,$conn); if(mysql_affected_rows()){ insertLog('庫存減少成功');}優(yōu)化方案2：使用MySQL的事務(wù)，鎖住操作的行
<?php$conn=mysql_connect("localhost","big","123456"); if(!$conn){ echo "connect failed"; exit; } mysql_select_db("big",$conn); mysql_query("set names utf8");$price=10;$user_id=1;$goods_id=1;$sku_id=11;$number=1;//生成唯一訂單號function build_order_no(){ return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);}//記錄日志function insertLog($event,$type=0){ global $conn; $sql="insert into ih_log(event,type) values('$event','$type')"; mysql_query($sql,$conn); }//模擬下單操作//庫存是否大于0mysql_query("BEGIN"); //開始事務(wù)$sql="select number from ih_store where goods_id='$goods_id' and sku_id='$sku_id' FOR UPDATE";//此時這條記錄被鎖住,其它事務(wù)必須等待此次事務(wù)提交后才能執(zhí)行$rs=mysql_query($sql,$conn);$row=mysql_fetch_assoc($rs);if($row['number']>0){ //生成訂單 $order_sn=build_order_no(); $sql="insert into ih_order(order_sn,user_id,goods_id,sku_id,price) values('$order_sn','$user_id','$goods_id','$sku_id','$price')"; $order_rs=mysql_query($sql,$conn); //庫存減少 $sql="update ih_store set number=number-{$number} where sku_id='$sku_id'"; $store_rs=mysql_query($sql,$conn); if(mysql_affected_rows()){ insertLog('庫存減少成功'); mysql_query("COMMIT");//事務(wù)提交即解鎖 }else{ insertLog('庫存減少失敗'); }}else{ insertLog('庫存不夠'); mysql_query("ROLLBACK");}?>優(yōu)化方案3：使用非阻塞的文件排他鎖
<?php$conn=mysql_connect("localhost","root","123456"); if(!$conn){ echo "connect failed"; exit; } mysql_select_db("big-bak",$conn); mysql_query("set names utf8");$price=10;$user_id=1;$goods_id=1;$sku_id=11;$number=1;//生成唯一訂單號function build_order_no(){ return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);}//記錄日志function insertLog($event,$type=0){ global $conn; $sql="insert into ih_log(event,type) values('$event','$type')"; mysql_query($sql,$conn); }$fp = fopen("lock.txt", "w+");if(!flock($fp,LOCK_EX | LOCK_NB)){ echo "系統(tǒng)繁忙，請稍后再試"; return;}//下單$sql="select number from ih_store where goods_id='$goods_id' and sku_id='$sku_id'";$rs=mysql_query($sql,$conn);$row=mysql_fetch_assoc($rs);if($row['number']>0){//庫存是否大于0 //模擬下單操作 $order_sn=build_order_no(); $sql="insert into ih_order(order_sn,user_id,goods_id,sku_id,price) values('$order_sn','$user_id','$goods_id','$sku_id','$price')"; $order_rs=mysql_query($sql,$conn); //庫存減少 $sql="update ih_store set number=number-{$number} where sku_id='$sku_id'"; $store_rs=mysql_query($sql,$conn); if(mysql_affected_rows()){ insertLog('庫存減少成功'); flock($fp,LOCK_UN);//釋放鎖 }else{ insertLog('庫存減少失敗'); } }else{ insertLog('庫存不夠');}fclose($fp);優(yōu)化方案4：使用redis隊列，因為pop操作是原子的，即使有很多用戶同時到達(dá)，也是依次執(zhí)行，推薦使用（mysql事務(wù)在高并發(fā)下性能下降很厲害，文件鎖的方式也是）
先將商品庫存如隊列
<?php$store=1000;$redis=new Redis();$result=$redis->connect('127.0.0.1',6379);$res=$redis->llen('goods_store');echo $res;$count=$store-$res;for($i=0;$i<$count;$i++){ $redis->lpush('goods_store',1);}echo $redis->llen('goods_store');?>搶購、描述邏輯
<?php$conn=mysql_connect("localhost","big","123456"); if(!$conn){ echo "connect failed"; exit; } mysql_select_db("big",$conn); mysql_query("set names utf8");$price=10;$user_id=1;$goods_id=1;$sku_id=11;$number=1;//生成唯一訂單號function build_order_no(){ return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);}//記錄日志function insertLog($event,$type=0){ global $conn; $sql="insert into ih_log(event,type) values('$event','$type')"; mysql_query($sql,$conn); }//模擬下單操作//下單前判斷redis隊列庫存量$redis=new Redis();$result=$redis->connect('127.0.0.1',6379);$count=$redis->lpop('goods_store');if(!$count){ insertLog('error:no store redis'); return;}//生成訂單 $order_sn=build_order_no();$sql="insert into ih_order(order_sn,user_id,goods_id,sku_id,price) values('$order_sn','$user_id','$goods_id','$sku_id','$price')"; $order_rs=mysql_query($sql,$conn); //庫存減少$sql="update ih_store set number=number-{$number} where sku_id='$sku_id'";$store_rs=mysql_query($sql,$conn); if(mysql_affected_rows()){ insertLog('庫存減少成功');}else{ insertLog('庫存減少失敗');} 模擬5000高并發(fā)測試
webbench -c 5000 -t 60 http://192.168.1.198/big/index.php
ab -r -n 6000 -c 5000 http://192.168.1.198/big/index.php
上述只是簡單模擬高并發(fā)下的搶購，真實場景要比這復(fù)雜很多，很多注意的地方
如搶購頁面做成靜態(tài)的，通過ajax調(diào)用接口
再如上面的會導(dǎo)致一個用戶搶多個，思路：
需要一個排隊隊列和搶購結(jié)果隊列及庫存隊列。高并發(fā)情況，先將用戶進(jìn)入排隊隊列，用一個線程循環(huán)處理從排隊隊列取出一個用戶，判斷用戶是否已在搶購結(jié)果隊列，如果在，則已搶購，否則未搶購，庫存減1，寫數(shù)據(jù)庫，將用戶入結(jié)果隊列。
測試數(shù)據(jù)表
---- 數(shù)據(jù)庫: `big`---- ------------------------------------------------------------ 表的結(jié)構(gòu) `ih_goods`--CREATE TABLE IF NOT EXISTS `ih_goods` ( `goods_id` int(10) unsigned NOT NULL AUTO_INCREMENT, `cat_id` int(11) NOT NULL, `goods_name` varchar(255) NOT NULL, PRIMARY KEY (`goods_id`)) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=2 ;---- 轉(zhuǎn)存表中的數(shù)據(jù) `ih_goods`--INSERT INTO `ih_goods` (`goods_id`, `cat_id`, `goods_name`) VALUES(1, 0, '小米手機');-- ------------------------------------------------------------ 表的結(jié)構(gòu) `ih_log`--CREATE TABLE IF NOT EXISTS `ih_log` ( `id` int(11) NOT NULL AUTO_INCREMENT, `event` varchar(255) NOT NULL, `type` tinyint(4) NOT NULL DEFAULT '0', `addtime` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, PRIMARY KEY (`id`)) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;---- 轉(zhuǎn)存表中的數(shù)據(jù) `ih_log`---- ------------------------------------------------------------ 表的結(jié)構(gòu) `ih_order`--CREATE TABLE IF NOT EXISTS `ih_order` ( `id` int(11) NOT NULL AUTO_INCREMENT, `order_sn` char(32) NOT NULL, `user_id` int(11) NOT NULL, `status` int(11) NOT NULL DEFAULT '0', `goods_id` int(11) NOT NULL DEFAULT '0', `sku_id` int(11) NOT NULL DEFAULT '0', `price` float NOT NULL, `addtime` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='訂單表' AUTO_INCREMENT=1 ;---- 轉(zhuǎn)存表中的數(shù)據(jù) `ih_order`---- ------------------------------------------------------------ 表的結(jié)構(gòu) `ih_store`--CREATE TABLE IF NOT EXISTS `ih_store` ( `id` int(11) NOT NULL AUTO_INCREMENT, `goods_id` int(11) NOT NULL, `sku_id` int(10) unsigned NOT NULL DEFAULT '0', `number` int(10) NOT NULL DEFAULT '0', `freez` int(11) NOT NULL DEFAULT '0' COMMENT '虛擬庫存', PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='庫存' AUTO_INCREMENT=2 ;---- 轉(zhuǎn)存表中的數(shù)據(jù) `ih_store`--INSERT INTO `ih_store` (`id`, `goods_id`, `sku_id`, `number`, `freez`) VALUES(1, 1, 11, 500, 0);
以上就是小編為大家?guī)淼膒hp結(jié)合redis實現(xiàn)高并發(fā)下的搶購、秒殺功能的實例全部內(nèi)容了，希望大家多多支持武林網(wǎng)~
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