How to deal with high concurrency in php

Data security under high concurrency

We know that when multiple threads write to the same file, "thread safety" problems will occur (multiple threads run the same segment at the same time The code is thread-safe if the result of each run is the same as that of a single-thread run, and the results are the same as expected).

If it is a MySQL database, you can use its own lock mechanism to solve the problem. However, in large-scale concurrency scenarios, MySQL is not recommended. In flash sales and rush sales scenarios, the most critical issue is "over-issuance". If this aspect is not controlled carefully, it will lead to the problem that the actual orders generated are more than the pre-sale products.

Reason for over-posting: (Recommended learning: PHP programming from entry to proficiency)

Assume that in a certain rush-buying scenario, we only have 100 products, at the last moment, we have consumed 99 products, leaving only the last one. At this time, the system sent multiple concurrent requests. The product balances read in these requests were all 1, and then all passed the balance judgment, eventually leading to over-issuance.

It is worth noting: Remember to set the inventory field number field to unsigned. When the inventory is 0, because the unsigned field cannot be a negative number, false will be returned

Optimization plan

Optimization 1: Use MySQL transactions to lock the rows of operations BEGIN ; SELECT ... FOR UPDATE ; COMMIT ; ROLLBACK

<?php
	//优化方案1：使用MySQL的事务，锁住操作的行
	include(&#39;./mysql.php&#39;);
	function build_order_no(){
		return date(&#39;ymd&#39;).substr(implode(NULL, array_map(&#39;ord&#39;, str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
	}
	//记录日志
	function insertLog($event,$type=0){
		global $conn;
		$sql="insert into ih_log(event,type)
		values(&#39;$event&#39;,&#39;$type&#39;)";
		mysqli_query($conn,$sql);
	}
	
	mysqli_query($conn,"BEGIN");  //开始事务
	$sql="select number from ih_store where goods_id=&#39;$goods_id&#39; and sku_id=&#39;$sku_id&#39; FOR UPDATE";//此时这条记录被锁住,其它事务必须等待此次事务提交后才能执行
	$rs=mysqli_query($conn,$sql);
	$row=$rs->fetch_assoc();
	
	if($row[&#39;number&#39;]>0){
		//生成订单
		$order_sn=build_order_no();
		$sql="insert into ih_order(order_sn,user_id,goods_id,sku_id,price)
			values(&#39;$order_sn&#39;,&#39;$user_id&#39;,&#39;$goods_id&#39;,&#39;$sku_id&#39;,&#39;$price&#39;)";
		$order_rs=mysqli_query($conn,$sql);
		//库存减少
		$sql="update ih_store set number=number-{$number} where sku_id=&#39;$sku_id&#39;";
		$store_rs=mysqli_query($conn,$sql);
		if($store_rs){
		  echo &#39;库存减少成功&#39;;
			insertLog(&#39;库存减少成功&#39;);
			mysqli_query($conn,"COMMIT");//事务提交即解锁
		}else{
		  echo &#39;库存减少失败&#39;;
			insertLog(&#39;库存减少失败&#39;);
		}
	}else{
		echo &#39;库存不够&#39;;
		insertLog(&#39;库存不够&#39;);
		mysqli_query($conn,"ROLLBACK");
	}

Optimization 2: File lock ideas

For applications where the number of daily visits is not high or the number of concurrency is not very large, there is no problem using general file operation methods. But if the concurrency is high, when we read and write files, it is very likely that multiple processes will operate on the next file. If the access to the file is not monopolized accordingly, data loss will easily occur.

<?php
//优化方案2：使用非阻塞的文件排他锁
	include (&#39;./mysql.php&#39;);
	//生成唯一订单号
	function build_order_no(){
	  return date(&#39;ymd&#39;).substr(implode(NULL, array_map(&#39;ord&#39;, str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
	}
 
	//记录日志
	function insertLog($event,$type=0){
		global $conn;
		$sql="insert into ih_log(event,type)
		values(&#39;$event&#39;,&#39;$type&#39;)";
		mysqli_query($conn,$sql);
	}
	$fp = fopen("lock.txt", "w+");
	if(!flock($fp,LOCK_EX | LOCK_NB)){
		echo "系统繁忙，请稍后再试";
		return;
	}
 
	//下单
	$sql="select number from ih_store where goods_id=&#39;$goods_id&#39; and sku_id=&#39;$sku_id&#39;";
	$rs =  mysqli_query($conn,$sql);
	$row = $rs->fetch_assoc();
	if($row[&#39;number&#39;]>0){//库存是否大于0
		//模拟下单操作
		$order_sn=build_order_no();
		$sql="insert into ih_order(order_sn,user_id,goods_id,sku_id,price)
		values(&#39;$order_sn&#39;,&#39;$user_id&#39;,&#39;$goods_id&#39;,&#39;$sku_id&#39;,&#39;$price&#39;)";
		$order_rs =  mysqli_query($conn,$sql);
		//库存减少
		$sql="update ih_store set number=number-{$number} where sku_id=&#39;$sku_id&#39;";
		$store_rs =  mysqli_query($conn,$sql);
		if($store_rs){
			echo &#39;库存减少成功&#39;;
			insertLog(&#39;库存减少成功&#39;);
			flock($fp,LOCK_UN);//释放锁
		}else{
			echo &#39;库存减少失败&#39;;
			insertLog(&#39;库存减少失败&#39;);
		}
	}else{
		echo &#39;库存不够&#39;;
		insertLog(&#39;库存不够&#39;);
	}
	
	fclose($fp);

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