


Session, in computers, especially in network applications, is called a "session".
A server has relatively large traffic. Due to the needs of the program, the session expiration time is set to 3 hours, resulting in the accumulation of nearly 200,000 session files under /tmp. This in turn leads to a sharp increase in CPU usage by the kernel. Because session reading and writing involves random reading and writing of a large number of small files, and they are concentrated in one directory, iowait also increases sharply.
First consider putting the session into memory
The easiest way is to mount /tmp as a tmpfs file system, that is, in memory
The second step is to store the session in a different directory
php itself supports multi-level hashing of session
In php.ini, change
<ol class="dp-c"><li class="alt"><span><span>session.save_path = /tmp; </span></span></li></ol>
is changed to
<ol class="dp-c"><li class="alt"><span><span>session.save_path = </span><span class="string">"2;/tmp/session"</span><span> </span></span></li></ol>
means to store the session in the /tmp/session folder. And it uses 2 and hashing.
Save and exit, restart php after the third step is completed
The third step, create the session storage folder
php will not automatically go there Create these folders, but some scripts for creating the folders are provided in the source file. The following script is also easy to use
<ol class="dp-c"> <li class="alt"><span><span>I=</span><span class="string">"0 1 2 3 4 5 6 7 8 9 a b c d e f"</span><span> </span></span></li> <li> <span class="keyword">for</span><span> acm in </span><span class="vars">$I</span><span>; </span> </li> <li class="alt"> <span class="keyword">do</span><span> </span> </li> <li> <span class="keyword">for</span><span> x in </span><span class="vars">$I</span><span>; </span> </li> <li class="alt"> <span class="keyword">do</span><span> </span> </li> <li> <span class="func">mkdir</span><span> -p /tmp/session/</span><span class="vars">$acm</span><span>/</span><span class="vars">$x</span><span>; </span> </li> <li class="alt"><span>done; </span></li> <li><span>done </span></li> <li class="alt"> <span class="func">chown</span><span> -R nobody:nobody /tmp/session </span> </li> <li> <span class="func">chmod</span><span> -R 1777 /tmp/session </span> </li> </ol>
Because /tmp is used for memory, all files in it will be lost after the server is restarted, so you need to add the above script to /etc/rc.local , and should be placed before starting php
The fourth step, session recycling
The session will expire after session.gc_maxlifetime, but will not be deleted immediately , after a long time, it will cause /tmp space to occupy a lot of space. I'm too lazy to study the specific deletion algorithm. The following command can delete expired sessions. The expiration time I define here is 3 hours.
<ol class="dp-c"><li class="alt"><span><span>find /tmp/session -amin +180 -</span><span class="func">exec</span><span> rm -rf {} ; </span></span></li></ol>
Put it into cron, execute it every 10 minutes, and you’re done.
This article introduces Session hashing and expired recycling in four steps. I hope it will be helpful to you.

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

查找方法:1、用strpos(),语法“strpos("字符串值","查找子串")+1”;2、用stripos(),语法“strpos("字符串值","查找子串")+1”。因为字符串是从0开始计数的,因此两个函数获取的位置需要进行加1处理。


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