PHP PDO类的内存使用情况

Question

我在这里花了一些时间，我试图在自己之后进行适当的清理（;）），并显示我的类和方法正在使用多少内存。

因此，我遇到的问题是：

1. 似乎清理后，比上一次内存检查（返回前内存）使用的内存更多

这是课程，测试页面和结果（以及在线结果）

类：

<?php

class o7thDB {

public $Type =          1;          // What type of database are we connecting to
public $Host =          '';         // The host server we are connecting to
public $Name =          '';         // The name of the database
public $User =          '';         // The user to login with
public $Pass =          '';         // The password to login with
public $Query =         '';         // The query to execute
public $Params =        array();    // An array of parameters to pass to the query for execution
public $ShouldCache =   false;      // Should the results be cached?
public $CacheKey =      '';         // What should we name the key for this cache?
public $Exceptions =    '';         // Returns a string representing the exception that occurred if any
/* Memory Usage Tests */
public $InitialMemory;
public $PreSelectMemory;
public $CreatePDOMemory;
public $PostSelectMemory;
public $PreReturnMemory;

protected $DBHandle;
protected $Cache;

protected function Connect(){
    $this->InitialMemory = memory_get_peak_usage();
    if(session_status() != PHP_SESSION_ACTIVE){
        session_start();
    }
    $dsn = array();
    switch ($this->Type) {
        case 1: // MS SQL 
            $dsn = array("mssql:host=$this->Host;dbname=$this->Name", $this->User, $this->Pass);
            break;
        case 2: // MS SQL Server
            $dsn = array("sqlsrv:server=$this->Host;database=$this->Name", $this->User, $this->Pass);
            break;
        case 3: // MS Access
            $dsn = array("odbc:Driver={Microsoft Access Driver (*.mdb)};Dbq=$this->Name;Uid=$this->User");
            break;
        case 4: // Oracle
            $dsn = array("OCI:dbname=$this->Name;charset=UTF-8", $this->User, $this->Pass);
            break;
        case 5: // Informix
            $dsn = array("informix:DSN=$this->Name", $this->User, $this->Pass);
            break;
        case 6: // Firebird
            $dsn = array("firebird:dbname=$this->Host:$this->Name", $this->User, $this->Pass);
            break;
        case 7: // MySQL
            $dsn = array("mysql:host=$this->Host;dbname=$this->Name", $this->User, $this->Pass);
            break;
        case 8: // SQLLite
            $dsn = array("sqlite:$this->Host");
            break;
        default: // MySQL
            $dsn = array("mysql:host=$this->Host;dbname=$this->Name", $this->User, $this->Pass);
            break;
    }
    try{
        $this->DBHandle = new PDO($dsn[0], $dsn[1], $dsn[2]);
        $this->DBHandle->setAttribute(PDO::ATTR_PERSISTENT, true);
        $this->DBHandle->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        $this->CreatePDOMemory = memory_get_peak_usage();
    } catch (PDOException $e) {
        $this->Exceptions = $e->getMessage();
    }
}

// Destroying Everything
public function __destruct(){
    unset($this->DBHandle, $this->Cache, $this->Type, $this->Host, $this->Name, $this->User, $this->Pass, 
            $this->Query, $this->Params, $this->ShouldCache, $this->CacheKey, $this->Exceptions);
}

// Executes a query against the database, returns boolean success
public function Execute(){

}

// Executes a select statement against the database, returns an associative array
public function Select(){
    $this->Connect();
    $this->PreSelectMemory = memory_get_peak_usage();
    $stmt = $this->DBHandle->prepare($this->Query);
    $stmt->execute($this->Params);
    $ret = $stmt->fetchAll(PDO::FETCH_ASSOC);
    $this->PostSelectMemory = memory_get_peak_usage();
    if($this->ShouldCache){         
        $cKey = $this->CacheKey . session_id();
        if(isset($this->Cache[$cKey])){
            $this->PreReturnMemory = memory_get_peak_usage();
            return $this->Cache[$cKey];
        }else{
            $this->PreReturnMemory = memory_get_peak_usage();
            $this->Cache[$cKey] = $ret;
            return $ret;
        }
    }else{
        $this->PreReturnMemory = memory_get_peak_usage();
        return $ret;
    }
    $stmt->closeCursor();
    unset($stmt, $ret); 
}

}
?>

测试页：

<?php

    // Show All Errors
    error_reporting(E_ALL);
    ini_set('display_errors', '1');

    require_once($_SERVER['DOCUMENT_ROOT'] . '/Database/o7th.db.class.php');

    // Time the Execution
    $mtime = microtime(); 
    $mtime = explode(" ",$mtime); 
    $mtime = $mtime[1] + $mtime[0]; 
    $starttime = $mtime; 

    $db = new o7thDB();
    $db->Type = 7;
    $db->Host = 'localhost';
    $db->Name = 'mydb';
    $db->User = 'myun';
    $db->Pass = 'mypw'; 
    $db->Query = "Select * From `modx_session` Where `data` Like ? Or `id` Like ?";
    $db->ShouldCache = true;
    $db->CacheKey = 'a';
    $db->Params = array('%a%', '%Welcome%');
    $ret = $db->Select();   
    $rCt = count($ret);
    echo $rCt . ': Records Returned<br />'; 
    echo $db->Exceptions;
    unset($ret);

    echo $db->InitialMemory . ': Initial Memory<br />';
    echo $db->CreatePDOMemory . ': Create PDO Memory<br />';
    echo $db->PreSelectMemory . ': Pre-Select Memory<br />';
    echo $db->PostSelectMemory . ': Post-Select Memory<br />';
    echo $db->PreReturnMemory . ': Pre-Return Memory<br />';
    unset($db);

    echo memory_get_peak_usage() .': After all is said and done!<br />';

    echo '<hr />';

    $mtime = microtime(); 
    $mtime = explode(" ",$mtime); 
    $mtime = $mtime[1] + $mtime[0]; 
    $endtime = $mtime; 
    $totaltime = ($endtime - $starttime); 

    echo "This page was created in ".$totaltime." seconds"; 

?>

测试页结果：

21168: Records Returned
288016: Initial Memory
288016: Create PDO Memory
288016: Pre-Select Memory
19209456: Post-Select Memory
19209552: Pre-Return Memory
19209768: After all is said and done!
This page was created in 0.066221952438354 seconds

所以，我的问题是，为什么在清理完代码后，为什么代码占用更多的内存呢？

Answer 1

PHP进程不会释放已释放的内存。 通过释放PHP脚本中的内存，您可以将其用于同一过程。 但是整个过程始终拥有其在运行时分配的所有内存。

这就是为什么在PHP中不需要自己清理的原因-无论如何您都无法在脚本运行时将其返回给系统，但是整个运行时只需要几分之一的时间-因此，没有任何麻烦。

顺便说一句，您的班级看起来太错误了...虚构的一堂。
坦白地说，它旨在解决想象中的问题，而不是实际的问题。 像连接到所有可能的数据库。 同时，它缺少真正重要的东西。

而且基于会话的缓存机制看起来很糟糕。 确实，它将以许多无用的数据污染您的内存。

• 假设您的网站上有10个页面，并且每个页面都会保存所有其他页面的缓存数据。
• 假设一次将有10个用户浏览您的网站-因此，您将有10个相同数据的副本存储在10个不同文件中。

由于所有这些重复的 “缓存”都占用了您过于担心的内存。

结果，效果将相反-缓存并没有加快站点的速度，反而实际上使它变慢且膨胀。

这就是为什么这样说： “过早的优化是万恶之源”