CODEWITHSUNDEEP
phpmysqldatabasememoryfatal-error
Bhashithe
Bhashithe

Reputation: 122

PHP Exceeding memory while accessing database

I am developing a Object Oriented website with PHP while using some design patterns I just learnt. I have a singleton class for the Database and Some other classes which does some database operations using an instance of the Database class.

Classes,

  1. Database (singleton)
  2. User
  3. Node
  4. Sensor

class Database {
    //adaptor variable 
    private $db;

    //singleton instance
    private static $instance=NULL;

    private $config = array(
                            'host'      => 'localhost',
                            'username'  => 'XXXXXXX',
                            'password'  => '',
                            'dbname'    => 'XXX'
                            );

    private function __construct() {
        try
        {
            echo "using construct";
            //adaptor
            $this->db = new PDO('mysql:host=' . $this->config['host'] . ';dbname=' . $this->config['dbname'], $this->config['username'], $this->config['password']);
            $this->db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch (PDOException $e) {
            die($e->getMessage());
            exit();
        }
    }


    public static function getConnection()
    {
        if(self::$instance==NULL)
        {
            self::$instance = new Database();
        }
        return self::$instance;
    }

    public function prepare($sql)
    {
        return $this->db->prepare($sql);
    }
}

Other classes uses the getConnection function to get the singleton instance

class User extends Visitor {
//* has getters and setters(setters via database only)
private $db;
private $username; //*
private $email; //*
private $confirmed;//*
private $nodes;
private $id;
public function __construct() {
    $this->db = Database::getConnection();
    $argv = func_get_args();

    switch( func_num_args() ) {
        case 0: 
            self::__construct1();
            break;
        case 1:
            self::__construct2($argv[0]);
            break;
     }
}
}

So this is the basic structure of every class.

I am using singleton for the database because i don't want too many connections happening in my server which would eat up my memory.

To check whether the singleton is working properly, i have added an echo at the constructor of the database class.

So all in all, this should work properly. And it was working properly until I added some more methods to the User class(Ability to delete nodes, I have 550 lines in the user class and as I suppose, it shouldn't matter)

The error I am getting is of sort like this

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 65488 bytes) in C:\xampp\htdocs\WeatherCenter\lib\classes\Database.php on line 18

That is pointing to the config array in the database class. First I got this at my "Node" class. Then I added some

unset()

Methods into that class and then it got moved to the Database class. I am not sure why this problem is occurring, I don't have any repetitive structures in the Database class(but I have at the Node class)

ini_set('memory_limit', '-1'); is not an option since I don't want to use a way around, I need to debug the error here.

I will upload the necessary files you require,

Thanks in advance, Bhashithe

Upvotes: 1

Views: 139

Answers (2)

Bhashithe
Bhashithe

Reputation: 122

There should be a checklist for debugging things like this.

Out of memory Error or this Allowed memory exceeded error is happening due to a infinite loop or just as the error states, you are out of dedicated memory for the task and the OS terminated your process.

What I did to debug this error is go through the program line by line and check whats happening in each and every line. You might have to take notes as well. As @maxhb pointed out, the error might not point to the exact location where the bug lies, but somewhere along the path where it went and lost its memory.

In my case there was two objects calling each other in their constructors which ultimately goes on forever creating objects inside the memory until you find that you don't have enough memory.

Lessons learned:

1 You should really stick with the class diagram and create the object oriented program.

2 you should trust what your error says, they are absolutely specific most of the time

3 recursively calling each other is never a good thing

Upvotes: 0

maxhb
maxhb

Reputation: 8845

You need to find the real cause of this huge memory consumption. The line mentioned in your error message is completly misleading as most of your memory will be consumed somewhere else.

To find the critical parts of your code you could investigate memory usage by outputting something like this at appropriate places:

echo "current: " . memory_get_usage(true) . " bytes max: " . memory_get_peak_usage(true) . " bytes";

See http://php.net/manual/de/function.memory-get-usage.php

Upvotes: 1

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