So in the interest of not repeating myself, I only want to create one PDO connection and pass it between pages using a session var. But when I setup my PDO connection and set the session var, the var is coming back as not set on my next page?
This is the code on my first page:
session_start();
try
{
$db = new PDO("mysql:host=".$dbHostname.";dbname=".$dbDatabase, $dbUsername, $dbPassword);
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
catch(PDOException $e)
{
echo "It seems there was an error. Please refresh your browser and try again. ".$e->getMessage();
}
$_SESSION['db'] = $db;
Then this test code on my next page comes back as not set.
session_start();
$db = $_SESSION['db'];
if(isset($db))echo "set";
else echo "not set";
Any ideas??
The connection is fine because if I call a function from the first page and pass along $db as a parameter, the function works without any problems. So why would storing the database var as a session not work? Thank you for any help.
PDO does not allow session serialization. In fact, you should not be able to serialize database connections in the session at all. If it's really necessary to do that, you can do something like this:
class DB {
private $db;
private $creds;
public function __construct($host, $dbname, $user, $pass) {
$this->creds = compact('host', 'dbname', 'user', 'pass');
$this->db = self::createLink($host, $dbname, $user, $pass);
}
public function __sleep() {
return array('creds');
}
public function __wakeup() {
$this->db = self::createLink($this->creds['host'] ...
}
public static function createLink($host ...
return new PDO(...
}
}
PHP closes database connection and free the used resources after the page finishes execution.
Secondly, it's a resource/handler and not really a value.
You can use persistent connections.
$dbh = new PDO('mysql:host=localhost;dbname=test', $user, $pass, array(
PDO::ATTR_PERSISTENT => true
));
Your application will behave exactly as if the connection was being reconstructed. So no need for you to serialize the connection and pass it around.
But you do need to be careful and close it when the user session is over so it can be released.
What exactly is your need for persistent connections?
You can use a persistent connection, but it is a bad idea. It ties up valuable system resources, might actually get you kicked off of a shared host, and is actually not all that useful. Just close the connection at the end of each page and start a new one at the next page. If you really, really want it then the setting for persistent connections is PDO::ATTR_PERSISTENT which must be set to true on your PDO object.
Related
I've been struggling with this for quite a while, and it's to the point where I need to ask for help because even with all the research I've done I can't get a handle on why this is happening.
Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000] [1040] Too many connections'
This happens upon loading a single page (index.php), and I am the only user (dev). As you can see here, the MySQL connection limit is set # 50 but I am narrowly surpassing that. This is an improvement over the 100~ connections that were being created before I refactored the code.
Here are the stats after the page has loaded once.
I've narrowed the issue down to several causes:
I don't fully understand how PDO/MySQL connections work.
I am creating too many connections in my code even though I am trying to only create one that I can share.
I need to increase the connection limit (seems unlikely).
Most of the SO questions I've found, tell the OP to increase the connection limit without truly knowing if that's the best solution so I'm trying to avoid that here if it's not needed. 50 connections for one page load seems like way too many.
These are the classes I am instantiating on the page in question.
$DataAccess = new \App\Utility\DataAccess();
$DataCopyController = new App\Controllers\DataCopyController($DataAccess);
$DriveController = new App\Controllers\DriveController($DataAccess);
$Helper = new App\Utility\Helper();
$View = new App\Views\View();
I am creating the DAL object then injecting it into the classes that need it. By doing it this way I was hoping to only create one object and one connection, however this is not what's happening obviously. Inside the DAL class I've also added $this->DbConnect->close() to each and every query method.
Here is the constructor for the DataAccess() class.
public function __construct() {
$this->DbConnect = new \App\Services\DbConnect();
$this->db = $this->DbConnect->connect("read");
$this->dbmod = $this->DbConnect->connect("write");
$this->Helper = new Helper();
}
Here is the DbConnect() class.
class DbConnect {
private $db;
private $dbmod;
private function isConnected($connection) {
return ($connection) ? TRUE : FALSE;
}
public function connect($access) {
$options = [
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
PDO::ATTR_EMULATE_PREPARES => false
];
if ($access == "read") {
if ($this->isConnected($this->db)) {
return $this->db;
} else {
if (strpos($_SERVER['SERVER_NAME'], DBNAME_DEV) === false) {
$this->db = new PDO("mysql:host=127.0.0.1; dbname=".DBNAME,
DBUSER,
DBPASS,
$options
);
} else {
$this->db = new PDO("mysql:host=" . DBHOST_DEV ."; dbname=".DBNAME_DEV,
DBUSER,
DBPASS,
$options
);
}
return $this->db;
}
} elseif ($access == "write") {
if ($this->isConnected($this->dbmod)) {
return $this->dbmod;
} else {
if (strpos($_SERVER['SERVER_NAME'], DBNAME_DEV) === false) {
$this->dbmod = new PDO("mysql:host=127.0.0.1; dbname=".DBNAME,
DBUSER_MOD,
DBPASS,
$options
);
} else {
$this->dbmod = new PDO("mysql:host=" . DBHOST_DEV . "; dbname=".DBNAME_DEV,
DBUSER_MOD,
DBPASS,
$options
);
}
}
return $this->dbmod;
}
}
public function close() {
$this->db = null;
$this->dbmod = null;
}
}
I've also tried instantiating the DbConnect() class on index.php and injecting that rather than DataAccess() but the result was the same.
EDIT:
I also want to add that this MySQL server has two databases, prod and dev. I suppose the connection limit is shared between both. However, the prod database gets very little traffic and I am not seeing this error there. When I refreshed the stats, there were no connections to the prod database.
From the PHP manual ~ http://php.net/manual/en/pdo.connections.php
Many web applications will benefit from making persistent connections to database servers. Persistent connections are not closed at the end of the script, but are cached and re-used when another script requests a connection using the same credentials.
So I would advise removing the DbConnection#close() method as you would not want to ever call this.
Also from the manual...
Note:
If you wish to use persistent connections, you must set PDO::ATTR_PERSISTENT in the array of driver options passed to the PDO constructor. If setting this attribute with PDO::setAttribute() after instantiation of the object, the driver will not use persistent connections.
So you'll want (at least)
new \PDO("mysql:host=127.0.0.1;dbname=" . DBNAME, DBUSER, DBPASS, [
PDO::ATTR_PERSISTENT => true
]);
You can also set your other connection attributes in the constructor.
I had a problem, which I solved but I don't fully understand why the solution works:
Without the '$conn = null;' statement in the code below the number of database connections was increasing and I got a "too many database connections" error. With that statement it works fine - no increasing nr of dbase connections, but I would have assumed that the '$conn = new Database($dbname[$day]);' statement would set a new database connection, and therefore automatically close the previous one. Obvious not, but why?
for($day=0;$day<365;$day++){
//code to determine $dbname here...
$conn = new Database($dbname[$day]); //Database() is defined class
//code to access database $dbname
$conn = null; //close connection
}//for
UPDATE: the the constructor for the Database class as requested:
public function __construct($dbname) {
try {
if($dbname != ECIS_DB_NAME){ //access to master database is forbidden
$this->_db = new PDO('mysql:host='.ECIS_DB_HOST.';dbname='.$dbname, ECIS_DB_USER, ECIS_DB_PASS, array(
PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => true
));
$this->_db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$this->_db->query('SET CHARACTER SET utf8');
self::$count++;
}//if
} catch (PDOException $e) {
exit('Error while connecting to database.'.$e->getMessage());
}
}//public function __construct
By unassigning $conn you are removing all references to the class and its __destruct method should be called. See "Is destructor in PHP predictable?".
The __destruct method likely has code to close the database connection. However, you should explicitly close the connection if possible, e.g.
$conn->close();
$conn = null;
If you are only connecting to a single database outside of your tests, you should initialize the database connection outside of your forloop.
I am thinking, is it safe and OK to use db connection in function to return it anywhere in the project? If I want to reuse this project to build another one, I can change db connection only in this function and I don't need to go all over the script searching and changing connection parameter.
function connect_db(){
$db = new PDO('mysql:host=localhost;dbname=;charset=utf8', '', '');
return $db;
}
Now I can call it anywhere functions.php file is required once, by returning
$db = connect_db();
and then whatever statement follows.
Is it ok and safe?
And how to close connection like this at the end of the page?
$db = NULL;
apparently won't work.
Yes, it is safe and ok to have a single place that creates a connection to your database. I would change your function just a bit though:
<?php
function connect_db(){
try{
return new PDO('mysql:host=localhost;dbname=mydb', 'username', 'password', array(PDO::MYSQL_ATTR_INIT_COMMAND =>'SET NAMES utf8'));
}catch (PDOException $e){
echo '<p>Error connecting to database! ' . $e->getMessage() . '</p>';
die();
}
}
?>
You can read more about the PDO constructor in the documentation.
And to close the PDO connection created this way you do indeed just:
<?php
$pdo = NULL;
?>
Please note that there is really a lot more to be said on this subject. Ideally you would have a class that handles the creation of your PDO object(s). You might want to take a look at this excellent answer from Gordon as a place to start.
There is something, as a newbie, that a I want to understand about About database connections.
I am starting off from a tutorial on PHP which has this structure:
Connect.php:
<?php
$username = "dbusername";
$password = "dbpassword";
$host = "localhost";
$dbname = "dbname";
$options = array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8');
try
{
$db = new PDO("mysql:host={$host};dbname={$dbname};charset=utf8", $username, $password, $options);
}
catch(PDOException $ex)
{
die("Failed to connect to the database: " . $ex->getMessage());
}
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
header('Content-Type: text/html; charset=utf-8');
session_start();
?>
Login.php:
<?php
require("connect.php");
// some code not important for this question,
//that handles login with a session…
?>
various_file_in_the_login_system.php:
<?php
require("connect.php");
// some code that checks if user is logged in with session_ …
// some code that does need the database connection to work
?>
All other files also contain that require("connect.php"); line. It works, but I just don’t know what these connection request to the server – I may not be using the right vocabulary -- end up doing to the server. They are superfluous if the connection is not timed out, are they not?
I found a post which talked about doing a singleton for PDO, and a post which makes me feel like never using persistent connections in my life.
Does this design causes excessive connection churning?
Perhaps servers can handle very many request for connection per second, perhaps a server has its own internal persistent connection mode, or implements connection pooling…
Or the PDO object handle the problem of asking connection too often for no reason…
PDO + Singleton : Why using it?
What are the disadvantages of using persistent connection in PDO
This is what I can recommend for your database connection:
Make a class for the connection:
class Database{
private static $link = null ;
public static function getConnection ( ) {
if (self :: $link) {
return self :: $link;
}
$dsn = "mysql:dbname=social_network;host=localhost";
$user = "user";
$password = "pass";
self :: $link = new PDO($dsn, $user, $password);
return self :: $link;
}
}
Then you can get the connection like this:
Database::getConnection();
The Singleton Pattern is hard to scale - However, I think it will probably be fine for your needs. It takes a lot of load off your database.
I don't think you will be able to avoid the multiple includes.
There is a php.ini setting for prepending a file to every script -> http://www.php.net/manual/en/ini.core.php#ini.auto-prepend-file
How about you change to
require_once('connect.php');
in all locations?
Also you should probably remove session_start() and HTTP header logic from a section of code that has to do with establishing a DB connection. This simply does not make sense there.
I have, what I think/hope, is a very simple PHP question. I have made a class to create database connections and issue common queries. I am trying to open two different database connections by creating two objects from the same database class. My code is as follows:
//connect to DB
$dbh = new DB('localhost', 'db1', 'user', 'pass');
//check connection
if(!$dbh->getStatus()) {
echo($dbh->getErrorMsg());
die;
}//if
//connect to DB 2
$dbh2 = new DB('localhost', 'db2', 'user', 'pass');
//check connection
if(!$dbh2->getStatus()) {
echo($dbh2->getErrorMsg());
die;
}//if
However, when I call a method for $dbh to query the database, it attempts to query with the credentials for $dbh2.
My DB constructor is below:
class DB {
function __construct($host, $db, $user, $pass) {
$dbh = mysql_connect($host, $user, $pass);
mysql_select_db($db, $dbh);
if(!$dbh) {
$this->status = false;
$this->error_msg = 'Error connecting to database: '.mysql_error();
return(false);
}//if
$this->dbh = $dbh;
$this->resetStatusAndErrors();
return($dbh);
}//_construct
Simple solution: Use PDO instead. It does exactly what you want, probably has better syntax and implementation and abstracts the interface for DB access.
You're not showing the full class, but the most probable reason is that you are not passing the current connection to the mysql_query() command.
Save $dbh as a property of your class, and add the connection parameter to each mysql_ function that accepts it:
mysql_query("SELECT * from.......", $this->dbh);
That said, if you are building this from scratch at the moment, take a look whether you don't want to use PDO instead. It is better, safer and more flexible than the old style mySQL library.
If you are using the mysql extension (using either mysqli or PDO_MySQL would give both superior performance, more features, etc., so check that for new code), you'll have to store the database handle, and use that on every mysql_* call:
class db {
....
function query($query){
return mysql_query($query, $this->dbh);//notice the second parameter.
}
}