When starting my Yii2/PHP application, how can I check if / wait until the database is up?
Currently with MySQL I use:
$time = time();
$ok = false;
do {
try {
$pdo = new PDO($dsn,$username,$password);
if ($pdo->query("SELECT 1 FROM INFORMATION_SCHEMA.SCHEMATA"))
$ok=true;
} catch (\Exception $e) {
sleep(1);
}
} while (!$ok && time()<$time+30);
Now I want make my application running with MySQL and PostgreSQL.
But SELECT 1 FROM INFORMATION_SCHEMA.SCHEMATA does not work in PostgreSQL.
Is there a SQL-statement (using PDO database connectivity) that works on both database systems to check if the database is up and running?
Yii2 has a property to verify if a connection exists or not, it is really not necessary to create a script for this, since this framework has an abstraction implemented for the databases it supports ($isActive property).
$isActive public read-only property Whether the DB connection is
established
public boolean getIsActive ( )
You can do the check in your default controller in the following way:
<?php
class DefaultController extends Controller
{
public function init()
{
if (!Yii::$app->db->isActive) {
// The connection does not exist.
}
parent::init();
}
}
It is not good practice to force waiting for a connection to a database unless there are very specific requirements. The availability of a connection to the database must be a mandatory requirement for an application to start and the application should not "wait" for the database to be available.
There are ways to run containers in docker in an orderly manner or with a specific requirement, this link could give you a better option instead of delegating this to the application.
You could use SELECT 1 which is standard SQL.
You can use dbfiddle to test against various servers.
The server could go away an any time so checking the error response with every query is a much better approach.
Related
I'm running a Yii2 console application which starts a websocket chat service. That all is working fine and as it's supposed to, but after some time of inactivity I get SQLSTATE[HY000]: General error: 2006 MySQL server has gone away. I tried to increase timeouts, set the user abort to false and to set PDO::ATTR_PERSISTENT => true in the PDO's constructor, but this is still happening.
Is there a way to check if a database connection is still active or if not how to reconnect to the db. Either in pure php or better with the Yii2 framework.
I had a similar problem and solved it by creating my own class for DB connection, which ensures that connection is active before actual query.
class DbConnection extends \yii\db\Connection {
private $stamp;
/**
* {#inheritdoc}
*/
public function createCommand($sql = null, $params = []) {
try {
// send ping on every 10 seconds
if ($this->stamp < time()) {
$this->stamp = time() + 10;
parent::createCommand('SELECT 1')->execute();
}
} catch (\yii\db\Exception $e) {
// if ping fail, reconnect
$this->close();
$this->open();
}
return parent::createCommand($query);
}
}
Once every 10 seconds it sends "ping" query before creating a command. If ping fails (connection was interrupted), it tries to reconnect.
This will not prevent from disconnecting, but it will automatically reconnect in case if connection was interrupted. This may be tricky if you're using transactions - if connection is interrupted in the middle of transaction, transaction will be implicitly rollback by DB, and above code will implicitly reconnect, so you don't even notice that your transaction was rollback at some point.
Also I didn't test it in master-slave configuration. But it worked perfectly fine in my case (read only connection to single server), so you may use it as a base and adjust for your needs with additional checks for transactions or master/slave connections.
Not sure about where exactly you should go for this code exactly, but the concerned code to check if the connection is active following methods in yii\db\Connection class can be used
getIsActive() : Returns a value indicating whether the DB connection
is established.
and to reconnect you can use
open() : Establishes a DB connection. It does nothing if a DB
connection has already been established.
if(Yii::$app->db->isActive === FALSE){
Yii::$app->db->open();
}
I want to implement connection pooling in Php in a similar way that works in java.
Why I need this :
Let's consider a flow
Step1: Connection To Db --- Resource Id #12
Step2: some computation... time taking .3 seconds
Step3: Query on Solr .... timing taking 2 seconds
Step4: Connection To Db --- Resource Id #12 (i am using same resource id)
Step5: Exit
Though in step4 I am using the same DB resource as of step1. However, the connection will go in the sleep state for both step2 and step3 and therefore can't be used by any other PHP process (other clients) until exit.
Solution:
use mysql_close every time after query get fired: Drawback: need to connect every time and hence time-consuming
Create a java service to handle queries (possible but too time-consuming and I am looking for other solution where I need to migrate queries )
Need to explore SQL relay like the third party but I am not sure will that be a success and not many good companies have used it
mysql_pconnect is not solving my case.
Please suggest
One way that you can apply scalability techniques to this pool model is to allow on the fly changes to your pool distribution. If you have a particular permalink that is extremely popular for some reason, you could move slaves from the primary pool to the comments pool to help it out. By isolating load, you’ve managed to give yourself more flexibility. You can add slaves to any pool, move them between pools, and in the end dial-in the performance that you need at your current traffic level.
There’s one additional benefit that you get from MySQL database pooling, which is a much higher hit rate on your query cache. MySQL (and most database systems) have a query cache built into them. This cache holds the results of recent queries. If the same query is re-executed, the cached results can be returned quickly.
If you have 20 database slaves and execute the same query twice in a row, you only have a 1/20th chance of hitting the same slave and getting a cached result. But by sending certain classes of queries to a smaller set of servers you can drastically increase the chance of a cache hit and get greater performance.
You will need to handle database pooling within your code - a natural extension of the basic load balancing code in Part 1. Let’s look at how we might extend that code to handle arbitrary database pools:
<?php
class DB {
// Configuration information:
private static $user = 'testUser';
private static $pass = 'testPass';
private static $config = array(
'write' =>
array('mysql:dbname=MyDB;host=10.1.2.3'),
'primary' =>
array('mysql:dbname=MyDB;host=10.1.2.7',
'mysql:dbname=MyDB;host=10.1.2.8',
'mysql:dbname=MyDB;host=10.1.2.9'),
'batch' =>
array('mysql:dbname=MyDB;host=10.1.2.12'),
'comments' =>
array('mysql:dbname=MyDB;host=10.1.2.27',
'mysql:dbname=MyDB;host=10.1.2.28'),
);
// Static method to return a database connection to a certain pool
public static function getConnection($pool) {
// Make a copy of the server array, to modify as we go:
$servers = self::$config[$pool];
$connection = false;
// Keep trying to make a connection:
while (!$connection && count($servers)) {
$key = array_rand($servers);
try {
$connection = new PDO($servers[$key],
self::$user, self::$pass);
} catch (PDOException $e) {}
if (!$connection) {
// Couldn’t connect to this server, so remove it:
unset($servers[$key]);
}
}
// If we never connected to any database, throw an exception:
if (!$connection) {
throw new Exception("Failed Pool: {$pool}");
}
return $connection;
}
}
// Do something Comment related
$comments = DB::getConnection('comments');
. . .
?>
I am using Zend Framework for my PHP developments and here is a small function I used to execute a query. This is not about an error. The code and everything works fine. But I want to know some concept behind this.
/**
* Get dataset by executing sql statement
*
* #param string $sql - SQL Statement to be executed
*
* #return bool
*/
public function executeQuery($sql)
{
$this->sqlStatement = $sql;
if ($this->isDebug)
{
echo $sql;
exit;
}
$objSQL = $this->objDB->getAdapter()->prepare($sql);
try
{
return $objSQL->execute();
}
catch(Exception $error)
{
$this->logMessage($error->getMessage() . " SQL : " .$sql);
return false;
}
return false;
}
Bellow are unclear areas for me.
How Zend_Db_Table_Abstract Maintain database connections?
Is it creating new connection all the time when I call this function or Does it have some connection pooling?
I didn't write any coding to open or close database connection. So will zend framework automatically close connections?
If this open and close connection works all the time if I execute this function, Is there any performance issue?
Thank you and appreciate your suggestions and opinion on this.
Creating Connection
Creating an instance of an Adapter class does not immediately connect to the RDBMS server. The Adapter saves the connection parameters, and makes the actual connection on demand, the first time you need to execute a query. This ensures that creating an Adapter object is quick and inexpensive. You can create an instance of an Adapter even if you are not certain that you need to run any database queries during the current request your application is serving.
If you need to force the Adapter to connect to the RDBMS, use the getConnection() method. This method returns an object for the connection as represented by the respective PHP database extension. For example, if you use any of the Adapter classes for PDO drivers, then getConnection() returns the PDO object, after initiating it as a live connection to the specific database.
It can be useful to force the connection if you want to catch any exceptions it throws as a result of invalid account credentials, or other failure to connect to the RDBMS server. These exceptions are not thrown until the connection is made, so it can help simplify your application code if you handle the exceptions in one place, instead of at the time of the first query against the database.
Additionally, an adapter can get serialized to store it, for example, in a session variable. This can be very useful not only for the adapter itself, but for other objects that aggregate it, like a Zend_Db_Select object. By default, adapters are allowed to be serialized, if you don't want it, you should consider passing the Zend_Db::ALLOW_SERIALIZATION option with FALSE, see the example above. To respect lazy connections principle, the adapter won't reconnect itself after being unserialized. You must then call getConnection() yourself. You can make the adapter auto-reconnect by passing the Zend_Db::AUTO_RECONNECT_ON_UNSERIALIZE with TRUE as an adapter option.
Closing a Connection
Normally it is not necessary to close a database connection. PHP automatically cleans up all resources and the end of a request. Database extensions are designed to close the connection as the reference to the resource object is cleaned up.
However, if you have a long-duration PHP script that initiates many database connections, you might need to close the connection, to avoid exhausting the capacity of your RDBMS server. You can use the Adapter's closeConnection() method to explicitly close the underlying database connection.
Since release 1.7.2, you could check you are currently connected to the RDBMS server with the method isConnected(). This means that a connection resource has been initiated and wasn't closed. This function is not currently able to test for example a server side closing of the connection. This is internally use to close the connection. It allow you to close the connection multiple times without errors. It was already the case before 1.7.2 for PDO adapters but not for the others.
More information
I have a webpage with some mysql querys,
I must start new db connection and db close after every query or its more efficiently start an only one db connection at the top of the code and close at the bottom of the script?
Thanks!
Never create a new connection for every query; it's very wasteful and will overburden your MySQL server.
Creating one connection at the top of your script is enough - all subsequent queries will use that connection until the end of the page. You can even use that connection in other scripts that are include()ed into the script with your mysql_connect() call in it.
I prefer to create some sort of class called Database of which upon creation will create a database connection using mysqli (OOP version of mysql).
This way i do not have to worry about that and i have a static class that has access to the database.
class MyAPI {
private static $database = false;
public static function GetDatabase() {
if (MyAPI::$database === false) {
MyAPI::$database = new Database(credentials can go here)
}
return MyAPI::$database;
}
}
Now your system with the includsion of your API and your database can access the database and its initialization code does not have to be peppered around your files depending on what part of the program is running and your database/connection will not be created if it is not needed (only until it is called).
Just for fun i also like to have a function in my Database class that will perform a query and return its results, this way i do not have to have the SAME while loop over and over again throughout my code depending on where i make these calls.
I also forgot to answer your question. No multiple connections! its baaaad.
Only create one connection. You don't even have to close it manually.
multiple connexion is better for security and tracking.
if you're going though a firewall between front and back there will be a timeout defined so a single connection will be a problem.
but if your web server is on the same host as mysql, a single connection will be more efficient.
HI everyone, I was just wondering what the best way to make multiple queries against tables in a mysql databases is. Should I be making a new mysqli object for every different .php page ($mysqli = new mysqli("localhost", "root", "root", "db");)?
Or is there a way to reuse this one time over all php files in my website? Any suggestions would be pretty cool
My vote would be to take an OOP approach. I would have one script that has a DB conn class in it and a method in that class to check if a connection exists and if it does returns the connection object. You could have that db class script referenced [ include_once(); ] on the pages that need to access the database. Then it would be a matter of instantiating the db object, firing the "if-exists" method and if it returns true then just utilize the existing connection within the object.
You could also take a look at utilizing persitent connections to the DB
Persistent connections
However honestly you will be better off in the long run and scalability of your application to handle the db connection management yourself rather then leaving a connection constantly open.
Here is an example of how I would structure that class:
As a note, made by #alex, the mysql_error() should not be echoed to the page in an environment where the display_errors() is set to display all warnings. (e.g error_reporting(E_WARNING);)
class dbconn {
protected $database;
function __construct(){
$this->connect();
}
protected function connect() {
$this->database = mysql_connect('host', 'user', 'pass') or die("<p>Error connecting to the database<br /><strong>" . mysql_error() ."</strong></p>" );
mysql_select_db('databasename') or die("<p>Error selecting the database<br />" . mysql_error() . "</strong></p>");
}
function __destruct(){
mysql_close($this->database);
}
function db(){
if (!isset($this->database)) {
$this->connect();
}
return $this->database;
}
}
You need to create the connection for each page, as each PHP script's lifetime is that of the request.
However, you can place the connection code in one file and then include it from all pages.
You could create a connect.php that validates it's being included by your application, and then creates a DB connection.
You could then include that file at the beginning of your application's init, or the beginning of any independent script that needs a connection =)
Depends on structure of website. If you have:
<a herf='login.php'>login</a>
<a herf='register.php'>register</a>
<a herf='about.php'>about</a>
..., then you'll have to connect in every PHP file, i.e., in login.php, in register.php and in about.php. To make it easier, I would either create config.php file which holds user/pass, or even do like Shad said.
You might also have index.php that contains something like this:
if ( !isset($_GET['module']) ) {
$_GET['module'] = 'about';
}
switch ( $_GET['module'] ) {
default:
case 'about':
include 'about.php';
break;
case 'login':
include 'login.php';
break;
case 'register':
include 'register.php';
break;
}
And HTML code:
<a herf='?module=login'>login</a>
<a herf='?module=register'>register</a>
<a herf='?module=about'>about</a>
In this case you can connect in index.php and then pass the connection to all other involved files.
The 2nd way seems to be more common to me, i.e., it feels more intuitive, more handy and that's what I always do.
I believe that in some cases it might be worthy (performance-wise) to use persistent connections and reserve/release connection when needed (either for transaction or even for single query). For example, simple system that I'm now working with takes 70ms-100ms to generate, and it takes only 40ms-50ms to do SQL queries. If using "single connection" approach, it means that connection is wasted for about 50% of time, while "reserve/release connection when needed" with persistent connections would not have such issue.
One more thing - I would advise you to create some wrapper, i.e., some DBConnection class that connects to DB in constructor and has methods like select() (returns array of data), selectValue() (returns single value, e.g., $db->selectValue('select count(*) from user') would return (int)$numberOfUsers), some exec() for inserts and updates etc.