Can you still use a mysqli_result object after you have closed the mysqli connection that produced it? For instance, I am creating a PHP object with a method that opens a mysqli connection, performs a query, stores the result into a parameter, then closes the connection. Will this work or should I fetch_all() the result into an array and then close the connection?
I can find nothing in the documentation or elsewhere online that answers this question. Perhaps that is because it is mind-boggingly obvious to everyone else but it is not to me.
Yes. By default, mysqli runs queries with the option MYSQLI_STORE_RESULT, which means it copies the result set to the client (into the memory of the PHP driver). Therefore when you "fetch" from a mysqli result, you're really just looping over the result set that has already been completely fetched from the MySQL Server. And if you close the connection, the driver keeps that data.
Here's a quick code example to demonstrate:
$con = new mysqli(...);
sleep(10);
/* go run SHOW PROCESSLIST in a MySQL shell to see the connection */
$sql = "SELECT SLEEP(10) FROM test.foo ";
$result = $con->query($sql);
/* observe the query running in SHOW PROCESSLIST */
$con->close();
sleep(10);
/* now go look at SHOW PROCESSLIST to verify the connection is gone */
print_r($result->fetch_all());
/* Hey! I got the data anyway */
Related
In my php script, When I am executing query on certain PDO mysql connection, on checking mysql logs, I am not able to see the connection getting closed.
Php Code:
?php
$db = new PDO('mysql:host=HOST;dbname=DB',USER,PASSWORD);
$db->exec("SHOW TABLES");
$db = null;
?>
Mysql logs:
180312 18:31:45 9048429 Connect USER#HOST on DB
9048429 Query SHOW TABLES
Though, when I remove query, I can see the mysql connection closed on the Mysql log.
php code:
?php
$db = new PDO('mysql:host=HOST;dbname=DB',USER,PASSWORD);
$db = null;
?>
Mysql log:
180312 18:33:54 9048515 Connect USER#HOST on DB
9048515 Quit
I have to close mysql connection explicitly on my script to prevent too many connections. How can I do the same?
With the above code, Mysql connection was getting closed successfully. Its just that quitting connection was not appearing on Mysql logs.
When I checked Mysql processlist, It was verified that connection was closing successfully.
In addition to the above problem, if there are query statements to be executed using pdo, then pdo statement handler object need to be destroyed too to close mysql connection as stated in php-mysql-pdo-connection-not-closing-without-destroying-statement-handler.
As stated in the documentation: "Upon successful connection to the database, an instance of the PDO class is returned to your script. The connection remains active for the lifetime of that PDO object. To close the connection, you need to destroy the object by ensuring that all remaining references to it are deleted—you do this by assigning NULL to the variable that holds the object. If you don't do this explicitly, PHP will automatically close the connection when your script ends."
So in your case setting $db=null; should do the trick
I have just recently acquired the service side of a medium size project. The former developer has all of his functions as separate php scripts instead of classes (func1.php, func2.php, etc)... All these 'functions' make a reference to mysqli_connect via referencing the actual
'databaseonnection.php' file. This is creating a new connection every time any of the scripts run (every time I have to call a function) and I don't want to do that. I was thinking about having a persistent connection, but I'm worried about it getting out of hands as the project is growing more and more every day. So, has anyone ever encountered a similar situation? What is the best way to handle my connection to the database? Any suggestions would be greatly appreciated.
From the docs for mysql_connect. If a second call is made to mysql_connect() with the same arguments, no new link will be established, but instead, the link identifier of the already opened link will be returned.
EDIT: I'm sorry I thought you wanted connectivity help. There is no way except to move all those "functions" into one file where the connection is for them only.
I create a con.php file where my PDO connection is established then include that file anywhere you wish to use a connection Here is the base for a PDO connection:
$PDO = new PDO("mysql:host=localhost;dbname=dbname", "user_name", "password");
Here is my notes on using the PDO object to make prepared queries. There is more than you need below but good luck.
Within your PHP file that needs a connection:
1: include('con.php');
2: $datas = $PDO->prepare(SELECT * FROM table WHERE title LIKE :searchquery);
// prepare method creates and returns a PDOstatment object ( print_r($datas); ) which contains an execute() method
// PDOstatment object has its own methods ie. rowCount()
// $datas->bindValue(':search', '% . $search . %', )
// Optional - Manually bind value. see http://php.net/manual/en/pdostatement.bindparam.php
3: $datas->execute( array(':searchquery' => $searchquery . '%'));
// pass in values that need to be bound AND EXECUTE.
// There are 17 ways to "fetch" data with the PDO object.
4: $datas-fetchALL(PDO::FETCH_OBJ);
close a pdo connection by the handle:
$PDO = null;
I think you'll be much better off using PDO as opposed to the old MYSQL functions e.g. mysql_connect. It's much more robust an interface.
Below is the basic code to do this:
$db_handle = new PDO("mysql:host=".$db_host.";dbname=".$db_name.";port=".$db_port."", $db_username, $db_password, $connect_options);
where $db_handle is the PDO object representing the database connection, $db_host is your hostname [usually localhost], $db_name is the name of your database, $db_port is the database port number [usually 3306], $db_username and $db_password are your database user access credentials, and $connect_options are optional driver-specific connection options.
To enable persistent connections you need to set the driver-specific connection option for it before opening the connection: $connect_options = array(PDO::ATTR_PERSISTENT => true); then execute the earlier database connection code.
You can get more information on this from the PHP Docs here: http://www.php.net/manual/en/pdo.construct.php and http://php.net/manual/en/pdo.connections.php.
Regarding creating persistent connections, I would suggest that you close every database connection you open at the end of your script (after all your database operations of course) by nullifying your database handle: $db_handle = NULL;. You should do this whether you opened a persistent connection or not. It sounds counter-intuitive, but I believe you should free up any database resources when your script is done.
The performance disadvantages of doing this [from my experience] are neglible for most applications. This is obviously an arguable assertion and you may also find the following link helpful in further clarifying your strategy in this regard:
Persistent DB Connections - Yea or Nay?
Happy coding!
if you have very complex project and need big budget to re-design, and prefer very simple alteration then
1) stay in mysqli_connect
2) move the database connection to header of your script.
3) remove the function databse close() on that functions.
4) remove the connection link variables, it wont needed for single database.
5) close the database on end of footer.
By this way, database connection establish when starting your script and after all queries, it will be closed on footer. your server can handle the connections without closing/re-open by using keepalive method. basically default keepalive value is 30 to 90 seconds.
I m working on old existing project which uses mysql function for database operation. The existing system connects to the database, say cdcol. The connection to this database is available through site wise.
Now I want to fetch data from another database say crawlerdb, assign fetched data to an array and close connection to this database. The connection to second database is inside a function say GetAccess, and each time the extra data needed, the function is called, data fetched and connection closed to the second database.
All I want is connection to first database should be available every time.
The problem I m facing is. If i don't close connection to second database. Then mysql query used after calling the function GetAccess, still search items from second database, because the connection to second database is active. If I close the connection to second database, still the query doesnot work. Following code explains my situation.
<?php
//$conn1 is permanent connection that is used sitewise.
$conn1=mysql_connect("localhost","root","",true) or die(mysql_error());
mysql_select_db("cdcol",$conn1) or die(mysql_error());
echo "1. Current Database = ".mysql_current_db();//prints cdcol
echo "<Br> Function Returned Value = ".GetAccess();
echo "<Br>2. Current Database = ".mysql_current_db(); //In GetAccess function, which is called above if mysql_close($conn2) is used, the mysql_current_db() returns empty value.
//A FUNCTION TO GET EXTRA DATA FROM SECOND DATABASE
function GetAccess(){
$conn2=mysql_connect("localhost","root","",true) or die(mysql_error());
mysql_select_db("crawlerdb",$conn2) or die(mysql_error());
$test=mysql_query("select * from tbllensinfo",$conn2); //here i have used $conn2 as link identifier
$var= mysql_num_rows($test);
mysql_close($conn2);
return $var;
}
//FUNCTION TO IDENTIFY WHICH DATABASE IS CURRENTLY BEING USED
function mysql_current_db() {
$r = mysql_query("SELECT DATABASE()") or die(mysql_error());
return mysql_result($r,0);
}
$res=mysql_query("select * from cds"); //here link identifier $conn1 is not used, i cant change this code because there are several 100s codes, so not possible to change in all of them. Everything will work if $conn1 is used here though
echo "<br>".mysql_num_rows($res);
?>
NOTE:
The two database are hosted on same server, but database users are different, one of which have no access to other database.
So in short What I need is I need to fetch data from second database frequently while connection to first database is always available.
Any help will highly be appreciable, thanks !
Thanks
Sharmila
The mysql functions, such as mysql_query, all have an optional resource parameter identifying the database connection to use. If you omit this second parameter, the functions use the most recently opened connection. That is, they use the connection resulting from the most recent call to mysql_connect. It's considered the most recent result even if you have closed it already.
(Global variable! Let's party like it's 1999!)
If you're going to use more than one connection with mysql calls in your program, you must specify the resource parameter in all mysql_* calls in your program.
Please consider switching to PDO or mysqli. The PHP people have been trying to get rid of this mysql API for years, partly because of this problem, and mostly because it has serious insecurities.
I am rather new to the PDO library, so I apologize for my inexperience. I am writing a class that uses the PDO library to build and execute queries and return the results, no matter what they are.
Within the class, I detect whether there is an open connection to a database, and if it is the same as the one being configured, it uses this one instead. This is really easy to do using the MsSQL library as the PDO::getAttribute() function returns 'CurrentDatabase' and 'SQLServerName', so I can just apply a condition like so:
if(!empty($this->PDO)){
// Get the current connection information
$current_connection = $this->PDO->getAttribute(PDO::ATTR_SERVER_INFO);
// Return if the connection is the same
if($this->connection_parameters['hostname']==$current_connection['SQLServerName']&&$this->connection_parameters['database']==$current_connection['CurrentDatabase']){
return;
}
}
However, when it comes to MySQL, the data returned from PDO::getAttribute is completely different and I cannot seem to get the database name from the current connection.
Does any body know a function or method to get the currently connected database of a MySQL connection using the PDO library in PHP?
I order to connect to both MySQL and MsSQL, you must have 2 connections. However, changing the database on a live connection is very simple.
The following simply checks if a PDO instance already exists and whether or not it is using the required database. If so then it continues with this connection, if not it changes the database.
// Test if the PDO object already exists
if(!empty($this->PDO)){
// If connection is the same then select the database
if($this->connection_engine==$this->PDO->getAttribute(PDO::ATTR_DRIVER_NAME)){
// Get the current database in use
$database = $this->PDO->query("SELECT {$this->select_db_function}");
$database = $database->fetchAll(PDO::FETCH_NUM);
$database = $database[0][0];
// If the current database matches the new database then return
if($database==$this->connection_parameters['database']){
return;
}
}
}
I see no point in looking for the opened connection and - especially - in checking for the current database.
Why can't you just open the connection, select the database for it and then use this connection all the time throughout your class - just like everyone does?
See comments on the MySQL manual page for 'USE database'
When I open a MySQL connection in PHP with just PHP's built-in MySQL functions, I do the following:
$link = mysql_connect($servername, $username, $password);
mysql_select_db($dbname);
//queries etcetera
mysql_close($link);
When I open a connection with PDO, it looks like this:
$link = new PDO("mysql:dbname=$dbname;host=$servername",$username,$password);
//prepare statements, perform queries
Do I have to explicitly close the connection like I do with mysql_connect() and mysql_close()? If not, how does PHP know when I'm done with my connection?
TIA.
Use $link = null to let PDO know it can close the connection.
PHP: PDO Connections & Connection Management
Upon successful connection to the database, an instance of the PDO class is returned to your script. The connection remains active for the lifetime of that PDO object. To close the connection, you need to destroy the object by ensuring that all remaining references to it are deleted--you do this by assigning NULL to the variable that holds the object. If you don't do this explicitly, PHP will automatically close the connection when your script ends.
PDO does not offer such a function on its own. Connections via PDO are indirectly managed via the PDO objects refcount in PHP.
But sometimes you want to close the connection anyway, regardless of the refcount. Either because you can not control it, need it for testing purposes or similar.
You can close the Mysql connection with PDO by running a SQL query. Every user that is able to connect to the Mysql server is able to KILL at least its own thread:
/*
* Close Mysql Connection (PDO)
*/
$pdo_mysql_close = function (PDO $connection) {
$query = 'SHOW PROCESSLIST -- ' . uniqid('pdo_mysql_close ', 1);
$list = $connection->query($query)->fetchAll(PDO::FETCH_ASSOC);
foreach ($list as $thread) {
if ($thread['Info'] === $query) {
return $connection->query('KILL ' . $thread['Id']);
}
}
return false;
};
$pdo_mysql_close($conn);
Related Mysql Documentation:
13.7.5.30. SHOW PROCESSLIST Syntax
13.7.6.4. KILL Syntax
Related Stackoverflow Questions:
PHP PDO close()? (Apr 2012)
When the PHP script finishes executing, all connections are closed. Also you don't have to explicitly close your connection with mysql_close().
You can also limit your connections to within local functions. That way the connection is closed as soon as the function is completed.
Well seeing as the $link for the PDO is assigned an object, PHP would set that as null as soon as the script runs so that it's no longer an object. Therefore you could just do:
$link = new PDO("mysql:dbname=$dbname;host=$servername",$username,$password);
//prepare statements, perform queries
$link = null;
http://uk3.php.net/pdo
From what i gather i could not see anyway to close it in the php manual, and examples of scripts i quickly looked at never closed the connection in anyway from what i could see.