mysql_close

omega99999 at gmail dot com (2011-02-20 13:44:34)

The variable is definitely not optional in 5.3... Caused me a bit of a headache when I was debugging until I realized it was the close function that was causing a hang. So if using just:

<?php
mysql_connect(<...>);

mysql_close();
?>

Use:

<?php
$connection = mysql_connect(<...>);

mysql_close($connection);
?>

(where $connection is any variable of your choice)

mdes[SPAM]saintes at gmail dot com (2010-07-09 09:12:05)

i just came over a problem that i had with apache.
It crashs and said :
"Parent: child process exited with status 3221225477 -- Restarting."
the error came from the extesion php_mysql.dll
i didn't understand what was the reason of that crash..
Then, i debug the script that i had downloaded and i noticed that that was the function mysql_close() which caused the problem.
The solution is, to send to it the link identifier which is optionnal in the description but cause a crash with no commentary.
Thanks to agneady.

Anonymous (2010-04-23 14:26:59)

At least with PHP5.3.2 and Windows connecting by tcp, you should always use this mysql_close() function to close and free up the tcp socket being used by PHP. Garbage collection after script execution does not close the tcp socket on its own. The socket would otherwise remain in 'wait' state for approximately 30 seconds, and any additional page loads/connection attempts would only add to the total number of open tcp connections. This wait time does not appear to be configurable via PHP settings.

agneady (nospam please) at gmail dot com (2009-10-11 02:09:30)

It seems that as of PHP 5.3, the link_identifier parameter is no longer optional. If not included, it would cause the script to crash with no errors in the output.

bbodelcampo at yahoo dot co dot uk (2005-12-13 05:20:18)

A little note about multiple simultaneous connections to different hosts...

I work on a site that pulls content primarily from one db but uses a db on a foreign server to verify licensing.  One might expect the following to work:

<?php
// Open the connection to the primary db
$res1 = mysql_connect($host1, $user1, $pass1);
mysql_select_db($db1);

// Open connection to the license server
$res2 = mysql_connect($host2, $user2, $pass2);
mysql_select_db($db2, $res2);

// Pull license data and close when done
mysql_query($check_sql, $res2);
// ...
mysql_close($res2);

// Now pull content from the primary db
// Not specifying the resource should default to the last open db
mysql_query($query); 
// ...
?>

Turns out this last query, since it cant find an active connection, will try to connect with mysql_connect() with no paramaters.  But if instead you do it as mysql_query($query, $res1), or alternatively, run the mysql_connect for this host again then it works fine.  Thus, it doesnt seem to be possible to have code with an overarching "global" db connection interspersed with temporary connections to another host/db....

levi at alliancesoftware dot com dot au (2005-04-29 00:03:34)

As at 5.0.x and 4.3.x: This function should never be used with shared links; instead you should set your link variables to null.
(This explains red's and beer's () problems in previous comments)

  Here is how shared links work:
  - Each link is a resource. mysql_connect() by default looks for a resource with the same paramaters. If one exists, it will return the existing resource. 
  - Every assignment of that resource to a variable increases the resource's reference count.
  - When the reference is decremented to zero, the underlying TCP/socket connection is closed.
    - Every assignment of a variable away from that resource decrements the reference count. (This includes a function level variable going out of scope)
    - mysql_close() also decrements the reference count.

Note the last two points: mysql_close() _and_ reassignment of a variable decrement the link's reference count.

A common mistake is a function like:

<?php
function dothings() {
  $link = mysql_open(...);
  // .. do some queries ..
  mysql_close($link)
  $link = null;
}
?>

this will decrement the counter twice, possibly closing the underlying connection and causing errors in other parts of the program.

http://bugs.php.net/bug.php?id=30525 "this is not a bug but just how it works"

beer_nomaed _AT_ hotmail _DOT_ com (2004-12-03 01:26:14)

Be careful when using multiple links to connect to same database (with same username). Unless you specify explicitly in mysql_connect() to create a new link, it will return an already open link. If that would be closed by mysql_close(), it will also (obviously) close the other connection, since the link is the same.
Had lot of trouble figuring it out, since in <=4.3.6 there was a bug which didn't close the connection, but after the patch to >=4.3.7, all my application broke down because of a single script that did this.