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getting a php pdo connection from a mysql connect


getting a php pdo connection from a mysql connect  using -'php,mysql,pdo'

I have a legacy PHP/MySQL app that calls mysql_connect(). Tons of existing downstream code makes mysql_query() calls, either directly or through wrappers, using this connection.

For new code that I develop on the app, I would like to start using PDO.

If I make a PDO connection using the same host/user/pass/dbname credentials, might I be so lucky that under the hood, PHP will re-use the original connection? Or will PHP create two distinct connections to the server (undesirable, albeit totally understandable)?

Thanks!
    

asked Sep 30, 2015 by abhimca2006
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2 Answers

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If you are using two different APIs (i.e. mysql_* and PDO), PHP will generate two different connections.


And, as a "proof", consider this portion of code :

$db = mysql_connect('localhost', 'USER', 'PASSWORD');
$pdo = new PDO('mysql://@localhost/astralblog', 'USER', 'PASSWORD');
sleep(5);


Running this will cause two distinct connections, on the MySQL server -- which will sleep for 5 seconds :

mysql> show processlist;
+----+------------+-----------------+------------+---------+------+-------+------------------+
| Id | User       | Host            | db         | Command | Time | State | Info             |
+----+------------+-----------------+------------+---------+------+-------+------------------+
| 41 | astralblog | localhost:46551 | astralblog | Sleep   |  188 |       | NULL             |
| 42 | astralblog | localhost:46552 | astralblog | Sleep   |  188 |       | NULL             |
| 43 | astralblog | localhost       | astralblog | Query   |    0 | NULL  | show processlist |
| 64 | astralblog | localhost       | NULL       | Sleep   |    4 |       | NULL             |
| 65 | astralblog | localhost       | NULL       | Sleep   |    4 |       | NULL             |
+----+------------+-----------------+------------+---------+------+-------+------------------+
5 rows in set (0,00 sec)

(The connections in question are the two last one, which appeared when I started the PHP script, and disappeared after 5 seconds)

answered Sep 30, 2015 by patelnikul321
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Both extensions internally use EG(persistent_list) to store the persistent connection handle. But they create different hashes/keys for this list, so they can't find entries of the respective other extension.

The mysql extension creates keys of the form "mysql__..." while pdo builds "PDO:DBH:DSN=::....". The hashes are used almost like array-keys in a php script. (Over-)simplyfied example:

function pconnect($host,$user,$pass) {
  global $persistent_list;
  $hashkey = sprintf("extensionname_%s_%s_%s", $host, $user, $pass);
  if ( isset($persistent_list[$hashkey]) ) {
    // use stored connection
  }
  else {
    // create new connection
  }
}

So the answer is: No, the connections will not be shared between and re-used by the mysql extension and PDO.

answered Sep 30, 2015 by loknath.ganji

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