mysql db splits ? you'll need to be *more than fairly comfortable working with mysql at a pretty techie internals level to replicate db`s and then allow the elgg builtin logic to affect the split read/updates. it's not for the faint-hearted !

w.r.t

/*
 * Standard configuration
 *
 * You will use the same database connection for reads and writes.
 * This is the easiest configuration, and will suit 99.99% of setups. However, if you're
 * running a really popular site, you'll probably want to spread out your database connections
 * and implement database replication.  That's beyond the scope of this configuration file
 * to explain, but if you know you need it, skip past this section.
 */

//Connect to another database
$r2 =mysql_connect( $host,$user, $pass) OR die(mysql_error());
mysql_select_db($db,$r2) OR die(mysql_error()); 

//Do some sql
$sql = 'INSERT INTO ...';
$res=mysql_query($sql,$r2);

//get back to elgg database
mysql_select_db($GLOBALS['CONFIG']->dbname) OR die(mysql_error());

I would recommend a more modern API like PDO or at least Mysqli.

@DhrupDeScoop: I didn't get you. Could you please share code if you have any?

@tobi: This what i have done at the moment. but i am looking for a code which does not use core php mysql connection code.

@Steve: It would better if you please share link if you have any for a reference.

Mit

Dhrup posted some text found in the engine/settings.php file. It's not relevant to what you're trying to do.

You need to start a new MySQL connection and as Steve says, it's better to use PDO than the deprecated mysql_*() functions. You'll do something like this to connect to your database:

$db = new PDO('mysql:host=localhost;dbname=YOUR_DATABASE', 'user', 'password');

$r = $db->query('SELECT * FROM your_table');

foreach ($r as $row) {

    var_dump($row);

}

A great resource is php.net/pdo

@Mitesh:

What exactly are you trying to achieve ?

You said before " .. run two databases in ELGG. First database is default ELGG database where as second database.." 

Are these 2 databases both Elg DBs ? or different for Elgg ? The answers for you will depend on your aims.. And therefore -- maybe you're looking to use MySql replication which Elgg has catered for to some degree; or if you want to simply access anither Db - solution will be different.

So -- what are the end results you seek ?

How to add a new tabel to the existing database with all the features like comment, like and download

@Brett: This is what exactly i want to do. And it worked for me. Thanks a lot!

@Dhrup: Both are different databases. I have used PDO now and it working very fine as per my need.