How to show Log Message in Codeigniter?

Error Messages. These are actual errors, such as PHP errors or user errors.
Debug Messages. These are messages that assist in debugging. For example, if a class has been initialized, you could log this as debugging info.
Informational Messages. These are the lowest priority messages, simply giving information regarding some process. CodeIgniter doesn't natively generate any info messages but you may want to in your application.

/*
|--------------------------------------------------------------------------
| Error Logging Threshold
|--------------------------------------------------------------------------
| 0 = Disables logging, Error logging TURNED OFF
| 1 = Error Messages (including PHP errors)
| 2 = Debug Messages
| 3 = Informational Messages
| 4 = All Messages|
*/
$config['log_threshold'] = 2;
$config['log_path'] = '';
$config['log_date_format'] = 'Y-m-d H:i:s';

syntax : log_message($level, $message);


if ($this->db->simple_query('YOUR QUERY'))
{
echo "Success!";
}
else
{
log_message('debug', 'sql query fail in... ', false);
}

if ($some_var == "") {
log_message('error', 'Some variable did not contain a value.');
}
else {
log_message('debug', 'Some variable was correctly set');
}

log_message('info', 'The purpose of some variable is to provide some value.');

// Generates a message like: User 123 logged into the system from 127.0.0.1
$info = [
'id' => $user->id,
'ip_address' => $this->request->ip_address()
];

log_message('info', 'User {id} logged into the system from {ip_address}', $info);