Mage registry key “_singleton/core/resource” already exists

Mage registry key “_singleton/core/resource” already exists : is a very common problem during magento update and due to this issues many time we are getting the erros in the page “There has been an error processing your request” . In my case i found the issue is due to cache so what i did i cleaned my cache every time through index.php  of magento .

i found two solution of this problem

Solution One :

Try to add this code in index.php line , this code will delete the cache every time .

$app = Mage::app(); 
if ($app != null) {    
$cache = $app->getCache();    
if ($cache != null)
{        
$cache->clean();    
} }

Solution Two

Go to this location  lib/Zend/Cache/Backend and open file.php  and replace the following code

 protected $_options = array(
        'cache_dir' => NULL,
        'file_locking' => true,
        'read_control' => true,
        'read_control_type' => 'crc32',
        'hashed_directory_level' => 0,
        'hashed_directory_umask' => 0700,
        'file_name_prefix' => 'zend_cache',
        'cache_file_umask' => 0600,
        'metadatas_array_max_size' => 100
    );

with this

 protected $_options = array(
        'cache_dir' => tmp,
        'file_locking' => true,
        'read_control' => true,
        'read_control_type' => 'crc32',
        'hashed_directory_level' => 0,
        'hashed_directory_umask' => 0700,
        'file_name_prefix' => 'zend_cache',
        'cache_file_umask' => 0600,
        'metadatas_array_max_size' => 100
    );

and comment the following code in index.php

if (isset($_SERVER['MAGE_IS_DEVELOPER_MODE'])) {
    Mage::setIsDeveloperMode(true);
}