Codeigniter and oracle undefined constant: OCI_COMMIT_ON_SUCCESS
OCI_COMMIT_ON_SUCCESS is a constant declared in the Oracle PHP extension. Are you sure you have that installed correctly? Is it enabled in php.ini? Can you confirm that you can connect to the database manually with oci_connect?
If you don't have the extension, then you'll need to install it. There is a list of steps I generally take to debug the installation here.
I'm not sure what the value of OCI_COMMIT_ON_SUCCESS is, but you might be able to fake it with your own define, if it comes to that.