Notices: These are trivial, non-critical errors that PHP encounters while executing a script - for example, accessing a variable that has not yet been defined. By default, such errors are not displayed to the user at all - although, as you will see, you can change this default behaviour.
Warnings: These are more serious errors - for example, attempting to include() a file which does not exist. By default, these errors are displayed to the user, but they do not result in script termination.
Fatal errors: These are critical errors - for example, instantiating an object of a non-existent class, or calling a non-existent function. These errors cause the immediate termination of the script, and PHP’s default behaviour is to display them to the user when they take place.
There is a decent page in the php manual on the subject, in short mysql_pconnect() makes a persevering association with the database which implies a SQL join that don't close when the execution of your script closes. mysql_connect()provides just for the database new association while utilizing mysql_pconnect , the capacity would first attempt to locate a (relentless) connection that is as of now open with the same host, username and password. On the off chance that one is found, an identifier for it will be returned as opposed to opening another connection... the connection with the SQL server won't be terminated when the execution of the script ends. Rather, the link will stay open for future use.
The principle distinction amongst sessions and cookies is that sessions are put away on the server, and cookies are put away on the client's PCs in the content record position. Cookies can not hold various variables,But Session can hold numerous variables.We can set expiry for a cookie,The session just stays dynamic the length of the program is open.Users don't have admittance to the information you put away in Session,Since it is put away in the server. Session is mostly utilized for login/logout reason while cookies utilizing for client movement following.