NOCOPY Hint

The NOCOPY hint tells the PL/SQL compiler to pass OUT and IN OUT parameters by reference, rather than by value.

When parameters are passed by value, the contents of the OUT and IN OUT parameters are copied to temporary variables, which are then used by the subprogram being called.  On successful completion of the subprogram the values are copied back to the actual parameters, but unhandled exceptions result in the original parameter values being left unchanged.  The process of copying large parameters, such as records, collections, and objects requires both time and memory which affects performance.

With the NOCOPY hint the parameters are passed by reference and on successful completion the outcome is the same, but unhandled exceptions may leave the parameters in an altered state, so programs must handle errors or cope with the suspect values.