define() is notoriously slow. Since the main benefit of APC is to increase the performance of scripts/applications, this mechanism is provided to streamline the process of mass constant definition.
To remove a set of stored constants (without clearing the entire cache), an empty array may be passed as the constants parameter, effectively clearing the stored value(s).
The key serves as the name of the constant set being stored. This key is used to retrieve the stored constants in apc_load_constants().
An associative array of
constant_name => value
constant_name must follow the normal
constant naming rules.
value must evaluate to a scalar value.
The default behaviour for constants is to be declared case-sensitive;
represent different values. If this parameter evaluates to
constants will be declared as case-insensitive symbols.