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If you resolve an INS IOR, the repository ID is not set. This causes the orb to check with the remote orb *every* time an _is_a() or _narrow() is called on that object. If the repository ID is set, this wouldn't be necessary. I believe this can be fixed TAO_GIOP_Invocation::location_forward.
I'll take a look at this.
Sorry it took me so long to look at this one. This is not a bug, there is no way to specify the type_hint for URL-style object references. So the client ORB must use _is_a(). This shouldn't be a problem in general because URL-style object references are intended for bootstrapping a few objects only. If the application really wants to avoid the _is_a() call then a possible workaround is to use _unchecked_narrow().