Fallout of cookie size exceeding the size allocated in a browser

What happens if the size of cookies exceeds the si开发者_高级运维ze allocated for cookies in a browser?

If the entire cookie cannot be stored, the cookie won't be stored at all (at least, not in a compliant implementation). From RFC 2965, Section 5.3:

The information in a Set-Cookie2 response header MUST be retained in its entirety. If for some reason there is inadequate space to store the cookie, it MUST be discarded, not truncated.