And for resource limitations (resources = bandwidth,cpu,memory.. whatever), the client would simply refuse to perform the search if it gets too heavy (decided on factors that the client are to decide, not part of the actual protocol). And I belive that everyone agrees that a client refusing to perform the search due to resource limits is a fully acceptable reason.

This is something we want to avoid I believe...if the system as a whole
starts skipping too many searches, users will learn that they get different
results if they search more times, and that's bad...it's more or less like
the old multitasking systems that gave priority to processes where keyboard
input was being done to improve their responsiveness...it worked until the
users found out that their calculations went faster if they kept pressing a
button while doing it...

/J