IOS-XR does not have a pre-policy prefix limit.
When the limit is reached, the session will not automatically
re-establish. It needs to be manually cleared first.
It has the extra options:
warning-only - does not drop the session.
discard-extra-paths - additionally, drops prefixes after the limit is reached.
restart <minutes> - automatically re-establish the session after the timeout.
I agree with Job that the use of warning-only can lead to unexpected routing,
because there is no control over which prefixes are dropped.
This is a big hammer that only comes down when the other hammers don't work.