Today, the replica allocator uses peer recovery retention leases to
select the best-matched copies when allocating replicas of indices with
soft-deletes. We can employ this mechanism for indices without
soft-deletes because the retaining sequence number of a PRRL is the
persisted global checkpoint (plus one) of that copy. If the primary and
replica have the same retaining sequence number, then we should be able
to perform a noop recovery. The reason is that we must be retaining
translog up to the local checkpoint of the safe commit, which is at most
the global checkpoint of either copy). The only limitation is that we
might not cancel ongoing file-based recoveries with PRRLs for noop
recoveries. We can't make the translog retention policy comply with
PRRLs. We also have this problem with soft-deletes if a PRRL is about to
expire.
Relates #45136
Relates #46959
33204c2055