When migrating tablet size during the end_migration tablet transition stage, we need the pending and leaving replica hosts. The leaving and pending replicas are gathered in objects of type std::optional<tablet_replica> and are not checked if they contain a value before dereferencing which could cause an exception in the topology coordinator.
This patch adds a check for leaving and pending replicas, and only performs the tablet size migration if neither are empty.
This bug was introduced in 10f07fb95a
This change also adds the ability to create a tablet size in load_stats during end_migration stage of a tablet rebuild. We compute the new tablet size from by averaging the tablet sizes of the existing replicas.
This change also adds the virtual table tablet_sizes which contains tablet sizes of all the replicas of all the tablets in the cluster.
A version containing this bug has not yet been released, so a backport is not needed.
Closesscylladb/scylladb#27118
* github.com:scylladb/scylladb:
test: add tests for tablet size migration during end_migration
virtual_table: add tablet_sizes virtual table
load_stats: update tablet sizes after migration or rebuild
d4b77c422f