Generate view updates from a pending base replica if it's a reading
replica, i.e. it's in the last stage of transition write_both_read_new
before becoming the new base replica.
Previously we didn't generate view updates on a pending replica. The
problem with that is that when a base token is migrated from one replica
B1 to another B2, at one stage we generate view updates only from B1,
then at the next stage we generate view updates only from B2. During
this transition, it can happen that for some write neither B1 nor B2
generate view update, because each one sees the other as the base
replica.
We fix this by generating view updates from both base replicas in the
phase before the transition. We can generate view updates on the pending
replica in this case, even if it requires read-before-write, because
it's in a stage where it contains all data and serves reads.
Fixes https://github.com/scylladb/scylladb/issues/24292
backport not needed - the issue mostly affects MV with tablets which is still experimental
Closesscylladb/scylladb#25904
* github.com:scylladb/scylladb:
test: mv: test view update during topology operations
mv: generate view updates on both shards in intranode migration
mv: generate view updates on pending replica
72609b5f69