The `topology_coordinator::cleanup_group0_config_if_needed` function first checks whether the number of group 0 members is larger than the number of non-left entries in the topology table, then attempts to remove nodes in left state from group 0 and prints a warning if no such nodes are found. There are some problems with this check:
- Currently, a node is added to group 0 before it inserts its entry to the topology table. Such a node may cause the check to succeed but no nodes will be removed, which will cause the warning to be printed needlessly.
- Cluster features on raft will reverse the situation and it will be possible for an entry in system.topology to exist without the corresponding node being a part of group 0. This, in turn, may cause the check not to pass when it should and nodes could be removed later than necessary.
This commit gets rid of the optimization and the warning, and the topology coordinator will always compute the set of nodes that should be removed. Additionally, the set of nodes to remove is now computed differently: instead of iterating over left nodes and including only those that are in group 0, we now iterate over group 0 members and include those that are in `left` state. As the number of left nodes can potentially grow unbounded and the number of group 0 members is more likely to be bounded, this should give better performance in long-running clusters.
Closes#14238
* github.com:scylladb/scylladb:
storage_service: fix indentation after previous commit
storage_service: remove optimization in cleanup_group0_config_if_needed
23d5ddbecb