72bbe75d5b
This PR fixes a problem with replacing a node with tablets when RF=N. Currently, this will fail because tablet replica allocation for rebuild will not be able to find a viable destination, as the replacing node is not considered to be a candidate. It cannot be a candidate because replace rolls back on failure and we cannot roll back after tablets were migrated. The solution taken here is to not drain tablet replicas from replaced node during topology request but leave it to happen later after the replaced node is in left state and replacing node is in normal state. The replacing node waits for this draining to be complete on boot before the node is considered booted. Fixes https://github.com/scylladb/scylladb/issues/17025 Nodes in the left state will be kept in tablet replica sets for a while after node replace is done, until the new replica is rebuilt. So we need to know about those node's location (dc, rack) for two reasons: 1) algorithms which work with replica sets filter nodes based on their location. For example materialized views code which pairs base replicas with view replicas filters by datacenter first. 2) tablet scheduler needs to identify each node's location in order to make decisions about new replica placement. It's ok to not know the IP, and we don't keep it. Those nodes will not be present in the IP-based replica sets, e.g. those returned by get_natural_endpoints(), only in host_id-based replica sets. storage_proxy request coordination is not affected. Nodes in the left state are still not present in token ring, and not considered to be members of the ring (datacanter endpoints excludes them). In the future we could make the change even more transparent by only loading locator::node* for those nodes and keeping node* in tablet replica sets. Currently left nodes are never removed from topology, so will accumulate in memory. We could garbage-collect them from topology coordinator if a left node is absent in any replica set. That means we need a new state - left_for_real. Closes scylladb/scylladb#17388 * github.com:scylladb/scylladb: test: py: Add test for view replica pairing after replace raft, api: Add RESTful API to query current leader of a raft group test: test_tablets_removenode: Verify replacing when there is no spare node doc: topology-on-raft: Document replace behavior with tablets tablets, raft topology: Rebuild tablets after replacing node is normal tablets: load_balancer: Access node attributes via node struct tablets: load_balancer: Extract ensure_node() mv: Switch to using host_id-based replica set effective_replication_map: Introduce host_id-based get_replicas() raft topology: Keep nodes in the left state to topology tablets: Introduce read_required_hosts()
Scylla developer documentation
This folder contains developer-oriented documentation concerning the ScyllaDB codebase. We also have a wiki, which contains additional developer-oriented documentation. There is currently no clear definition of what goes where, so when looking for something be sure to check both.
Seastar documentation can be found here.
User documentation can be found on docs.scylladb.com
For information on how to build Scylla and how to contribute visit HACKING.md and CONTRIBUTING.md.