service: raft: rename schema_raft_state_machine to group0_state_machine

Generalize the name so it doesn't suggest that group 0 contains only
schema state.

CMakeLists.txt

@@ -578,7 +578,7 @@ set(scylla_sources
     service/raft/raft_group_registry.cc
     service/raft/raft_rpc.cc
     service/raft/raft_sys_table_storage.cc
-    service/raft/schema_raft_state_machine.cc
+    service/raft/group0_state_machine.cc
     service/storage_proxy.cc
     service/storage_service.cc
     sstables/compress.cc

configure.py

@@ -1001,7 +1001,7 @@ scylla_core = (['replica/database.cc',
                 'mutation_writer/feed_writers.cc',
                 'lang/lua.cc',
                 'lang/wasm.cc',
-                'service/raft/schema_raft_state_machine.cc',
+                'service/raft/group0_state_machine.cc',
                 'service/raft/raft_sys_table_storage.cc',
                 'serializer.cc',
                 'release.cc',

service/raft/group0_state_machine.cc

@@ -5,7 +5,7 @@
 /*
  * SPDX-License-Identifier: AGPL-3.0-or-later
  */
-#include "service/raft/schema_raft_state_machine.hh"
+#include "service/raft/group0_state_machine.hh"
 #include <seastar/core/coroutine.hh>
 #include "service/migration_manager.hh"
 #include "message/messaging_service.hh"
@@ -25,7 +25,7 @@ namespace service {
 
 static logging::logger slogger("schema_raft_sm");
 
-future<> schema_raft_state_machine::apply(std::vector<raft::command_cref> command) {
+future<> group0_state_machine::apply(std::vector<raft::command_cref> command) {
     slogger.trace("apply() is called");
     for (auto&& c : command) {
         auto is = ser::as_input_stream(c);
@@ -37,26 +37,26 @@ future<> schema_raft_state_machine::apply(std::vector<raft::command_cref> comman
     }
 }
 
-future<raft::snapshot_id> schema_raft_state_machine::take_snapshot() {
+future<raft::snapshot_id> group0_state_machine::take_snapshot() {
     return make_ready_future<raft::snapshot_id>(raft::snapshot_id::create_random_id());
 }
 
-void schema_raft_state_machine::drop_snapshot(raft::snapshot_id id) {
+void group0_state_machine::drop_snapshot(raft::snapshot_id id) {
     (void) id;
 }
 
-future<> schema_raft_state_machine::load_snapshot(raft::snapshot_id id) {
+future<> group0_state_machine::load_snapshot(raft::snapshot_id id) {
     return make_ready_future<>();
 }
 
-future<> schema_raft_state_machine::transfer_snapshot(gms::inet_address from, raft::snapshot_id snp) {
+future<> group0_state_machine::transfer_snapshot(gms::inet_address from, raft::snapshot_id snp) {
     // Note that this may bring newer state than the schema state machine raft's
     // log, so some raft entries may be double applied, but since the state
     // machine idempotent it is not a problem.
     return _mm.submit_migration_task(from, false);
 }
 
-future<> schema_raft_state_machine::abort() {
+future<> group0_state_machine::abort() {
     return make_ready_future<>();
 }
 

service/raft/group0_state_machine.hh

@@ -16,12 +16,12 @@ class migration_manager;
 
 class migration_manager;
 
-// Raft state machine implementation for managing schema changes.
-// NOTE: schema raft server is always instantiated on shard 0.
-class schema_raft_state_machine : public raft_state_machine {
+// Raft state machine implementation for managing group 0 changes (e.g. schema changes).
+// NOTE: group 0 raft server is always instantiated on shard 0.
+class group0_state_machine : public raft_state_machine {
     migration_manager& _mm;
 public:
-    schema_raft_state_machine(migration_manager& mm) : _mm(mm) {}
+    group0_state_machine(migration_manager& mm) : _mm(mm) {}
     future<> apply(std::vector<raft::command_cref> command) override;
     future<raft::snapshot_id> take_snapshot() override;
     void drop_snapshot(raft::snapshot_id id) override;

service/raft/raft_group0.cc

@@ -9,7 +9,7 @@
 #include "service/raft/raft_rpc.hh"
 #include "service/raft/raft_gossip_failure_detector.hh"
 #include "service/raft/raft_sys_table_storage.hh"
-#include "service/raft/schema_raft_state_machine.hh"
+#include "service/raft/group0_state_machine.hh"
 
 #include "message/messaging_service.hh"
 #include "cql3/query_processor.hh"
@@ -50,7 +50,7 @@ raft_server_for_group raft_group0::create_server_for_group(raft::group_id gid,
         raft::server_address my_addr) {
 
     _raft_gr.address_map().set(my_addr);
-    auto state_machine = std::make_unique<schema_raft_state_machine>(_mm);
+    auto state_machine = std::make_unique<group0_state_machine>(_mm);
     auto rpc = std::make_unique<raft_rpc>(*state_machine, _ms, _raft_gr.address_map(), gid, my_addr.id);
     // Keep a reference to a specific RPC class.
     auto& rpc_ref = *rpc;