@Override
    public synchronized boolean init(final RegionEngineOptions opts) {
        if (this.started) {
            LOG.info("[RegionEngine: {}] already started.", this.region);
            return true;
        }
        this.regionOpts = Requires.requireNonNull(opts, "opts");
        this.fsm = new KVStoreStateMachine(this.region, this.storeEngine);

        // node options
        NodeOptions nodeOpts = opts.getNodeOptions();
        if (nodeOpts == null) {
            nodeOpts = new NodeOptions();
        }
        final long metricsReportPeriod = opts.getMetricsReportPeriod();
        if (metricsReportPeriod > 0) {
            // metricsReportPeriod > 0 means enable metrics
            nodeOpts.setEnableMetrics(true);
        }
        final Configuration initialConf = new Configuration();
        if (!initialConf.parse(opts.getInitialServerList())) {
            LOG.error("Fail to parse initial configuration {}.", opts.getInitialServerList());
            return false;
        }
        nodeOpts.setInitialConf(initialConf);
        nodeOpts.setFsm(this.fsm);
        final String raftDataPath = opts.getRaftDataPath();
        try {
            FileUtils.forceMkdir(new File(raftDataPath));
        } catch (final Throwable t) {
            LOG.error("Fail to make dir for raftDataPath {}.", raftDataPath);
            return false;
        }
        if (Strings.isBlank(nodeOpts.getLogUri())) {
            final Path logUri = Paths.get(raftDataPath, "log");
            nodeOpts.setLogUri(logUri.toString());
        }
        if (Strings.isBlank(nodeOpts.getRaftMetaUri())) {
            final Path meteUri = Paths.get(raftDataPath, "meta");
            nodeOpts.setRaftMetaUri(meteUri.toString());
        }
        if (Strings.isBlank(nodeOpts.getSnapshotUri())) {
            final Path snapshotUri = Paths.get(raftDataPath, "snapshot");
            nodeOpts.setSnapshotUri(snapshotUri.toString());
        }
        LOG.info("[RegionEngine: {}], log uri: {}, raft meta uri: {}, snapshot uri: {}.", this.region,
            nodeOpts.getLogUri(), nodeOpts.getRaftMetaUri(), nodeOpts.getSnapshotUri());
        final Endpoint serverAddress = opts.getServerAddress();
        final PeerId serverId = new PeerId(serverAddress, 0);
        final RpcServer rpcServer = this.storeEngine.getRpcServer();
        this.raftGroupService = new RaftGroupService(opts.getRaftGroupId(), serverId, nodeOpts, rpcServer, true);
        this.node = this.raftGroupService.start(false);
        RouteTable.getInstance().updateConfiguration(this.raftGroupService.getGroupId(), nodeOpts.getInitialConf());
        if (this.node != null) {
            final RawKVStore rawKVStore = this.storeEngine.getRawKVStore();
            final Executor readIndexExecutor = this.storeEngine.getReadIndexExecutor();
            this.raftRawKVStore = new RaftRawKVStore(this.node, rawKVStore, readIndexExecutor);
            this.metricsRawKVStore = new MetricsRawKVStore(this.region.getId(), this.raftRawKVStore);
            // metrics config
            if (this.regionMetricsReporter == null && metricsReportPeriod > 0) {
                final MetricRegistry metricRegistry = this.node.getNodeMetrics().getMetricRegistry();
                if (metricRegistry != null) {
                    final ScheduledExecutorService scheduler = this.storeEngine.getMetricsScheduler();
                    // start raft node metrics reporter
                    this.regionMetricsReporter = Slf4jReporter.forRegistry(metricRegistry) //
                        .prefixedWith("region_" + this.region.getId()) //
                        .withLoggingLevel(Slf4jReporter.LoggingLevel.INFO) //
                        .outputTo(LOG) //
                        .scheduleOn(scheduler) //
                        .shutdownExecutorOnStop(scheduler != null) //
                        .build();
                    this.regionMetricsReporter.start(metricsReportPeriod, TimeUnit.SECONDS);
                }
            }
            this.started = true;
            LOG.info("[RegionEngine] start successfully: {}.", this);
        }
        return this.started;
    }
Minimum execution/copy unit of RheaKVStore.

@author jiachun.fjc
jraft-rheakv/rheakv-core/src/main/java/com/alipay/sofa/jraft/rhea/RegionEngine.java