private void registerRegionKVService(final RegionKVService regionKVService) {
        final RegionKVService preService = this.regionKVServiceTable.putIfAbsent(regionKVService.getRegionId(),
            regionKVService);
        if (preService != null) {
            throw new RheaRuntimeException("RegionKVService[region=" + regionKVService.getRegionId()
                                           + "] has already been registered, can not register again!");
        }
    }
Storage engine, there is only one instance in a node,
containing one or more {@link RegionEngine}.

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