public long getStoreUsedSpace() {
        if (this.dbPath == null || !this.dbPath.exists()) {
            return 0;
        }
        return FileUtils.sizeOf(this.dbPath);
    }
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