public List<Long> getLeaderRegionIds() {
        final List<Long> regionIds = Lists.newArrayListWithCapacity(this.regionEngineTable.size());
        for (final RegionEngine regionEngine : this.regionEngineTable.values()) {
            if (regionEngine.isLeader()) {
                regionIds.add(regionEngine.getRegion().getId());
            }
        }
        return regionIds;
    }
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