public ConcurrentMap<Long, DiskRegionInfo> get() {
      ConcurrentMap<Long, DiskRegionInfo> regionConcurrentMap = regionMap.get();
      return regionConcurrentMap != null ? regionConcurrentMap : new ConcurrentHashMap<>();
    }
Used to track all information's about live entries that region has in this oplog.
That information is only needed until oplog is compacted. This is because compaction will
clear all live entries from this oplog.
geode-core/src/main/java/org/apache/geode/internal/cache/Oplog.java