@Override
    public synchronized DiskEntry getPrev() {
      return prev;
    }
Fake disk entry used to implement the circular linked list of entries an oplog has. Each Oplog
will have one OplogDiskEntry whose prev and next fields point to the actual DiskEntrys
currently stored in its crf. Items are added at "next" so the most recent entry written will be
at next and the oldest item written will be at "prev".
geode-core/src/main/java/org/apache/geode/internal/cache/Oplog.java