code: public int getCacheIdsSize(boolean filter) {
          if (filter == CacheOnDisk.FILTER) {
              return htod.getCacheIdsSize(filter) - htod.invalidationBuffer.size();
          } else {
              return htod.getCacheIdsSize(filter);
          }
  
      }
docs: Call this method to get the number of the cache ids in the disk.
  
  @param filter
  if true, filter the size from the invalidation buffer. Else, no filter - real size of entries in the
  disk
  @return int - the size