private CommittedChangeList getChangeListAtOffset(final long offset) throws IOException {
      CommittedChangeList changeList = myPreviousChangeListsCache.get(offset);
      if (changeList == null) {
        changeList = myChangesCacheFile.loadChangeListAt(offset);
        myPreviousChangeListsCache.put(offset, changeList);
      }
      return changeList;
    }
private CommittedChangeList getChangeListAtOffset(final long offset)