@Override
      public void call(RegionObserver observer) throws IOException {
        observer.postCompactSelection(this, store, selected, tracker, request);
      }
Called after the {@link HStoreFile}s to be compacted have been selected from the available
candidates.
@param store    The store where compaction is being requested
@param selected The store files selected to compact
@param tracker  used to track the life cycle of a compaction
@param request  the compaction request
@param user     the user
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RegionCoprocessorHost.java