@Override
  public boolean needsCompaction(Collection<HStoreFile> storeFiles,
    List<HStoreFile> filesCompacting) {
    int numCandidates = storeFiles.size() - filesCompacting.size();
    return numCandidates >= comConf.getMinFilesToCompact();
  }
A heuristic method to decide whether to schedule a compaction request
@param storeFiles      files in the store.
@param filesCompacting files being scheduled to compact.
@return true to schedule a request.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/compactions/RatioBasedCompactionPolicy.java