@Override
          public Collection<String> filesUnderSnapshot(final FileSystem fs, final Path snapshotDir)
            throws IOException {
            return SnapshotReferenceUtil.getHFileNames(conf, fs, snapshotDir);
          }
File cache for HFiles in the completed and currently running snapshots
hbase-server/src/main/java/org/apache/hadoop/hbase/master/snapshot/SnapshotHFileCleaner.java