private void writeTestData(HRegion region) throws IOException {
    for (int i = 0; i < NUM_ROWS; ++i) {
      Put put = new Put(Bytes.toBytes("row" + i));
      for (int j = 0; j < NUM_COLS_PER_ROW; ++j) {
        for (long ts = 1; ts < NUM_TIMESTAMPS_PER_COL; ++ts) {
          put.addColumn(CF_BYTES, Bytes.toBytes("col" + j), ts,
            Bytes.toBytes("value" + i + "_" + j + "_" + ts));
        }
      }
      region.put(put);
      if ((i + 1) % ROWS_PER_HFILE == 0) {
        region.flush(true);
      }
    }
  }
Extremely small block size, so that we can get some index blocks
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestForceCacheImportantBlocks.java