@Override
    public boolean getCacheOnWrite() {
      return cacheConf != null && cacheConf.shouldCacheIndexesOnWrite();
    }
@return true if we are using cache-on-write. This is configured by the caller of the
        constructor by either passing a valid block cache or null.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlockIndex.java