@Override
    public Long startCacheFlush(final byte[] encodedRegionName, Set<byte[]> flushedFamilyNames) {
      if (closed.get()) return null;
      return HConstants.NO_SEQNUM;
    }
No-op implementation of {@link WALProvider} used when the WAL is disabled. Should only be used
when severe data loss is acceptable.
hbase-server/src/main/java/org/apache/hadoop/hbase/wal/DisabledWALProvider.java