public boolean isReservoirEnabled() {
    return reservoirEnabled;
  }
Initialize an {@link ByteBuffAllocator} which only allocate ByteBuffer from on-heap, it's
designed for testing purpose or disabled reservoir case.
@return allocator to allocate on-heap ByteBuffer.
hbase-common/src/main/java/org/apache/hadoop/hbase/io/ByteBuffAllocator.java