@Override
  public String toString() {
    return "IoTDBMemoryBlock{"
        + "name="
        + name
        + ", isReleased="
        + isReleased
        + ", memoryBlockType="
        + memoryBlockType
        + ", totalMemorySizeInBytes="
        + totalMemorySizeInBytes
        + ", usedMemoryInBytes="
        + usedMemoryInBytes
        + '}';
  }
Get the free memory in byte of this memory block
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/memory/AtomicLongMemoryBlock.java