public long getBytesToReserve() {
      return bytesToReserve;
    }
MemoryReservationFuture is created when SinkHandle or SourceHandle tries to reserve memory
from pool. This field is max Bytes that SinkHandle or SourceHandle can reserve.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/memory/MemoryPool.java