@Override
  public long ramBytesUsed() {
    return INSTANCE_SIZE
        + RamUsageEstimator.sizeOf(threadName)
        + RamUsageEstimator.sizeOf(localPlanNodeId)
        + RamUsageEstimator.sizeOf(fullFragmentInstanceId);
  }
this is set to true after calling isBlocked() at least once which indicates that this
SourceHandle needs to output data.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/exchange/source/SourceHandle.java