public void registerPlanNodeIdToQueryMemoryMap(
      String queryId, String fragmentInstanceId, String planNodeId) {
    synchronized (queryMemoryReservations) {
      queryMemoryReservations
          .computeIfAbsent(queryId, x -> new ConcurrentHashMap<>())
          .computeIfAbsent(fragmentInstanceId, x -> new ConcurrentHashMap<>())
          .putIfAbsent(planNodeId, 0L);
    }
  }
Before executing, we register memory map which is related to queryId, fragmentInstanceId, and
planNodeId to queryMemoryReservationsMap first.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/memory/MemoryPool.java