public long spill() throws IOException {
    if (nextSpillPartition == 0) {
      return 0;
    }
    long memFreed = 0;
    for (HybridHashTableContainer container : loadedContainerList) {
      memFreed += container.spillPartition(nextSpillPartition);
      container.setSpill(true);
    }
    nextSpillPartition--;
    return memFreed;
  }
Spill one in-memory partition from tail for all previously loaded HybridHashTableContainers.
Also mark that partition number as spill-on-creation for future created containers.
@return amount of memory freed; 0 if only one last partition is in memory for each container
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/HybridHashTableConf.java