GreenPlum orca优化器在何处产生执行计划并进行分发

CTranslatorDXLToPlStmt::TranslateDXLTblScan
  if (IMDRelation::ErelstorageExternal == md_rel->RetrieveRelStorageType()){
    ForeignScan *foreign_scan...
    ...
  }else{//创建一个SeqScan节点
    SeqScan *seq_scan = MakeNode(SeqScan);
    seq_scan->scanrelid = index;
    plan = &(seq_scan->plan);
    plan_return = (Plan *) seq_scan;
    plan->targetlist = targetlist;
    plan->qual = qual;
  }
  ...

standard_planner    
  top_plan = create_plan(root, best_path, top_slice);
  Gather     *gather = makeNode(Gather);//创建一个Gather节点
  ...
  top_plan = &gather->plan;