接前面，继续进行分析：

前面已经说过，在planner函数运行时，发生了实际物理磁盘访问。

/***************************************************************************** * *       Query optimizer entry point * * To support loadable plugins that monitor or modify planner behavior, * we provide a hook variable that lets a plugin get control before and * after the standard planning process.  The plugin would normally call * standard_planner(). * * Note to plugin authors: standard_planner() scribbles on its Query input, * so you'd better copy that data structure if you want to plan more than once. * *****************************************************************************/PlannedStmt *planner(Query *parse, int cursorOptions, ParamListInfo boundParams){    PlannedStmt *result;    if (planner_hook)        result = (*planner_hook) (parse, cursorOptions, boundParams);    else        result = standard_planner(parse, cursorOptions, boundParams);    return result;}PlannedStmt *standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams){    .../* primary planning entry point (may recurse for subqueries) */    top_plan = subquery_planner(glob, parse, NULL,                                false, tuple_fraction, &root);    ...    top_plan = set_plan_references(root, top_plan);    ...    forboth(lp, glob->subplans, lr, glob->subroots)    {        Plan       *subplan = (Plan *) lfirst(lp);        PlannerInfo *subroot = (PlannerInfo *) lfirst(lr);        lfirst(lp) = set_plan_references(subroot, subplan);    }/* build the PlannedStmt result */    result = makeNode(PlannedStmt);    ...    return result;}

接着，要分析 subquery_planner