Function ExecSerializePlan

src/backend/executor/execParallel.c:147–221

* Create a serialized representation of the plan to be sent to each worker. */

 * Create a serialized representation of the plan to be sent to each worker.
 */
static char *
ExecSerializePlan(Plan *plan, EState *estate)
{
	PlannedStmt *pstmt;
	ListCell   *lc;

	/* We can't scribble on the original plan, so make a copy. */
	plan = copyObject(plan);

	/*
	 * The worker will start its own copy of the executor, and that copy will
	 * insert a junk filter if the toplevel node has any resjunk entries. We
	 * don't want that to happen, because while resjunk columns shouldn't be
	 * sent back to the user, here the tuples are coming back to another
	 * backend which may very well need them.  So mutate the target list
	 * accordingly.  This is sort of a hack; there might be better ways to do
	 * this...
	 */
	foreach(lc, plan->targetlist)
	{
		TargetEntry *tle = lfirst_node(TargetEntry, lc);

		tle->resjunk = false;
	}

	/*
	 * Create a dummy PlannedStmt.  Most of the fields don't need to be valid
	 * for our purposes, but the worker will need at least a minimal
	 * PlannedStmt to start the executor.
	 */
	pstmt = makeNode(PlannedStmt);
	pstmt->commandType = CMD_SELECT;
	pstmt->queryId = pgstat_get_my_query_id();
	pstmt->hasReturning = false;
	pstmt->hasModifyingCTE = false;
	pstmt->canSetTag = true;
	pstmt->transientPlan = false;
	pstmt->dependsOnRole = false;
	pstmt->parallelModeNeeded = false;
	pstmt->planTree = plan;
	pstmt->rtable = estate->es_range_table;
	pstmt->resultRelations = NIL;
	pstmt->appendRelations = NIL;

	/*
	 * Transfer only parallel-safe subplans, leaving a NULL "hole" in the list
	 * for unsafe ones (so that the list indexes of the safe ones are
	 * preserved).  This positively ensures that the worker won't try to run,
	 * or even do ExecInitNode on, an unsafe subplan.  That's important to
	 * protect, eg, non-parallel-aware FDWs from getting into trouble.
	 */
	pstmt->subplans = NIL;
	foreach(lc, estate->es_plannedstmt->subplans)
	{
		Plan	   *subplan = (Plan *) lfirst(lc);

		if (subplan && !subplan->parallel_safe)
			subplan = NULL;