Function ExecShareInputScan

src/backend/executor/nodeShareInputScan.c:346–400

------------------------------------------------------------------ * ExecShareInputScan * Retrieve a tuple from the ShareInputScan * ------------------------------------------------------------------ */

 * ------------------------------------------------------------------
 */
static TupleTableSlot *
ExecShareInputScan(PlanState *pstate)
{
	ShareInputScanState *node = castNode(ShareInputScanState, pstate);
	ShareInputScan *sisc = (ShareInputScan *) pstate->plan;
	EState	   *estate;
	ScanDirection dir;
	bool		forward;
	TupleTableSlot *slot;

	/*
	 * get state info from node
	 */
	estate = pstate->state;
	dir = estate->es_direction;
	forward = ScanDirectionIsForward(dir);

	if (sisc->this_slice_id != currentSliceId && estate->es_plannedstmt->numSlices != 1)
		elog(ERROR, "cannot execute alien Share Input Scan");

	/* if first time call, need to initialize the tuplestore state.  */
	if (!node->isready)
		init_tuplestore_state(node);
	
	/*
	 * Return NULL when necessary.
	 * This could help improve performance, especially when tuplestore is huge, because ShareInputScan 
	 * do not need to read tuple from tuplestore when discard_output is true, which means current 
	 * ShareInputScan is one but not the last one of Sequence's subplans.
	 */
	if (sisc->discard_output)
		return NULL;

	slot = node->ss.ps.ps_ResultTupleSlot;

	Assert(!node->local_state->closed);

	tuplestore_select_read_pointer(node->ts_state, node->ts_pos);
	while(1)
	{
		bool		gotOK;

		gotOK = tuplestore_gettupleslot(node->ts_state, forward, false, slot);

		if (!gotOK)
			return NULL;

		SIMPLE_FAULT_INJECTOR("execshare_input_next");

		return slot;
	}

	Assert(!"should not be here");
	return NULL;
}

/*  ------------------------------------------------------------------
 * 	ExecInitShareInputScan