Function ExecInitGather

src/backend/executor/nodeGather.c:57–132

---------------------------------------------------------------- * ExecInitGather * ---------------------------------------------------------------- */

 * ----------------------------------------------------------------
 */
GatherState *
ExecInitGather(Gather *node, EState *estate, int eflags)
{
	GatherState *gatherstate;
	Plan	   *outerNode;
	TupleDesc	tupDesc;

	/* Gather node doesn't have innerPlan node. */
	Assert(innerPlan(node) == NULL);

	/*
	 * create state structure
	 */
	gatherstate = makeNode(GatherState);
	gatherstate->ps.plan = (Plan *) node;
	gatherstate->ps.state = estate;
	gatherstate->ps.ExecProcNode = ExecGather;

	gatherstate->initialized = false;
	gatherstate->need_to_scan_locally =
		!node->single_copy && parallel_leader_participation;
	gatherstate->tuples_needed = -1;

	/*
	 * Miscellaneous initialization
	 *
	 * create expression context for node
	 */
	ExecAssignExprContext(estate, &gatherstate->ps);

	/*
	 * now initialize outer plan
	 */
	outerNode = outerPlan(node);
	outerPlanState(gatherstate) = ExecInitNode(outerNode, estate, eflags);
	tupDesc = ExecGetResultType(outerPlanState(gatherstate));

	/*
	 * Leader may access ExecProcNode result directly (if
	 * need_to_scan_locally), or from workers via tuple queue.  So we can't
	 * trivially rely on the slot type being fixed for expressions evaluated
	 * within this node.
	 */
	gatherstate->ps.outeropsset = true;
	gatherstate->ps.outeropsfixed = false;

	/*
	 * Initialize result type and projection.
	 */
	ExecInitResultTypeTL(&gatherstate->ps);
	ExecConditionalAssignProjectionInfo(&gatherstate->ps, tupDesc, OUTER_VAR);

	/*
	 * Without projections result slot type is not trivially known, see
	 * comment above.
	 */
	if (gatherstate->ps.ps_ProjInfo == NULL)
	{