Function ExecInitGatherMerge

src/backend/executor/nodeGatherMerge.c:71–178

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

 * ----------------------------------------------------------------
 */
GatherMergeState *
ExecInitGatherMerge(GatherMerge *node, EState *estate, int eflags)
{
	GatherMergeState *gm_state;
	Plan	   *outerNode;
	TupleDesc	tupDesc;

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

	/*
	 * create state structure
	 */
	gm_state = makeNode(GatherMergeState);
	gm_state->ps.plan = (Plan *) node;
	gm_state->ps.state = estate;
	gm_state->ps.ExecProcNode = ExecGatherMerge;

	gm_state->initialized = false;
	gm_state->gm_initialized = false;
	gm_state->tuples_needed = -1;

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

	/*
	 * GatherMerge doesn't support checking a qual (it's always more efficient
	 * to do it in the child node).
	 */
	Assert(!node->plan.qual);

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

	/*
	 * 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.
	 */
	gm_state->ps.outeropsset = true;
	gm_state->ps.outeropsfixed = false;

	/*
	 * Store the tuple descriptor into gather merge state, so we can use it
	 * while initializing the gather merge slots.
	 */
	tupDesc = ExecGetResultType(outerPlanState(gm_state));
	gm_state->tupDesc = tupDesc;

	/*