Function ExecInitWindowAgg

src/backend/executor/nodeWindowAgg.c:2603–2888

----------------- * ExecInitWindowAgg * * Creates the run-time information for the WindowAgg node produced by the * planner and initializes its outer subtree * ----------------- */

 * -----------------
 */
WindowAggState *
ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
{
	WindowAggState *winstate;
	Plan	   *outerPlan;
	ExprContext *econtext;
	ExprContext *tmpcontext;
	WindowStatePerFunc perfunc;
	WindowStatePerAgg peragg;
	int			frameOptions = node->frameOptions;
	int			numfuncs,
				wfuncno,
				numaggs,
				aggno;
	TupleDesc	scanDesc;
	ListCell   *l;

	/* check for unsupported flags */
	Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));

	/*
	 * create state structure
	 */
	winstate = makeNode(WindowAggState);
	winstate->ss.ps.plan = (Plan *) node;
	winstate->ss.ps.state = estate;
	winstate->ss.ps.ExecProcNode = ExecWindowAgg;

	/*
	 * Create expression contexts.  We need two, one for per-input-tuple
	 * processing and one for per-output-tuple processing.  We cheat a little
	 * by using ExecAssignExprContext() to build both.
	 */
	ExecAssignExprContext(estate, &winstate->ss.ps);
	tmpcontext = winstate->ss.ps.ps_ExprContext;
	winstate->tmpcontext = tmpcontext;
	ExecAssignExprContext(estate, &winstate->ss.ps);

	/* Create long-lived context for storage of partition-local memory etc */
	winstate->partcontext =
		AllocSetContextCreate(CurrentMemoryContext,
							  "WindowAgg Partition",
							  ALLOCSET_DEFAULT_SIZES);

	/*
	 * Create mid-lived context for aggregate trans values etc.
	 *
	 * Note that moving aggregates each use their own private context, not
	 * this one.
	 */
	winstate->aggcontext =
		AllocSetContextCreate(CurrentMemoryContext,
                              "WindowAgg Aggregates",
                              ALLOCSET_DEFAULT_SIZES);

	/*
	 * WindowAgg nodes never have quals, since they can only occur at the
	 * logical top level of a query (ie, after any WHERE or HAVING filters)