#include "postgres.h"

#include "fmgr.h"
#include "commands/explain.h"
#include "optimizer/plancat.h"
#include "optimizer/planner.h"
#include "utils/guc.h"


PG_MODULE_MAGIC;

void		_PG_init(void);
void		_PG_fini(void);

static double scale_factor = 1.0;

static void my_get_relation_info(PlannerInfo *root, Oid relationObjectId,
								 bool inhparent, RelOptInfo *rel);


/*
 * Get control during planner's get_relation_info() function, which sets up
 * a RelOptInfo struct based on the system catalog contents.  We can modify
 * the struct contents to cause the planner to work with a hypothetical
 * situation rather than what's actually in the catalogs.
 *
 * This simplistic example just scales all relation size estimates by a
 * user-settable factor.
 */
static void
my_get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
					 RelOptInfo *rel)
{
	ListCell   *ilist;

	/* Do nothing for an inheritance parent RelOptInfo */
	if (inhparent)
		return;

	rel->pages = (BlockNumber) ceil(rel->pages * scale_factor);
	rel->tuples = ceil(rel->tuples * scale_factor);

	foreach(ilist, rel->indexlist)
	{
		IndexOptInfo *ind = (IndexOptInfo *) lfirst(ilist);

		ind->pages = (BlockNumber) ceil(ind->pages * scale_factor);
		ind->tuples = ceil(ind->tuples * scale_factor);
	}
}


/*
 * _pg_init()			- library load-time initialization
 *
 * DO NOT make this static nor change its name!
 */
void
_PG_init(void)
{
	/* Get into the hooks we need to be in all the time */
	get_relation_info_hook = my_get_relation_info;
	/* Make scale_factor accessible through GUC */
	DefineCustomRealVariable("scale_factor",
							 "",
							 "",
							 &scale_factor,
							 0.0001,
							 1e9,
							 PGC_USERSET,
							 NULL,
							 NULL);
}


/*
 * _PG_fini()			- library unload-time finalization
 *
 * DO NOT make this static nor change its name!
 */
void
_PG_fini(void)
{
	/* Get out of all the hooks (just to be sure) */
	get_relation_info_hook = NULL;
}