timescaledb/src/sort_transform.c

/*
 * This file and its contents are licensed under the Apache License 2.0.
 * Please see the included NOTICE for copyright information and
 * LICENSE-APACHE for a copy of the license.
 */
#include <postgres.h>
#include <catalog/pg_type.h>
#include <nodes/makefuncs.h>
#include <nodes/nodeFuncs.h>
#include <nodes/plannodes.h>
#include <parser/parsetree.h>
#include <utils/guc.h>
#include <optimizer/planner.h>
#include <optimizer/paths.h>
#include <utils/lsyscache.h>

#include "func_cache.h"
#include "sort_transform.h"

/* This optimizations allows GROUP BY clauses that transform time in
 * order-preserving ways to use indexes on the time field. It works
 * by transforming sorting clauses from their more complex versions
 * to simplified ones that can use the plain index, if the transform
 * is order preserving.
 *
 * For example, an ordering on date_trunc('minute', time) can be transformed
 * to an ordering on time.
 */

extern void ts_sort_transform_optimization(PlannerInfo *root, RelOptInfo *rel);

static Expr *
transform_timestamp_cast(FuncExpr *func)
{
	/*
	 * transform cast from timestamptz to timestamp
	 *
	 * timestamp(var) => var
	 *
	 * proof: timestamp(time1) >= timestamp(time2) iff time1 > time2
	 *
	 */

	Expr *first;

	if (list_length(func->args) != 1)
		return (Expr *) func;

	first = ts_sort_transform_expr(linitial(func->args));
	if (!IsA(first, Var))
		return (Expr *) func;

	return (Expr *) copyObject(first);
}

static Expr *
transform_timestamptz_cast(FuncExpr *func)
{
	/*
	 * Transform cast from date to timestamptz, or timestamp to timestamptz,
	 * or abstime to timestamptz Handles only single-argument versions of the
	 * cast to avoid explicit timezone specifiers
	 *
	 *
	 * timestamptz(var) => var
	 *
	 * proof: timestamptz(time1) >= timestamptz(time2) iff time1 > time2
	 *
	 */

	Expr *first;

	if (list_length(func->args) != 1)
		return (Expr *) func;

	first = ts_sort_transform_expr(linitial(func->args));
	if (!IsA(first, Var))
		return (Expr *) func;

	return (Expr *) copyObject(first);
}

static inline Expr *
transform_time_op_const_interval(OpExpr *op)
{
	/*
	 * optimize timestamp(tz) +/- const interval
	 *
	 * Sort of ts + 1 minute fulfilled by sort of ts
	 */
	if (list_length(op->args) == 2 && IsA(lsecond(op->args), Const))
	{
		Oid left = exprType((Node *) linitial(op->args));
		Oid right = exprType((Node *) lsecond(op->args));

		if ((left == TIMESTAMPOID && right == INTERVALOID) ||
			(left == TIMESTAMPTZOID && right == INTERVALOID) ||
			(left == DATEOID && right == INTERVALOID))
		{
			char *name = get_opname(op->opno);

			if (strncmp(name, "-", NAMEDATALEN) == 0 || strncmp(name, "+", NAMEDATALEN) == 0)
			{
				Expr *first = ts_sort_transform_expr((Expr *) linitial(op->args));

				if (IsA(first, Var))
					return copyObject(first);
			}
		}
	}
	return (Expr *) op;
}

static inline Expr *
transform_int_op_const(OpExpr *op)
{
	/*
	 * Optimize int op const (or const op int), whenever possible. e.g. sort
	 * of  some_int + const fulfilled by sort of some_int same for the
	 * following operator: + - / *
	 *
	 * Note that / is not commutative and const / var does NOT work (namely it
	 * reverses sort order, which we don't handle yet)
	 */
	if (list_length(op->args) == 2 &&
		(IsA(lsecond(op->args), Const) || IsA(linitial(op->args), Const)))
	{
		Oid left = exprType((Node *) linitial(op->args));
		Oid right = exprType((Node *) lsecond(op->args));

		if ((left == INT8OID && right == INT8OID) || (left == INT4OID && right == INT4OID) ||
			(left == INT2OID && right == INT2OID))
		{
			char *name = get_opname(op->opno);

			if (name[1] == '\0')
			{
				switch (name[0])
				{
					case '-':
					case '+':
					case '*':
						/* commutative cases */
						if (IsA(linitial(op->args), Const))
						{
							Expr *nonconst = ts_sort_transform_expr((Expr *) lsecond(op->args));

							if (IsA(nonconst, Var))
								return copyObject(nonconst);
						}
						else
						{
							Expr *nonconst = ts_sort_transform_expr((Expr *) linitial(op->args));

							if (IsA(nonconst, Var))
								return copyObject(nonconst);
						}
						break;
					case '/':
						/* only if second arg is const */
						if (IsA(lsecond(op->args), Const))
						{
							Expr *nonconst = ts_sort_transform_expr((Expr *) linitial(op->args));

							if (IsA(nonconst, Var))
								return copyObject(nonconst);
						}
						break;
				}
			}
		}
	}
	return (Expr *) op;
}

/* sort_transforms_expr returns a simplified sort expression in a form
 * more common for indexes. Must return same data type & collation too.
 *
 * Sort transforms have the following correctness condition:
 *	Any ordering provided by the returned expression is a valid
 *	ordering under the original expression. The reverse need not
 *	be true to apply the transformation to the last member of pathkeys
 *	but it would need to be true to apply the transformation to
 *	arbitrary members of pathkeys.
 *
 * Namely if orig_expr(X) > orig_expr(Y) then
 *			 new_expr(X) > new_expr(Y).
 *
 * Note that if orig_expr(X) = orig_expr(Y) then
 *			 the ordering under new_expr is unconstrained.
 * */
Expr *
ts_sort_transform_expr(Expr *orig_expr)
{
	if (IsA(orig_expr, FuncExpr))
	{
		FuncExpr *func = (FuncExpr *) orig_expr;
		char *func_name = get_func_name(func->funcid);
		FuncInfo *finfo = ts_func_cache_get_bucketing_func(func->funcid);

		if (NULL != finfo)
		{
			if (NULL == finfo->sort_transform)
				return orig_expr;

			return finfo->sort_transform(func);
		}

		if (strncmp(func_name, "timestamp", NAMEDATALEN) == 0)
			return transform_timestamp_cast(func);
		if (strncmp(func_name, "timestamptz", NAMEDATALEN) == 0)
			return transform_timestamptz_cast(func);
	}
	if (IsA(orig_expr, OpExpr))
	{
		OpExpr *op = (OpExpr *) orig_expr;
		Oid type_first = exprType((Node *) linitial(op->args));

		if (type_first == TIMESTAMPOID || type_first == TIMESTAMPTZOID || type_first == DATEOID)
		{
			return transform_time_op_const_interval(op);
		}
		if (type_first == INT2OID || type_first == INT4OID || type_first == INT8OID)
		{
			return transform_int_op_const(op);
		}
	}
	return orig_expr;
}

/*	sort_transform_ec creates a new EquivalenceClass with transformed
 *	expressions if any of the members of the original EC can be transformed for the sort.
 */

static EquivalenceClass *
sort_transform_ec(PlannerInfo *root, EquivalenceClass *orig)
{
	ListCell *lc_member;
	EquivalenceClass *newec = NULL;

	/* check all members, adding only transformable members to new ec */
	foreach (lc_member, orig->ec_members)
	{
		EquivalenceMember *ec_mem = (EquivalenceMember *) lfirst(lc_member);
		Expr *transformed_expr = ts_sort_transform_expr(ec_mem->em_expr);

		if (transformed_expr != ec_mem->em_expr)
		{
			EquivalenceMember *em;
			Oid type_oid = exprType((Node *) transformed_expr);
			List *opfamilies = list_copy(orig->ec_opfamilies);

			/*
			 * if the transform already exists for even one member, assume
			 * exists for all
			 */
			EquivalenceClass *exist = get_eclass_for_sort_expr(root,
															   transformed_expr,
															   ec_mem->em_nullable_relids,
															   opfamilies,
															   type_oid,
															   orig->ec_collation,
															   orig->ec_sortref,
															   ec_mem->em_relids,
															   false);

			if (exist != NULL)
			{
				return exist;
			}

			em = makeNode(EquivalenceMember);

			em->em_expr = transformed_expr;
			em->em_relids = bms_copy(ec_mem->em_relids);
			em->em_nullable_relids = bms_copy(ec_mem->em_nullable_relids);
			em->em_is_const = ec_mem->em_is_const;
			em->em_is_child = ec_mem->em_is_child;
			em->em_datatype = type_oid;

			if (newec == NULL)
			{
				/* lazy create the ec. */
				newec = makeNode(EquivalenceClass);
				newec->ec_opfamilies = opfamilies;
				newec->ec_collation = orig->ec_collation;
				newec->ec_members = NIL;
				newec->ec_sources = list_copy(orig->ec_sources);
				newec->ec_derives = list_copy(orig->ec_derives);
				newec->ec_relids = bms_copy(orig->ec_relids);
				newec->ec_has_const = orig->ec_has_const;
				newec->ec_has_volatile = orig->ec_has_volatile;
				newec->ec_below_outer_join = orig->ec_below_outer_join;
				newec->ec_broken = orig->ec_broken;
				newec->ec_sortref = orig->ec_sortref;
				newec->ec_merged = orig->ec_merged;
			}

			newec->ec_members = lappend(newec->ec_members, em);
		}
	}
	/* if any transforms were found return new ec */
	if (newec != NULL)
	{
		root->eq_classes = lappend(root->eq_classes, newec);
		return newec;
	}
	return NULL;
}

/*
 *	This optimization transforms between equivalent sort operations to try
 *	to find useful indexes.
 *
 *	For example: an ORDER BY date_trunc('minute', time) can be implemented by
 *	an ordering of time.
 */
void
ts_sort_transform_optimization(PlannerInfo *root, RelOptInfo *rel)
{
	/*
	 * We attack this problem in three steps:
	 *
	 * 1) Create a pathkey for the transformed (simplified) sort.
	 *
	 * 2) Use the transformed pathkey to find new useful index paths.
	 *
	 * 3) Transform the  pathkey of the new paths back into the original form
	 * to make this transparent to upper levels in the planner.
	 *
	 */
	ListCell *lc;
	List *transformed_query_pathkey = NIL;
	List *orig_query_pathkeys = root->query_pathkeys;
	PathKey *last_pk;
	PathKey *new_pk;
	EquivalenceClass *transformed;

	/*
	 * nothing to do for empty pathkeys
	 */
	if (orig_query_pathkeys == NIL)
		return;

	/*
	 * These sort transformations are only safe for single member ORDER BY
	 * clauses or as last member of the ORDER BY clause.
	 * Using it for other ORDER BY clauses will result in wrong ordering.
	 */
	last_pk = llast(root->query_pathkeys);
	transformed = sort_transform_ec(root, last_pk->pk_eclass);

	if (transformed == NULL)
		return;

	new_pk = make_canonical_pathkey(root,
									transformed,
									last_pk->pk_opfamily,
									last_pk->pk_strategy,
									last_pk->pk_nulls_first);

	/*
	 * create complete transformed pathkeys
	 */
	foreach (lc, root->query_pathkeys)
	{
		if (lfirst(lc) != last_pk)
			transformed_query_pathkey = lappend(transformed_query_pathkey, lfirst(lc));
		else
			transformed_query_pathkey = lappend(transformed_query_pathkey, new_pk);
	}

	/* search for indexes on transformed pathkeys */
	root->query_pathkeys = transformed_query_pathkey;
	create_index_paths(root, rel);
	root->query_pathkeys = orig_query_pathkeys;

	/*
	 * change returned paths to use original pathkeys. have to go through
	 * all paths since create_index_paths might have modified existing
	 * pathkey. Always safe to do transform since ordering of
	 * transformed_query_pathkey implements ordering of
	 * orig_query_pathkeys.
	 */
	foreach (lc, rel->pathlist)
	{
		Path *path = lfirst(lc);

		if (compare_pathkeys(path->pathkeys, transformed_query_pathkey) == PATHKEYS_EQUAL)
		{
			path->pathkeys = orig_query_pathkeys;
		}
	}
}