postgres/src/backend/optimizer/util/restrictinfo.c

/*-------------------------------------------------------------------------
 *
 * restrictinfo.c
 *	  RestrictInfo node manipulation routines.
 *
 * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/optimizer/util/restrictinfo.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "optimizer/clauses.h"
#include "optimizer/predtest.h"
#include "optimizer/restrictinfo.h"
#include "optimizer/var.h"


static RestrictInfo *make_restrictinfo_internal(Expr *clause,
						   Expr *orclause,
						   bool is_pushed_down,
						   bool outerjoin_delayed,
						   bool pseudoconstant,
						   Relids required_relids,
						   Relids outer_relids,
						   Relids nullable_relids);
static Expr *make_sub_restrictinfos(Expr *clause,
					   bool is_pushed_down,
					   bool outerjoin_delayed,
					   bool pseudoconstant,
					   Relids required_relids,
					   Relids outer_relids,
					   Relids nullable_relids);


/*
 * make_restrictinfo
 *
 * Build a RestrictInfo node containing the given subexpression.
 *
 * The is_pushed_down, outerjoin_delayed, and pseudoconstant flags for the
 * RestrictInfo must be supplied by the caller, as well as the correct values
 * for outer_relids and nullable_relids.
 * required_relids can be NULL, in which case it defaults to the actual clause
 * contents (i.e., clause_relids).
 *
 * We initialize fields that depend only on the given subexpression, leaving
 * others that depend on context (or may never be needed at all) to be filled
 * later.
 */
RestrictInfo *
make_restrictinfo(Expr *clause,
				  bool is_pushed_down,
				  bool outerjoin_delayed,
				  bool pseudoconstant,
				  Relids required_relids,
				  Relids outer_relids,
				  Relids nullable_relids)
{
	/*
	 * If it's an OR clause, build a modified copy with RestrictInfos inserted
	 * above each subclause of the top-level AND/OR structure.
	 */
	if (or_clause((Node *) clause))
		return (RestrictInfo *) make_sub_restrictinfos(clause,
													   is_pushed_down,
													   outerjoin_delayed,
													   pseudoconstant,
													   required_relids,
													   outer_relids,
													   nullable_relids);

	/* Shouldn't be an AND clause, else AND/OR flattening messed up */
	Assert(!and_clause((Node *) clause));

	return make_restrictinfo_internal(clause,
									  NULL,
									  is_pushed_down,
									  outerjoin_delayed,
									  pseudoconstant,
									  required_relids,
									  outer_relids,
									  nullable_relids);
}

/*
 * make_restrictinfo_from_bitmapqual
 *
 * Given the bitmapqual Path structure for a bitmap indexscan, generate
 * RestrictInfo node(s) equivalent to the condition represented by the
 * indexclauses of the Path structure.
 *
 * The result is a List (effectively, implicit-AND representation) of
 * RestrictInfos.
 *
 * The caller must pass is_pushed_down, but we assume outerjoin_delayed
 * and pseudoconstant are false while outer_relids and nullable_relids
 * are NULL (no other kind of qual should ever get into a bitmapqual).
 *
 * If include_predicates is true, we add any partial index predicates to
 * the explicit index quals.  When this is not true, we return a condition
 * that might be weaker than the actual scan represents.
 *
 * To do this through the normal make_restrictinfo() API, callers would have
 * to strip off the RestrictInfo nodes present in the indexclauses lists, and
 * then make_restrictinfo() would have to build new ones.  It's better to have
 * a specialized routine to allow sharing of RestrictInfos.
 *
 * The qual manipulations here are much the same as in create_bitmap_subplan;
 * keep the two routines in sync!
 */
List *
make_restrictinfo_from_bitmapqual(Path *bitmapqual,
								  bool is_pushed_down,
								  bool include_predicates)
{
	List	   *result;
	ListCell   *l;

	if (IsA(bitmapqual, BitmapAndPath))
	{
		BitmapAndPath *apath = (BitmapAndPath *) bitmapqual;

		/*
		 * There may well be redundant quals among the subplans, since a
		 * top-level WHERE qual might have gotten used to form several
		 * different index quals.  We don't try exceedingly hard to eliminate
		 * redundancies, but we do eliminate obvious duplicates by using
		 * list_concat_unique.
		 */
		result = NIL;
		foreach(l, apath->bitmapquals)
		{
			List	   *sublist;

			sublist = make_restrictinfo_from_bitmapqual((Path *) lfirst(l),
														is_pushed_down,
														include_predicates);
			result = list_concat_unique(result, sublist);
		}
	}
	else if (IsA(bitmapqual, BitmapOrPath))
	{
		BitmapOrPath *opath = (BitmapOrPath *) bitmapqual;
		List	   *withris = NIL;
		List	   *withoutris = NIL;

		/*
		 * Here, we only detect qual-free subplans.  A qual-free subplan would
		 * cause us to generate "... OR true ..."  which we may as well reduce
		 * to just "true".  We do not try to eliminate redundant subclauses
		 * because (a) it's not as likely as in the AND case, and (b) we might
		 * well be working with hundreds or even thousands of OR conditions,
		 * perhaps from a long IN list.  The performance of list_append_unique
		 * would be unacceptable.
		 */
		foreach(l, opath->bitmapquals)
		{
			List	   *sublist;

			sublist = make_restrictinfo_from_bitmapqual((Path *) lfirst(l),
														is_pushed_down,
														include_predicates);
			if (sublist == NIL)
			{
				/*
				 * If we find a qual-less subscan, it represents a constant
				 * TRUE, and hence the OR result is also constant TRUE, so we
				 * can stop here.
				 */
				return NIL;
			}

			/*
			 * If the sublist contains multiple RestrictInfos, we create an
			 * AND subclause.  If there's just one, we have to check if it's
			 * an OR clause, and if so flatten it to preserve AND/OR flatness
			 * of our output.
			 *
			 * We construct lists with and without sub-RestrictInfos, so as
			 * not to have to regenerate duplicate RestrictInfos below.
			 */
			if (list_length(sublist) > 1)
			{
				withris = lappend(withris, make_andclause(sublist));
				sublist = get_actual_clauses(sublist);
				withoutris = lappend(withoutris, make_andclause(sublist));
			}
			else
			{
				RestrictInfo *subri = (RestrictInfo *) linitial(sublist);

				Assert(IsA(subri, RestrictInfo));
				if (restriction_is_or_clause(subri))
				{
					BoolExpr   *subor = (BoolExpr *) subri->orclause;

					Assert(or_clause((Node *) subor));
					withris = list_concat(withris,
										  list_copy(subor->args));
					subor = (BoolExpr *) subri->clause;
					Assert(or_clause((Node *) subor));
					withoutris = list_concat(withoutris,
											 list_copy(subor->args));
				}
				else
				{
					withris = lappend(withris, subri);
					withoutris = lappend(withoutris, subri->clause);
				}
			}
		}

		/*
		 * Avoid generating one-element ORs, which could happen due to
		 * redundancy elimination or ScalarArrayOpExpr quals.
		 */
		if (list_length(withris) <= 1)
			result = withris;
		else
		{
			/* Here's the magic part not available to outside callers */
			result =
				list_make1(make_restrictinfo_internal(make_orclause(withoutris),
													  make_orclause(withris),
													  is_pushed_down,
													  false,
													  false,
													  NULL,
													  NULL,
													  NULL));
		}
	}
	else if (IsA(bitmapqual, IndexPath))
	{
		IndexPath  *ipath = (IndexPath *) bitmapqual;

		result = list_copy(ipath->indexclauses);
		if (include_predicates && ipath->indexinfo->indpred != NIL)
		{
			foreach(l, ipath->indexinfo->indpred)
			{
				Expr	   *pred = (Expr *) lfirst(l);

				/*
				 * We know that the index predicate must have been implied by
				 * the query condition as a whole, but it may or may not be
				 * implied by the conditions that got pushed into the
				 * bitmapqual.  Avoid generating redundant conditions.
				 */
				if (!predicate_implied_by(list_make1(pred), result))
					result = lappend(result,
									 make_restrictinfo(pred,
													   is_pushed_down,
													   false,
													   false,
													   NULL,
													   NULL,
													   NULL));
			}
		}
	}
	else
	{
		elog(ERROR, "unrecognized node type: %d", nodeTag(bitmapqual));
		result = NIL;			/* keep compiler quiet */
	}

	return result;
}

/*
 * make_restrictinfos_from_actual_clauses
 *
 * Given a list of implicitly-ANDed restriction clauses, produce a list
 * of RestrictInfo nodes.  This is used to reconstitute the RestrictInfo
 * representation after doing transformations of a list of clauses.
 *
 * We assume that the clauses are relation-level restrictions and therefore
 * we don't have to worry about is_pushed_down, outerjoin_delayed,
 * outer_relids, and nullable_relids (these can be assumed true, false,
 * NULL, and NULL, respectively).
 * We do take care to recognize pseudoconstant clauses properly.
 */
List *
make_restrictinfos_from_actual_clauses(PlannerInfo *root,
									   List *clause_list)
{
	List	   *result = NIL;
	ListCell   *l;

	foreach(l, clause_list)
	{
		Expr	   *clause = (Expr *) lfirst(l);
		bool		pseudoconstant;
		RestrictInfo *rinfo;

		/*
		 * It's pseudoconstant if it contains no Vars and no volatile
		 * functions.  We probably can't see any sublinks here, so
		 * contain_var_clause() would likely be enough, but for safety use
		 * contain_vars_of_level() instead.
		 */
		pseudoconstant =
			!contain_vars_of_level((Node *) clause, 0) &&
			!contain_volatile_functions((Node *) clause);
		if (pseudoconstant)
		{
			/* tell createplan.c to check for gating quals */
			root->hasPseudoConstantQuals = true;
		}

		rinfo = make_restrictinfo(clause,
								  true,
								  false,
								  pseudoconstant,
								  NULL,
								  NULL,
								  NULL);
		result = lappend(result, rinfo);
	}
	return result;
}

/*
 * make_restrictinfo_internal
 *
 * Common code for the main entry points and the recursive cases.
 */
static RestrictInfo *
make_restrictinfo_internal(Expr *clause,
						   Expr *orclause,
						   bool is_pushed_down,
						   bool outerjoin_delayed,
						   bool pseudoconstant,
						   Relids required_relids,
						   Relids outer_relids,
						   Relids nullable_relids)
{
	RestrictInfo *restrictinfo = makeNode(RestrictInfo);

	restrictinfo->clause = clause;
	restrictinfo->orclause = orclause;
	restrictinfo->is_pushed_down = is_pushed_down;
	restrictinfo->outerjoin_delayed = outerjoin_delayed;
	restrictinfo->pseudoconstant = pseudoconstant;
	restrictinfo->can_join = false;		/* may get set below */
	restrictinfo->outer_relids = outer_relids;
	restrictinfo->nullable_relids = nullable_relids;

	/*
	 * If it's a binary opclause, set up left/right relids info. In any case
	 * set up the total clause relids info.
	 */
	if (is_opclause(clause) && list_length(((OpExpr *) clause)->args) == 2)
	{
		restrictinfo->left_relids = pull_varnos(get_leftop(clause));
		restrictinfo->right_relids = pull_varnos(get_rightop(clause));

		restrictinfo->clause_relids = bms_union(restrictinfo->left_relids,
												restrictinfo->right_relids);

		/*
		 * Does it look like a normal join clause, i.e., a binary operator
		 * relating expressions that come from distinct relations? If so we
		 * might be able to use it in a join algorithm.  Note that this is a
		 * purely syntactic test that is made regardless of context.
		 */
		if (!bms_is_empty(restrictinfo->left_relids) &&
			!bms_is_empty(restrictinfo->right_relids) &&
			!bms_overlap(restrictinfo->left_relids,
						 restrictinfo->right_relids))
		{
			restrictinfo->can_join = true;
			/* pseudoconstant should certainly not be true */
			Assert(!restrictinfo->pseudoconstant);
		}
	}
	else
	{
		/* Not a binary opclause, so mark left/right relid sets as empty */
		restrictinfo->left_relids = NULL;
		restrictinfo->right_relids = NULL;
		/* and get the total relid set the hard way */
		restrictinfo->clause_relids = pull_varnos((Node *) clause);
	}

	/* required_relids defaults to clause_relids */
	if (required_relids != NULL)
		restrictinfo->required_relids = required_relids;
	else
		restrictinfo->required_relids = restrictinfo->clause_relids;

	/*
	 * Fill in all the cacheable fields with "not yet set" markers. None of
	 * these will be computed until/unless needed.  Note in particular that we
	 * don't mark a binary opclause as mergejoinable or hashjoinable here;
	 * that happens only if it appears in the right context (top level of a
	 * joinclause list).
	 */
	restrictinfo->parent_ec = NULL;

	restrictinfo->eval_cost.startup = -1;
	restrictinfo->norm_selec = -1;
	restrictinfo->outer_selec = -1;

	restrictinfo->mergeopfamilies = NIL;

	restrictinfo->left_ec = NULL;
	restrictinfo->right_ec = NULL;
	restrictinfo->left_em = NULL;
	restrictinfo->right_em = NULL;
	restrictinfo->scansel_cache = NIL;

	restrictinfo->outer_is_left = false;

	restrictinfo->hashjoinoperator = InvalidOid;

	restrictinfo->left_bucketsize = -1;
	restrictinfo->right_bucketsize = -1;

	return restrictinfo;
}

/*
 * Recursively insert sub-RestrictInfo nodes into a boolean expression.
 *
 * We put RestrictInfos above simple (non-AND/OR) clauses and above
 * sub-OR clauses, but not above sub-AND clauses, because there's no need.
 * This may seem odd but it is closely related to the fact that we use
 * implicit-AND lists at top level of RestrictInfo lists.  Only ORs and
 * simple clauses are valid RestrictInfos.
 *
 * The same is_pushed_down, outerjoin_delayed, and pseudoconstant flag
 * values can be applied to all RestrictInfo nodes in the result.  Likewise
 * for outer_relids and nullable_relids.
 *
 * The given required_relids are attached to our top-level output,
 * but any OR-clause constituents are allowed to default to just the
 * contained rels.
 */
static Expr *
make_sub_restrictinfos(Expr *clause,
					   bool is_pushed_down,
					   bool outerjoin_delayed,
					   bool pseudoconstant,
					   Relids required_relids,
					   Relids outer_relids,
					   Relids nullable_relids)
{
	if (or_clause((Node *) clause))
	{
		List	   *orlist = NIL;
		ListCell   *temp;

		foreach(temp, ((BoolExpr *) clause)->args)
			orlist = lappend(orlist,
							 make_sub_restrictinfos(lfirst(temp),
													is_pushed_down,
													outerjoin_delayed,
													pseudoconstant,
													NULL,
													outer_relids,
													nullable_relids));
		return (Expr *) make_restrictinfo_internal(clause,
												   make_orclause(orlist),
												   is_pushed_down,
												   outerjoin_delayed,
												   pseudoconstant,
												   required_relids,
												   outer_relids,
												   nullable_relids);
	}
	else if (and_clause((Node *) clause))
	{
		List	   *andlist = NIL;
		ListCell   *temp;

		foreach(temp, ((BoolExpr *) clause)->args)
			andlist = lappend(andlist,
							  make_sub_restrictinfos(lfirst(temp),
													 is_pushed_down,
													 outerjoin_delayed,
													 pseudoconstant,
													 required_relids,
													 outer_relids,
													 nullable_relids));
		return make_andclause(andlist);
	}
	else
		return (Expr *) make_restrictinfo_internal(clause,
												   NULL,
												   is_pushed_down,
												   outerjoin_delayed,
												   pseudoconstant,
												   required_relids,
												   outer_relids,
												   nullable_relids);
}

/*
 * restriction_is_or_clause
 *
 * Returns t iff the restrictinfo node contains an 'or' clause.
 */
bool
restriction_is_or_clause(RestrictInfo *restrictinfo)
{
	if (restrictinfo->orclause != NULL)
		return true;
	else
		return false;
}

/*
 * get_actual_clauses
 *
 * Returns a list containing the bare clauses from 'restrictinfo_list'.
 *
 * This is only to be used in cases where none of the RestrictInfos can
 * be pseudoconstant clauses (for instance, it's OK on indexqual lists).
 */
List *
get_actual_clauses(List *restrictinfo_list)
{
	List	   *result = NIL;
	ListCell   *l;

	foreach(l, restrictinfo_list)
	{
		RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);

		Assert(IsA(rinfo, RestrictInfo));

		Assert(!rinfo->pseudoconstant);

		result = lappend(result, rinfo->clause);
	}
	return result;
}

/*
 * get_all_actual_clauses
 *
 * Returns a list containing the bare clauses from 'restrictinfo_list'.
 *
 * This loses the distinction between regular and pseudoconstant clauses,
 * so be careful what you use it for.
 */
List *
get_all_actual_clauses(List *restrictinfo_list)
{
	List	   *result = NIL;
	ListCell   *l;

	foreach(l, restrictinfo_list)
	{
		RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);

		Assert(IsA(rinfo, RestrictInfo));

		result = lappend(result, rinfo->clause);
	}
	return result;
}

/*
 * extract_actual_clauses
 *
 * Extract bare clauses from 'restrictinfo_list', returning either the
 * regular ones or the pseudoconstant ones per 'pseudoconstant'.
 */
List *
extract_actual_clauses(List *restrictinfo_list,
					   bool pseudoconstant)
{
	List	   *result = NIL;
	ListCell   *l;

	foreach(l, restrictinfo_list)
	{
		RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);

		Assert(IsA(rinfo, RestrictInfo));

		if (rinfo->pseudoconstant == pseudoconstant)
			result = lappend(result, rinfo->clause);
	}
	return result;
}

/*
 * extract_actual_join_clauses
 *
 * Extract bare clauses from 'restrictinfo_list', separating those that
 * syntactically match the join level from those that were pushed down.
 * Pseudoconstant clauses are excluded from the results.
 *
 * This is only used at outer joins, since for plain joins we don't care
 * about pushed-down-ness.
 */
void
extract_actual_join_clauses(List *restrictinfo_list,
							List **joinquals,
							List **otherquals)
{
	ListCell   *l;

	*joinquals = NIL;
	*otherquals = NIL;

	foreach(l, restrictinfo_list)
	{
		RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);

		Assert(IsA(rinfo, RestrictInfo));

		if (rinfo->is_pushed_down)
		{
			if (!rinfo->pseudoconstant)
				*otherquals = lappend(*otherquals, rinfo->clause);
		}
		else
		{
			/* joinquals shouldn't have been marked pseudoconstant */
			Assert(!rinfo->pseudoconstant);
			*joinquals = lappend(*joinquals, rinfo->clause);
		}
	}
}


/*
 * join_clause_is_movable_to
 *		Test whether a join clause is a safe candidate for parameterization
 *		of a scan on the specified base relation.
 *
 * A movable join clause is one that can safely be evaluated at a rel below
 * its normal semantic level (ie, its required_relids), if the values of
 * variables that it would need from other rels are provided.
 *
 * We insist that the clause actually reference the target relation; this
 * prevents undesirable movement of degenerate join clauses, and ensures
 * that there is a unique place that a clause can be moved down to.
 *
 * We cannot move an outer-join clause into the non-nullable side of its
 * outer join, as that would change the results (rows would be suppressed
 * rather than being null-extended).
 *
 * Also there must not be an outer join below the clause that would null the
 * Vars coming from the target relation.  Otherwise the clause might give
 * results different from what it would give at its normal semantic level.
 */
bool
join_clause_is_movable_to(RestrictInfo *rinfo, Index baserelid)
{
	/* Clause must physically reference target rel */
	if (!bms_is_member(baserelid, rinfo->clause_relids))
		return false;

	/* Cannot move an outer-join clause into the join's outer side */
	if (bms_is_member(baserelid, rinfo->outer_relids))
		return false;

	/* Target rel must not be nullable below the clause */
	if (bms_is_member(baserelid, rinfo->nullable_relids))
		return false;

	return true;
}

/*
 * join_clause_is_movable_into
 *		Test whether a join clause is movable and can be evaluated within
 *		the current join context.
 *
 * currentrelids: the relids of the proposed evaluation location
 * current_and_outer: the union of currentrelids and the required_outer
 *		relids (parameterization's outer relations)
 *
 * The API would be a bit clearer if we passed the current relids and the
 * outer relids separately and did bms_union internally; but since most
 * callers need to apply this function to multiple clauses, we make the
 * caller perform the union.
 *
 * Obviously, the clause must only refer to Vars available from the current
 * relation plus the outer rels.  We also check that it does reference at
 * least one current Var, ensuring that the clause will be pushed down to
 * a unique place in a parameterized join tree.  And we check that we're
 * not pushing the clause into its outer-join outer side, nor down into
 * a lower outer join's inner side.
 *
 * The check about pushing a clause down into a lower outer join's inner side
 * is only approximate; it sometimes returns "false" when actually it would
 * be safe to use the clause here because we're still above the outer join
 * in question.  This is okay as long as the answers at different join levels
 * are consistent: it just means we might sometimes fail to push a clause as
 * far down as it could safely be pushed.  It's unclear whether it would be
 * worthwhile to do this more precisely.  (But if it's ever fixed to be
 * exactly accurate, there's an Assert in get_joinrel_parampathinfo() that
 * should be re-enabled.)
 *
 * Note: if this returns true, it means that the clause could be moved to
 * this join relation, but that doesn't mean that this is the lowest join
 * it could be moved to.  Caller may need to make additional calls to verify
 * that this doesn't succeed on either of the inputs of a proposed join.
 *
 * Note: get_joinrel_parampathinfo depends on the fact that if
 * current_and_outer is NULL, this function will always return false
 * (since one or the other of the first two tests must fail).
 */
bool
join_clause_is_movable_into(RestrictInfo *rinfo,
							Relids currentrelids,
							Relids current_and_outer)
{
	/* Clause must be evaluatable given available context */
	if (!bms_is_subset(rinfo->clause_relids, current_and_outer))
		return false;

	/* Clause must physically reference at least one target rel */
	if (!bms_overlap(currentrelids, rinfo->clause_relids))
		return false;

	/* Cannot move an outer-join clause into the join's outer side */
	if (bms_overlap(currentrelids, rinfo->outer_relids))
		return false;

	/*
	 * Target rel(s) must not be nullable below the clause.  This is
	 * approximate, in the safe direction, because the current join might be
	 * above the join where the nulling would happen, in which case the clause
	 * would work correctly here.  But we don't have enough info to be sure.
	 */
	if (bms_overlap(currentrelids, rinfo->nullable_relids))
		return false;

	return true;
}