plancat.c

来自「postgresql8.3.4源码,开源数据库」· C语言 代码 · 共 959 行 · 第 1/2 页

	if (constr != NULL)
	{
		int			num_check = constr->num_check;
		int			i;

		for (i = 0; i < num_check; i++)
		{
			Node	   *cexpr;

			cexpr = stringToNode(constr->check[i].ccbin);

			/*
			 * Run each expression through const-simplification and
			 * canonicalization.  This is not just an optimization, but is
			 * necessary, because we will be comparing it to
			 * similarly-processed qual clauses, and may fail to detect valid
			 * matches without this.  This must match the processing done to
			 * qual clauses in preprocess_expression()!  (We can skip the
			 * stuff involving subqueries, however, since we don't allow any
			 * in check constraints.)
			 */
			cexpr = eval_const_expressions(root, cexpr);

			cexpr = (Node *) canonicalize_qual((Expr *) cexpr);

			/*
			 * Also mark any coercion format fields as "don't care", so that
			 * we can match to both explicit and implicit coercions.
			 */
			set_coercionform_dontcare(cexpr);

			/* Fix Vars to have the desired varno */
			if (varno != 1)
				ChangeVarNodes(cexpr, 1, varno, 0);

			/*
			 * Finally, convert to implicit-AND format (that is, a List) and
			 * append the resulting item(s) to our output list.
			 */
			result = list_concat(result,
								 make_ands_implicit((Expr *) cexpr));
		}

		/* Add NOT NULL constraints in expression form, if requested */
		if (include_notnull && constr->has_not_null)
		{
			int		natts = relation->rd_att->natts;

			for (i = 1; i <= natts; i++)
			{
				Form_pg_attribute att = relation->rd_att->attrs[i - 1];

				if (att->attnotnull && !att->attisdropped)
				{
					NullTest *ntest = makeNode(NullTest);

					ntest->arg = (Expr *) makeVar(varno,
												  i,
												  att->atttypid,
												  att->atttypmod,
												  0);
					ntest->nulltesttype = IS_NOT_NULL;
					result = lappend(result, ntest);
				}
			}
		}
	}

	heap_close(relation, NoLock);

	return result;
}


/*
 * relation_excluded_by_constraints
 *
 * Detect whether the relation need not be scanned because it has either
 * self-inconsistent restrictions, or restrictions inconsistent with the
 * relation's CHECK constraints.
 *
 * Note: this examines only rel->relid and rel->baserestrictinfo; therefore
 * it can be called before filling in other fields of the RelOptInfo.
 */
bool
relation_excluded_by_constraints(PlannerInfo *root,
								 RelOptInfo *rel, RangeTblEntry *rte)
{
	List	   *safe_restrictions;
	List	   *constraint_pred;
	List	   *safe_constraints;
	ListCell   *lc;

	/* Skip the test if constraint exclusion is disabled */
	if (!constraint_exclusion)
		return false;

	/*
	 * Check for self-contradictory restriction clauses.  We dare not make
	 * deductions with non-immutable functions, but any immutable clauses that
	 * are self-contradictory allow us to conclude the scan is unnecessary.
	 *
	 * Note: strip off RestrictInfo because predicate_refuted_by() isn't
	 * expecting to see any in its predicate argument.
	 */
	safe_restrictions = NIL;
	foreach(lc, rel->baserestrictinfo)
	{
		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);

		if (!contain_mutable_functions((Node *) rinfo->clause))
			safe_restrictions = lappend(safe_restrictions, rinfo->clause);
	}

	if (predicate_refuted_by(safe_restrictions, safe_restrictions))
		return true;

	/* Only plain relations have constraints */
	if (rte->rtekind != RTE_RELATION || rte->inh)
		return false;

	/*
	 * OK to fetch the constraint expressions.  Include "col IS NOT NULL"
	 * expressions for attnotnull columns, in case we can refute those.
	 */
	constraint_pred = get_relation_constraints(root, rte->relid, rel, true);

	/*
	 * We do not currently enforce that CHECK constraints contain only
	 * immutable functions, so it's necessary to check here. We daren't draw
	 * conclusions from plan-time evaluation of non-immutable functions. Since
	 * they're ANDed, we can just ignore any mutable constraints in the list,
	 * and reason about the rest.
	 */
	safe_constraints = NIL;
	foreach(lc, constraint_pred)
	{
		Node	   *pred = (Node *) lfirst(lc);

		if (!contain_mutable_functions(pred))
			safe_constraints = lappend(safe_constraints, pred);
	}

	/*
	 * The constraints are effectively ANDed together, so we can just try to
	 * refute the entire collection at once.  This may allow us to make proofs
	 * that would fail if we took them individually.
	 *
	 * Note: we use rel->baserestrictinfo, not safe_restrictions as might seem
	 * an obvious optimization.  Some of the clauses might be OR clauses that
	 * have volatile and nonvolatile subclauses, and it's OK to make
	 * deductions with the nonvolatile parts.
	 */
	if (predicate_refuted_by(safe_constraints, rel->baserestrictinfo))
		return true;

	return false;
}


/*
 * build_physical_tlist
 *
 * Build a targetlist consisting of exactly the relation's user attributes,
 * in order.  The executor can special-case such tlists to avoid a projection
 * step at runtime, so we use such tlists preferentially for scan nodes.
 *
 * Exception: if there are any dropped columns, we punt and return NIL.
 * Ideally we would like to handle the dropped-column case too.  However this
 * creates problems for ExecTypeFromTL, which may be asked to build a tupdesc
 * for a tlist that includes vars of no-longer-existent types.	In theory we
 * could dig out the required info from the pg_attribute entries of the
 * relation, but that data is not readily available to ExecTypeFromTL.
 * For now, we don't apply the physical-tlist optimization when there are
 * dropped cols.
 *
 * We also support building a "physical" tlist for subqueries, functions,
 * and values lists, since the same optimization can occur in SubqueryScan,
 * FunctionScan, and ValuesScan nodes.
 */
List *
build_physical_tlist(PlannerInfo *root, RelOptInfo *rel)
{
	List	   *tlist = NIL;
	Index		varno = rel->relid;
	RangeTblEntry *rte = planner_rt_fetch(varno, root);
	Relation	relation;
	Query	   *subquery;
	Var		   *var;
	ListCell   *l;
	int			attrno,
				numattrs;
	List	   *colvars;

	switch (rte->rtekind)
	{
		case RTE_RELATION:
			/* Assume we already have adequate lock */
			relation = heap_open(rte->relid, NoLock);

			numattrs = RelationGetNumberOfAttributes(relation);
			for (attrno = 1; attrno <= numattrs; attrno++)
			{
				Form_pg_attribute att_tup = relation->rd_att->attrs[attrno - 1];

				if (att_tup->attisdropped)
				{
					/* found a dropped col, so punt */
					tlist = NIL;
					break;
				}

				var = makeVar(varno,
							  attrno,
							  att_tup->atttypid,
							  att_tup->atttypmod,
							  0);

				tlist = lappend(tlist,
								makeTargetEntry((Expr *) var,
												attrno,
												NULL,
												false));
			}

			heap_close(relation, NoLock);
			break;

		case RTE_SUBQUERY:
			subquery = rte->subquery;
			foreach(l, subquery->targetList)
			{
				TargetEntry *tle = (TargetEntry *) lfirst(l);

				/*
				 * A resjunk column of the subquery can be reflected as
				 * resjunk in the physical tlist; we need not punt.
				 */
				var = makeVar(varno,
							  tle->resno,
							  exprType((Node *) tle->expr),
							  exprTypmod((Node *) tle->expr),
							  0);

				tlist = lappend(tlist,
								makeTargetEntry((Expr *) var,
												tle->resno,
												NULL,
												tle->resjunk));
			}
			break;

		case RTE_FUNCTION:
			expandRTE(rte, varno, 0, true /* include dropped */ ,
					  NULL, &colvars);
			foreach(l, colvars)
			{
				var = (Var *) lfirst(l);

				/*
				 * A non-Var in expandRTE's output means a dropped column;
				 * must punt.
				 */
				if (!IsA(var, Var))
				{
					tlist = NIL;
					break;
				}

				tlist = lappend(tlist,
								makeTargetEntry((Expr *) var,
												var->varattno,
												NULL,
												false));
			}
			break;

		case RTE_VALUES:
			expandRTE(rte, varno, 0, false /* dropped not applicable */ ,
					  NULL, &colvars);
			foreach(l, colvars)
			{
				var = (Var *) lfirst(l);

				tlist = lappend(tlist,
								makeTargetEntry((Expr *) var,
												var->varattno,
												NULL,
												false));
			}
			break;

		default:
			/* caller error */
			elog(ERROR, "unsupported RTE kind %d in build_physical_tlist",
				 (int) rte->rtekind);
			break;
	}

	return tlist;
}

/*
 * restriction_selectivity
 *
 * Returns the selectivity of a specified restriction operator clause.
 * This code executes registered procedures stored in the
 * operator relation, by calling the function manager.
 *
 * See clause_selectivity() for the meaning of the additional parameters.
 */
Selectivity
restriction_selectivity(PlannerInfo *root,
						Oid operator,
						List *args,
						int varRelid)
{
	RegProcedure oprrest = get_oprrest(operator);
	float8		result;

	/*
	 * if the oprrest procedure is missing for whatever reason, use a
	 * selectivity of 0.5
	 */
	if (!oprrest)
		return (Selectivity) 0.5;

	result = DatumGetFloat8(OidFunctionCall4(oprrest,
											 PointerGetDatum(root),
											 ObjectIdGetDatum(operator),
											 PointerGetDatum(args),
											 Int32GetDatum(varRelid)));

	if (result < 0.0 || result > 1.0)
		elog(ERROR, "invalid restriction selectivity: %f", result);

	return (Selectivity) result;
}

/*
 * join_selectivity
 *
 * Returns the selectivity of a specified join operator clause.
 * This code executes registered procedures stored in the
 * operator relation, by calling the function manager.
 */
Selectivity
join_selectivity(PlannerInfo *root,
				 Oid operator,
				 List *args,
				 JoinType jointype)
{
	RegProcedure oprjoin = get_oprjoin(operator);
	float8		result;

	/*
	 * if the oprjoin procedure is missing for whatever reason, use a
	 * selectivity of 0.5
	 */
	if (!oprjoin)
		return (Selectivity) 0.5;

	result = DatumGetFloat8(OidFunctionCall4(oprjoin,
											 PointerGetDatum(root),
											 ObjectIdGetDatum(operator),
											 PointerGetDatum(args),
											 Int16GetDatum(jointype)));

	if (result < 0.0 || result > 1.0)
		elog(ERROR, "invalid join selectivity: %f", result);

	return (Selectivity) result;
}

/*
 * find_inheritance_children
 *
 * Returns a list containing the OIDs of all relations which
 * inherit *directly* from the relation with OID 'inhparent'.
 *
 * XXX might be a good idea to create an index on pg_inherits' inhparent
 * field, so that we can use an indexscan instead of sequential scan here.
 * However, in typical databases pg_inherits won't have enough entries to
 * justify an indexscan...
 */
List *
find_inheritance_children(Oid inhparent)
{
	List	   *list = NIL;
	Relation	relation;
	HeapScanDesc scan;
	HeapTuple	inheritsTuple;
	Oid			inhrelid;
	ScanKeyData key[1];

	/*
	 * Can skip the scan if pg_class shows the relation has never had a
	 * subclass.
	 */
	if (!has_subclass(inhparent))
		return NIL;

	ScanKeyInit(&key[0],
				Anum_pg_inherits_inhparent,
				BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(inhparent));
	relation = heap_open(InheritsRelationId, AccessShareLock);
	scan = heap_beginscan(relation, SnapshotNow, 1, key);
	while ((inheritsTuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
	{
		inhrelid = ((Form_pg_inherits) GETSTRUCT(inheritsTuple))->inhrelid;
		list = lappend_oid(list, inhrelid);
	}
	heap_endscan(scan);
	heap_close(relation, AccessShareLock);
	return list;
}

/*
 * has_subclass
 *
 * In the current implementation, has_subclass returns whether a
 * particular class *might* have a subclass. It will not return the
 * correct result if a class had a subclass which was later dropped.
 * This is because relhassubclass in pg_class is not updated when a
 * subclass is dropped, primarily because of concurrency concerns.
 *
 * Currently has_subclass is only used as an efficiency hack to skip
 * unnecessary inheritance searches, so this is OK.
 */
bool
has_subclass(Oid relationId)
{
	HeapTuple	tuple;
	bool		result;

	tuple = SearchSysCache(RELOID,
						   ObjectIdGetDatum(relationId),
						   0, 0, 0);
	if (!HeapTupleIsValid(tuple))
		elog(ERROR, "cache lookup failed for relation %u", relationId);

	result = ((Form_pg_class) GETSTRUCT(tuple))->relhassubclass;
	ReleaseSysCache(tuple);
	return result;
}

/*
 * has_unique_index
 *
 * Detect whether there is a unique index on the specified attribute
 * of the specified relation, thus allowing us to conclude that all
 * the (non-null) values of the attribute are distinct.
 */
bool
has_unique_index(RelOptInfo *rel, AttrNumber attno)
{
	ListCell   *ilist;

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

		/*
		 * Note: ignore partial indexes, since they don't allow us to conclude
		 * that all attr values are distinct.  We don't take any interest in
		 * expressional indexes either. Also, a multicolumn unique index
		 * doesn't allow us to conclude that just the specified attr is
		 * unique.
		 */
		if (index->unique &&
			index->ncolumns == 1 &&
			index->indexkeys[0] == attno &&
			index->indpred == NIL)
			return true;
	}
	return false;
}