indxpath.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

		{
			if (index->indexkeys[i] == 0)
			{
				if (indexpr_item == NULL)
					elog(ERROR, "wrong number of index expressions");
				indexpr_item = lnext(indexpr_item);
			}
		}
		if (indexpr_item == NULL)
			elog(ERROR, "wrong number of index expressions");
		indexkey = (Node *) lfirst(indexpr_item);

		/*
		 * Does it match the operand?  Again, strip any relabeling.
		 */
		if (indexkey && IsA(indexkey, RelabelType))
			indexkey = (Node *) ((RelabelType *) indexkey)->arg;

		if (equal(indexkey, operand))
			return true;
	}

	return false;
}

/****************************************************************************
 *			----  ROUTINES FOR "SPECIAL" INDEXABLE OPERATORS  ----
 ****************************************************************************/

/*----------
 * These routines handle special optimization of operators that can be
 * used with index scans even though they are not known to the executor's
 * indexscan machinery.  The key idea is that these operators allow us
 * to derive approximate indexscan qual clauses, such that any tuples
 * that pass the operator clause itself must also satisfy the simpler
 * indexscan condition(s).	Then we can use the indexscan machinery
 * to avoid scanning as much of the table as we'd otherwise have to,
 * while applying the original operator as a qpqual condition to ensure
 * we deliver only the tuples we want.	(In essence, we're using a regular
 * index as if it were a lossy index.)
 *
 * An example of what we're doing is
 *			textfield LIKE 'abc%'
 * from which we can generate the indexscanable conditions
 *			textfield >= 'abc' AND textfield < 'abd'
 * which allow efficient scanning of an index on textfield.
 * (In reality, character set and collation issues make the transformation
 * from LIKE to indexscan limits rather harder than one might think ...
 * but that's the basic idea.)
 *
 * Another thing that we do with this machinery is to provide special
 * smarts for "boolean" indexes (that is, indexes on boolean columns
 * that support boolean equality).	We can transform a plain reference
 * to the indexkey into "indexkey = true", or "NOT indexkey" into
 * "indexkey = false", so as to make the expression indexable using the
 * regular index operators.  (As of Postgres 8.1, we must do this here
 * because constant simplification does the reverse transformation;
 * without this code there'd be no way to use such an index at all.)
 *
 * Three routines are provided here:
 *
 * match_special_index_operator() is just an auxiliary function for
 * match_clause_to_indexcol(); after the latter fails to recognize a
 * restriction opclause's operator as a member of an index's opclass,
 * it asks match_special_index_operator() whether the clause should be
 * considered an indexqual anyway.
 *
 * match_boolean_index_clause() similarly detects clauses that can be
 * converted into boolean equality operators.
 *
 * expand_indexqual_conditions() converts a list of lists of RestrictInfo
 * nodes (with implicit AND semantics across list elements) into
 * a list of clauses that the executor can actually handle.  For operators
 * that are members of the index's opclass this transformation is a no-op,
 * but clauses recognized by match_special_index_operator() or
 * match_boolean_index_clause() must be converted into one or more "regular"
 * indexqual conditions.
 *----------
 */

/*
 * match_boolean_index_clause
 *	  Recognize restriction clauses that can be matched to a boolean index.
 *
 * This should be called only when IsBooleanOpclass() recognizes the
 * index's operator class.  We check to see if the clause matches the
 * index's key.
 */
static bool
match_boolean_index_clause(Node *clause,
						   int indexcol,
						   IndexOptInfo *index)
{
	/* Direct match? */
	if (match_index_to_operand(clause, indexcol, index))
		return true;
	/* NOT clause? */
	if (not_clause(clause))
	{
		if (match_index_to_operand((Node *) get_notclausearg((Expr *) clause),
								   indexcol, index))
			return true;
	}

	/*
	 * Since we only consider clauses at top level of WHERE, we can convert
	 * indexkey IS TRUE and indexkey IS FALSE to index searches as well. The
	 * different meaning for NULL isn't important.
	 */
	else if (clause && IsA(clause, BooleanTest))
	{
		BooleanTest *btest = (BooleanTest *) clause;

		if (btest->booltesttype == IS_TRUE ||
			btest->booltesttype == IS_FALSE)
			if (match_index_to_operand((Node *) btest->arg,
									   indexcol, index))
				return true;
	}
	return false;
}

/*
 * match_special_index_operator
 *	  Recognize restriction clauses that can be used to generate
 *	  additional indexscanable qualifications.
 *
 * The given clause is already known to be a binary opclause having
 * the form (indexkey OP pseudoconst) or (pseudoconst OP indexkey),
 * but the OP proved not to be one of the index's opclass operators.
 * Return 'true' if we can do something with it anyway.
 */
static bool
match_special_index_operator(Expr *clause, Oid opclass,
							 bool indexkey_on_left)
{
	bool		isIndexable = false;
	Node	   *rightop;
	Oid			expr_op;
	Const	   *patt;
	Const	   *prefix = NULL;
	Const	   *rest = NULL;

	/*
	 * Currently, all known special operators require the indexkey on the
	 * left, but this test could be pushed into the switch statement if some
	 * are added that do not...
	 */
	if (!indexkey_on_left)
		return false;

	/* we know these will succeed */
	rightop = get_rightop(clause);
	expr_op = ((OpExpr *) clause)->opno;

	/* again, required for all current special ops: */
	if (!IsA(rightop, Const) ||
		((Const *) rightop)->constisnull)
		return false;
	patt = (Const *) rightop;

	switch (expr_op)
	{
		case OID_TEXT_LIKE_OP:
		case OID_BPCHAR_LIKE_OP:
		case OID_NAME_LIKE_OP:
			/* the right-hand const is type text for all of these */
			isIndexable = pattern_fixed_prefix(patt, Pattern_Type_Like,
									  &prefix, &rest) != Pattern_Prefix_None;
			break;

		case OID_BYTEA_LIKE_OP:
			isIndexable = pattern_fixed_prefix(patt, Pattern_Type_Like,
									  &prefix, &rest) != Pattern_Prefix_None;
			break;

		case OID_TEXT_ICLIKE_OP:
		case OID_BPCHAR_ICLIKE_OP:
		case OID_NAME_ICLIKE_OP:
			/* the right-hand const is type text for all of these */
			isIndexable = pattern_fixed_prefix(patt, Pattern_Type_Like_IC,
									  &prefix, &rest) != Pattern_Prefix_None;
			break;

		case OID_TEXT_REGEXEQ_OP:
		case OID_BPCHAR_REGEXEQ_OP:
		case OID_NAME_REGEXEQ_OP:
			/* the right-hand const is type text for all of these */
			isIndexable = pattern_fixed_prefix(patt, Pattern_Type_Regex,
									  &prefix, &rest) != Pattern_Prefix_None;
			break;

		case OID_TEXT_ICREGEXEQ_OP:
		case OID_BPCHAR_ICREGEXEQ_OP:
		case OID_NAME_ICREGEXEQ_OP:
			/* the right-hand const is type text for all of these */
			isIndexable = pattern_fixed_prefix(patt, Pattern_Type_Regex_IC,
									  &prefix, &rest) != Pattern_Prefix_None;
			break;

		case OID_INET_SUB_OP:
		case OID_INET_SUBEQ_OP:
		case OID_CIDR_SUB_OP:
		case OID_CIDR_SUBEQ_OP:
			isIndexable = true;
			break;
	}

	if (prefix)
	{
		pfree(DatumGetPointer(prefix->constvalue));
		pfree(prefix);
	}

	/* done if the expression doesn't look indexable */
	if (!isIndexable)
		return false;

	/*
	 * Must also check that index's opclass supports the operators we will
	 * want to apply.  (A hash index, for example, will not support ">=".)
	 * Currently, only btree supports the operators we need.
	 *
	 * We insist on the opclass being the specific one we expect, else we'd do
	 * the wrong thing if someone were to make a reverse-sort opclass with the
	 * same operators.
	 */
	switch (expr_op)
	{
		case OID_TEXT_LIKE_OP:
		case OID_TEXT_ICLIKE_OP:
		case OID_TEXT_REGEXEQ_OP:
		case OID_TEXT_ICREGEXEQ_OP:
			/* text operators will be used for varchar inputs, too */
			isIndexable =
				(opclass == TEXT_PATTERN_BTREE_OPS_OID) ||
				(opclass == TEXT_BTREE_OPS_OID && lc_collate_is_c()) ||
				(opclass == VARCHAR_PATTERN_BTREE_OPS_OID) ||
				(opclass == VARCHAR_BTREE_OPS_OID && lc_collate_is_c());
			break;

		case OID_BPCHAR_LIKE_OP:
		case OID_BPCHAR_ICLIKE_OP:
		case OID_BPCHAR_REGEXEQ_OP:
		case OID_BPCHAR_ICREGEXEQ_OP:
			isIndexable =
				(opclass == BPCHAR_PATTERN_BTREE_OPS_OID) ||
				(opclass == BPCHAR_BTREE_OPS_OID && lc_collate_is_c());
			break;

		case OID_NAME_LIKE_OP:
		case OID_NAME_ICLIKE_OP:
		case OID_NAME_REGEXEQ_OP:
		case OID_NAME_ICREGEXEQ_OP:
			isIndexable =
				(opclass == NAME_PATTERN_BTREE_OPS_OID) ||
				(opclass == NAME_BTREE_OPS_OID && lc_collate_is_c());
			break;

		case OID_BYTEA_LIKE_OP:
			isIndexable = (opclass == BYTEA_BTREE_OPS_OID);
			break;

		case OID_INET_SUB_OP:
		case OID_INET_SUBEQ_OP:
			isIndexable = (opclass == INET_BTREE_OPS_OID);
			break;

		case OID_CIDR_SUB_OP:
		case OID_CIDR_SUBEQ_OP:
			isIndexable = (opclass == CIDR_BTREE_OPS_OID);
			break;
	}

	return isIndexable;
}

/*
 * expand_indexqual_conditions
 *	  Given a list of sublists of RestrictInfo nodes, produce a flat list
 *	  of index qual clauses.  Standard qual clauses (those in the index's
 *	  opclass) are passed through unchanged.  Boolean clauses and "special"
 *	  index operators are expanded into clauses that the indexscan machinery
 *	  will know what to do with.
 *
 * The input list is ordered by index key, and so the output list is too.
 * (The latter is not depended on by any part of the core planner, I believe,
 * but parts of the executor require it, and so do the amcostestimate
 * functions.)
 */
List *
expand_indexqual_conditions(IndexOptInfo *index, List *clausegroups)
{
	List	   *resultquals = NIL;
	ListCell   *clausegroup_item;
	int			indexcol = 0;
	Oid		   *classes = index->classlist;

	if (clausegroups == NIL)
		return NIL;

	clausegroup_item = list_head(clausegroups);
	do
	{
		Oid			curClass = classes[0];
		ListCell   *l;

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

			/* First check for boolean cases */
			if (IsBooleanOpclass(curClass))
			{
				Expr	   *boolqual;

				boolqual = expand_boolean_index_clause((Node *) rinfo->clause,
													   indexcol,
													   index);
				if (boolqual)
				{
					resultquals = lappend(resultquals,
										  make_restrictinfo(boolqual,
															true,
															false,
															NULL));
					continue;
				}
			}

			resultquals = list_concat(resultquals,
									  expand_indexqual_condition(rinfo,
																 curClass));
		}

		clausegroup_item = lnext(clausegroup_item);

		indexcol++;
		classes++;
	} while (clausegroup_item != NULL && !DoneMatchingIndexKeys(classes));

	Assert(clausegroup_item == NULL);	/* else more groups than indexkeys */

	return resultquals;
}

/*
 * expand_boolean_index_clause
 *	  Convert a clause recognized by match_boolean_index_clause into
 *	  a boolean equality operator clause.
 *
 * Returns NULL if the clause isn't a boolean index qual.
 */
static Expr *
expand_boolean_index_clause(Node *clause,
							int indexcol,
							IndexOptInfo *index)
{
	/* Direct match? */
	if (match_index_to_operand(clause, indexcol, index))
	{
		/* convert to indexkey = TRUE */
		return make_opclause(BooleanEqualOperator, BOOLOID, false,
							 (Expr *) clause,
							 (Expr *) makeBoolConst(true, false));
	}
	/* NOT clause? */
	if (not_clause(clause))
	{
		Node	   *arg = (Node *) get_notclausearg((Expr *) clause);

		/* It must have matched the indexkey */
		Assert(match_index_to_operand(arg, indexcol, index));
		/* convert to indexkey = FALSE */
		return make_opclause(BooleanEqualOperator, BOOLOID, false,
							 (Expr *) arg,
							 (Expr *) makeBoolConst(false, false));
	}
	if (clause && IsA(clause, BooleanTest))
	{
		BooleanTest *btest = (BooleanTest *) clause;
		Node	   *arg = (Node *) btest->arg;

		/* It must have matched the indexkey */
		Assert(match_index_to_operand(arg, indexcol, index));
		if (btest->booltesttype == IS_TRUE)
		{
			/* convert to indexkey = TRUE */
			return make_opclause(BooleanEqualOperator, BOOLOID, false,
								 (Expr *) arg,
								 (Expr *) makeBoolConst(true, false));
		}
		if (btest->booltesttype == IS_FALSE)
		{
			/* convert to indexkey = FALSE */
			return make_opclause(BooleanEqualOperator, BOOLOID, false,
								 (Expr *) arg,
								 (Expr *) makeBoolConst(false, false));
		}
		/* Oops */
		Assert(false);
	}

	return NULL;
}

/*
 * expand_indexqual_condition --- expand a single indexqual condition
 *		(other than a boolean-qual case)
 *
 * The input is a single RestrictInfo, the output a list of RestrictInfos
 */
static List *
expand_indexqual_condition(RestrictInfo *rinfo, Oid opclass)
{
	Expr	   *clause = rinfo->clause;

	/* we know these will succeed */
	Node	   *leftop = get_leftop(clause);
	Node	   *righ