*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.184 2005/06/13 23:14:48 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.185 2005/06/14 04:04:30 tgl Exp $
*
*-------------------------------------------------------------------------
*/
Relids outer_relids);
static List *find_clauses_for_join(PlannerInfo *root, RelOptInfo *rel,
Relids outer_relids, bool isouterjoin);
+static bool match_variant_ordering(PlannerInfo *root,
+ IndexOptInfo *index,
+ List *restrictclauses,
+ ScanDirection *indexscandir);
+static List *identify_ignorable_ordering_cols(PlannerInfo *root,
+ IndexOptInfo *index,
+ List *restrictclauses);
+static bool match_index_to_query_keys(PlannerInfo *root,
+ IndexOptInfo *index,
+ ScanDirection indexscandir,
+ List *ignorables);
static bool match_boolean_index_clause(Node *clause, int indexcol,
IndexOptInfo *index);
static bool match_special_index_operator(Expr *clause, Oid opclass,
}
/*
- * 4. If the index is ordered, a backwards scan might be
- * interesting. Currently this is only possible for a DESC query
- * result ordering.
+ * 4. If the index is ordered, and there is a requested query
+ * ordering that we failed to match, consider variant ways of
+ * achieving the ordering. Again, this is only interesting
+ * at top level.
*/
- if (istoplevel && index_is_ordered && !isjoininner)
+ if (istoplevel && index_is_ordered && !isjoininner &&
+ root->query_pathkeys != NIL &&
+ pathkeys_useful_for_ordering(root, useful_pathkeys) == 0)
{
- index_pathkeys = build_index_pathkeys(root, index,
- BackwardScanDirection);
- useful_pathkeys = truncate_useless_pathkeys(root, rel,
- index_pathkeys);
- if (useful_pathkeys != NIL)
+ ScanDirection indexscandir;
+
+ if (match_variant_ordering(root, index, restrictclauses,
+ &indexscandir))
{
ipath = create_index_path(root, index,
restrictclauses,
- useful_pathkeys,
- BackwardScanDirection,
+ root->query_pathkeys,
+ indexscandir,
false);
result = lappend(result, ipath);
}
return clause_list;
}
+/****************************************************************************
+ * ---- ROUTINES TO HANDLE PATHKEYS ----
+ ****************************************************************************/
+
+/*
+ * match_variant_ordering
+ * Try to match an index's ordering to the query's requested ordering
+ *
+ * This is used when the index is ordered but a naive comparison fails to
+ * match its ordering (pathkeys) to root->query_pathkeys. It may be that
+ * we need to scan the index backwards. Also, a less naive comparison can
+ * help for both forward and backward indexscans. Columns of the index
+ * that have an equality restriction clause can be ignored in the match;
+ * that is, an index on (x,y) can be considered to match the ordering of
+ * ... WHERE x = 42 ORDER BY y;
+ *
+ * Note: it would be possible to similarly ignore useless ORDER BY items;
+ * that is, an index on just y could be considered to match the ordering of
+ * ... WHERE x = 42 ORDER BY x, y;
+ * But proving that this is safe would require finding a btree opclass
+ * containing both the = operator and the < or > operator in the ORDER BY
+ * item. That's significantly more expensive than what we do here, since
+ * we'd have to look at restriction clauses unrelated to the current index
+ * and search for opclasses without any hint from the index. The practical
+ * use-cases seem to be mostly covered by ignoring index columns, so that's
+ * all we do for now.
+ *
+ * Inputs:
+ * 'index' is the index of interest.
+ * 'restrictclauses' is the list of sublists of restriction clauses
+ * matching the columns of the index (NIL if none)
+ *
+ * Returns TRUE if able to match the requested query pathkeys, FALSE if not.
+ * In the TRUE case, sets '*indexscandir' to either ForwardScanDirection or
+ * BackwardScanDirection to indicate the proper scan direction.
+ */
+static bool
+match_variant_ordering(PlannerInfo *root,
+ IndexOptInfo *index,
+ List *restrictclauses,
+ ScanDirection *indexscandir)
+{
+ List *ignorables;
+
+ /*
+ * Forget the whole thing if not a btree index; our check for ignorable
+ * columns assumes we are dealing with btree opclasses. (It'd be possible
+ * to factor out just the try for backwards indexscan, but considering
+ * that we presently have no orderable indexes except btrees anyway,
+ * it's hardly worth contorting this code for that case.)
+ *
+ * Note: if you remove this, you probably need to put in a check on
+ * amoptionalkey to prevent possible clauseless scan on an index that
+ * won't cope.
+ */
+ if (index->relam != BTREE_AM_OID)
+ return false;
+ /*
+ * Figure out which index columns can be optionally ignored because
+ * they have an equality constraint. This is the same set for either
+ * forward or backward scan, so we do it just once.
+ */
+ ignorables = identify_ignorable_ordering_cols(root, index,
+ restrictclauses);
+ /*
+ * Try to match to forward scan, then backward scan. However, we can
+ * skip the forward-scan case if there are no ignorable columns,
+ * because find_usable_indexes() would have found the match already.
+ */
+ if (ignorables &&
+ match_index_to_query_keys(root, index, ForwardScanDirection,
+ ignorables))
+ {
+ *indexscandir = ForwardScanDirection;
+ return true;
+ }
+ if (match_index_to_query_keys(root, index, BackwardScanDirection,
+ ignorables))
+ {
+ *indexscandir = BackwardScanDirection;
+ return true;
+ }
+ return false;
+}
+
+/*
+ * identify_ignorable_ordering_cols
+ * Determine which index columns can be ignored for ordering purposes
+ *
+ * Returns an integer List of column numbers (1-based) of ignorable
+ * columns. The ignorable columns are those that have equality constraints
+ * against pseudoconstants.
+ */
+static List *
+identify_ignorable_ordering_cols(PlannerInfo *root,
+ IndexOptInfo *index,
+ List *restrictclauses)
+{
+ List *result = NIL;
+ int indexcol = 0; /* note this is 0-based */
+ ListCell *l;
+
+ /* restrictclauses is either NIL or has a sublist per column */
+ foreach(l, restrictclauses)
+ {
+ List *sublist = (List *) lfirst(l);
+ Oid opclass = index->classlist[indexcol];
+ ListCell *l2;
+
+ foreach(l2, sublist)
+ {
+ RestrictInfo *rinfo = (RestrictInfo *) lfirst(l2);
+ OpExpr *clause = (OpExpr *) rinfo->clause;
+ Oid clause_op;
+ int op_strategy;
+ bool varonleft;
+ bool ispc;
+
+ /* We know this clause passed match_clause_to_indexcol */
+
+ /* First check for boolean-index cases. */
+ if (IsBooleanOpclass(opclass))
+ {
+ if (match_boolean_index_clause((Node *) clause, indexcol,
+ index))
+ {
+ /*
+ * The clause means either col = TRUE or col = FALSE;
+ * we do not care which, it's an equality constraint
+ * either way.
+ */
+ result = lappend_int(result, indexcol+1);
+ break;
+ }
+ }
+
+ /* Else clause must be a binary opclause. */
+ Assert(IsA(clause, OpExpr));
+
+ /* Determine left/right sides and check the operator */
+ clause_op = clause->opno;
+ if (match_index_to_operand(linitial(clause->args), indexcol,
+ index))
+ {
+ /* clause_op is correct */
+ varonleft = true;
+ }
+ else
+ {
+ Assert(match_index_to_operand(lsecond(clause->args), indexcol,
+ index));
+ /* Must flip operator to get the opclass member */
+ clause_op = get_commutator(clause_op);
+ varonleft = false;
+ }
+ if (!OidIsValid(clause_op))
+ continue; /* ignore non match, per next comment */
+ op_strategy = get_op_opclass_strategy(clause_op, opclass);
+
+ /*
+ * You might expect to see Assert(op_strategy != 0) here,
+ * but you won't: the clause might contain a special indexable
+ * operator rather than an ordinary opclass member. Currently
+ * none of the special operators are very likely to expand to
+ * an equality operator; we do not bother to check, but just
+ * assume no match.
+ */
+ if (op_strategy != BTEqualStrategyNumber)
+ continue;
+
+ /* Now check that other side is pseudoconstant */
+ if (varonleft)
+ ispc = is_pseudo_constant_clause_relids(lsecond(clause->args),
+ rinfo->right_relids);
+ else
+ ispc = is_pseudo_constant_clause_relids(linitial(clause->args),
+ rinfo->left_relids);
+ if (ispc)
+ {
+ result = lappend_int(result, indexcol+1);
+ break;
+ }
+ }
+ indexcol++;
+ }
+ return result;
+}
+
+/*
+ * match_index_to_query_keys
+ * Check a single scan direction for "intelligent" match to query keys
+ *
+ * 'index' is the index of interest.
+ * 'indexscandir' is the scan direction to consider
+ * 'ignorables' is an integer list of indexes of ignorable index columns
+ *
+ * Returns TRUE on successful match (ie, the query_pathkeys can be considered
+ * to match this index).
+ */
+static bool
+match_index_to_query_keys(PlannerInfo *root,
+ IndexOptInfo *index,
+ ScanDirection indexscandir,
+ List *ignorables)
+{
+ List *index_pathkeys;
+ ListCell *index_cell;
+ int index_col;
+ ListCell *r;
+
+ /* Get the pathkeys that exactly describe the index */
+ index_pathkeys = build_index_pathkeys(root, index, indexscandir);
+
+ /*
+ * Can we match to the query's requested pathkeys? The inner loop
+ * skips over ignorable index columns while trying to match.
+ */
+ index_cell = list_head(index_pathkeys);
+ index_col = 0;
+
+ foreach(r, root->query_pathkeys)
+ {
+ List *rsubkey = (List *) lfirst(r);
+
+ for (;;)
+ {
+ List *isubkey;
+
+ if (index_cell == NULL)
+ return false;
+ isubkey = (List *) lfirst(index_cell);
+ index_cell = lnext(index_cell);
+ index_col++; /* index_col is now 1-based */
+ /*
+ * Since we are dealing with canonicalized pathkeys, pointer
+ * comparison is sufficient to determine a match.
+ */
+ if (rsubkey == isubkey)
+ break; /* matched current query pathkey */
+
+ if (!list_member_int(ignorables, index_col))
+ return false; /* definite failure to match */
+ /* otherwise loop around and try to match to next index col */
+ }
+ }
+
+ return true;
+}
+
/****************************************************************************
* ---- PATH CREATION UTILITIES ----
****************************************************************************/
* of RestrictInfos.
*
* This is used to flatten out the result of group_clauses_by_indexkey()
- * to produce an indexclauses list.
+ * to produce an indexclauses list. The original list structure mustn't
+ * be altered, but it's OK to share copies of the underlying RestrictInfos.
*/
List *
flatten_clausegroups_list(List *clausegroups)
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