1 /*-------------------------------------------------------------------------
4 * Definitions for planner's internal data structures.
7 * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
8 * Portions Copyright (c) 1994, Regents of the University of California
10 * $Id: relation.h,v 1.81 2003/06/15 22:51:45 tgl Exp $
12 *-------------------------------------------------------------------------
17 #include "access/sdir.h"
18 #include "nodes/bitmapset.h"
19 #include "nodes/parsenodes.h"
24 * Set of relation identifiers (indexes into the rangetable).
27 typedef Bitmapset *Relids;
30 * When looking for a "cheapest path", this enum specifies whether we want
31 * cheapest startup cost or cheapest total cost.
33 typedef enum CostSelector
35 STARTUP_COST, TOTAL_COST
39 * The cost estimate produced by cost_qual_eval() includes both a one-time
40 * (startup) cost, and a per-tuple cost.
42 typedef struct QualCost
44 Cost startup; /* one-time cost */
45 Cost per_tuple; /* per-evaluation cost */
50 * Per-relation information for planning/optimization
52 * For planning purposes, a "base rel" is either a plain relation (a table)
53 * or the output of a sub-SELECT or function that appears in the range table.
54 * In either case it is uniquely identified by an RT index. A "joinrel"
55 * is the joining of two or more base rels. A joinrel is identified by
56 * the set of RT indexes for its component baserels. We create RelOptInfo
57 * nodes for each baserel and joinrel, and store them in the Query's
58 * base_rel_list and join_rel_list respectively.
60 * Note that there is only one joinrel for any given set of component
61 * baserels, no matter what order we assemble them in; so an unordered
62 * set is the right datatype to identify it with.
64 * We also have "other rels", which are like base rels in that they refer to
65 * single RT indexes; but they are not part of the join tree, and are stored
66 * in other_rel_list not base_rel_list.
68 * Currently the only kind of otherrels are those made for child relations
69 * of an inheritance scan (SELECT FROM foo*). The parent table's RTE and
70 * corresponding baserel represent the whole result of the inheritance scan.
71 * The planner creates separate RTEs and associated RelOptInfos for each child
72 * table (including the parent table, in its capacity as a member of the
73 * inheritance set). These RelOptInfos are physically identical to baserels,
74 * but are otherrels because they are not in the main join tree. These added
75 * RTEs and otherrels are used to plan the scans of the individual tables in
76 * the inheritance set; then the parent baserel is given an Append plan
77 * comprising the best plans for the individual child tables.
79 * At one time we also made otherrels to represent join RTEs, for use in
80 * handling join alias Vars. Currently this is not needed because all join
81 * alias Vars are expanded to non-aliased form during preprocess_expression.
83 * Parts of this data structure are specific to various scan and join
84 * mechanisms. It didn't seem worth creating new node types for them.
86 * relids - Set of base-relation identifiers; it is a base relation
87 * if there is just one, a join relation if more than one
88 * rows - estimated number of tuples in the relation after restriction
89 * clauses have been applied (ie, output rows of a plan for it)
90 * width - avg. number of bytes per tuple in the relation after the
91 * appropriate projections have been done (ie, output width)
92 * targetlist - List of TargetEntry nodes for the attributes we need
93 * to output from this relation
94 * pathlist - List of Path nodes, one for each potentially useful
95 * method of generating the relation
96 * cheapest_startup_path - the pathlist member with lowest startup cost
97 * (regardless of its ordering)
98 * cheapest_total_path - the pathlist member with lowest total cost
99 * (regardless of its ordering)
100 * cheapest_unique_path - for caching cheapest path to produce unique
101 * (no duplicates) output from relation
102 * pruneable - flag to let the planner know whether it can prune the
103 * pathlist of this RelOptInfo or not.
105 * If the relation is a base relation it will have these fields set:
107 * relid - RTE index (this is redundant with the relids field, but
108 * is provided for convenience of access)
109 * rtekind - distinguishes plain relation, subquery, or function RTE
110 * varlist - list of Vars for physical columns (only if table)
111 * indexlist - list of IndexOptInfo nodes for relation's indexes
112 * (always NIL if it's not a table)
113 * pages - number of disk pages in relation (zero if not a table)
114 * tuples - number of tuples in relation (not considering restrictions)
115 * subplan - plan for subquery (NULL if it's not a subquery)
117 * Note: for a subquery, tuples and subplan are not set immediately
118 * upon creation of the RelOptInfo object; they are filled in when
119 * set_base_rel_pathlist processes the object.
121 * For otherrels that are inheritance children, these fields are filled
122 * in just as for a baserel.
124 * The presence of the remaining fields depends on the restrictions
125 * and joins that the relation participates in:
127 * baserestrictinfo - List of RestrictInfo nodes, containing info about
128 * each qualification clause in which this relation
129 * participates (only used for base rels)
130 * baserestrictcost - Estimated cost of evaluating the baserestrictinfo
131 * clauses at a single tuple (only used for base rels)
132 * outerjoinset - For a base rel: if the rel appears within the nullable
133 * side of an outer join, the set of all relids
134 * participating in the highest such outer join; else NULL.
136 * joininfo - List of JoinInfo nodes, containing info about each join
137 * clause in which this relation participates
138 * index_outer_relids - only used for base rels; set of outer relids
139 * that participate in indexable joinclauses for this rel
140 * index_inner_paths - only used for base rels; list of InnerIndexscanInfo
141 * nodes showing best indexpaths for various subsets of
142 * index_outer_relids.
144 * Note: Keeping a restrictinfo list in the RelOptInfo is useful only for
145 * base rels, because for a join rel the set of clauses that are treated as
146 * restrict clauses varies depending on which sub-relations we choose to join.
147 * (For example, in a 3-base-rel join, a clause relating rels 1 and 2 must be
148 * treated as a restrictclause if we join {1} and {2 3} to make {1 2 3}; but
149 * if we join {1 2} and {3} then that clause will be a restrictclause in {1 2}
150 * and should not be processed again at the level of {1 2 3}.) Therefore,
151 * the restrictinfo list in the join case appears in individual JoinPaths
152 * (field joinrestrictinfo), not in the parent relation. But it's OK for
153 * the RelOptInfo to store the joininfo lists, because those are the same
154 * for a given rel no matter how we form it.
156 * We store baserestrictcost in the RelOptInfo (for base relations) because
157 * we know we will need it at least once (to price the sequential scan)
158 * and may need it multiple times to price index scans.
160 * outerjoinset is used to ensure correct placement of WHERE clauses that
161 * apply to outer-joined relations; we must not apply such WHERE clauses
162 * until after the outer join is performed.
165 typedef enum RelOptKind
169 RELOPT_OTHER_CHILD_REL
172 typedef struct RelOptInfo
176 RelOptKind reloptkind;
178 /* all relations included in this RelOptInfo */
179 Relids relids; /* set of base relids (rangetable indexes) */
181 /* size estimates generated by planner */
182 double rows; /* estimated number of result tuples */
183 int width; /* estimated avg width of result tuples */
185 /* materialization information */
187 List *pathlist; /* Path structures */
188 struct Path *cheapest_startup_path;
189 struct Path *cheapest_total_path;
190 struct Path *cheapest_unique_path;
193 /* information about a base rel (not set for join rels!) */
195 RTEKind rtekind; /* RELATION, SUBQUERY, or FUNCTION */
200 struct Plan *subplan; /* if subquery */
202 /* used by various scans and joins: */
203 List *baserestrictinfo; /* RestrictInfo structures (if
205 QualCost baserestrictcost; /* cost of evaluating the above */
206 Relids outerjoinset; /* set of base relids */
207 List *joininfo; /* JoinInfo structures */
209 /* cached info about inner indexscan paths for relation: */
210 Relids index_outer_relids; /* other relids in indexable join
212 List *index_inner_paths; /* InnerIndexscanInfo nodes */
214 * Inner indexscans are not in the main pathlist because they are
215 * not usable except in specific join contexts. We use the
216 * index_inner_paths list just to avoid recomputing the best inner
217 * indexscan repeatedly for similar outer relations. See comments
218 * for InnerIndexscanInfo.
224 * Per-index information for planning/optimization
226 * Prior to Postgres 7.0, RelOptInfo was used to describe both relations
227 * and indexes, but that created confusion without actually doing anything
228 * useful. So now we have a separate IndexOptInfo struct for indexes.
230 * classlist[], indexkeys[], and ordering[] have ncolumns entries.
231 * Zeroes in the indexkeys[] array indicate index columns that are
232 * expressions; there is one element in indexprs for each such column.
234 * Note: for historical reasons, the classlist and ordering arrays have
235 * an extra entry that is always zero. Some code scans until it sees a
236 * zero entry, rather than looking at ncolumns.
238 * The indexprs and indpred expressions have been run through
239 * eval_const_expressions() for ease of matching to WHERE clauses.
242 typedef struct IndexOptInfo
246 Oid indexoid; /* OID of the index relation */
248 /* statistics from pg_class */
249 long pages; /* number of disk pages in index */
250 double tuples; /* number of index tuples in index */
252 /* index descriptor information */
253 int ncolumns; /* number of columns in index */
254 Oid *classlist; /* OIDs of operator classes for columns */
255 int *indexkeys; /* column numbers of index's keys, or 0 */
256 Oid *ordering; /* OIDs of sort operators for each column */
257 Oid relam; /* OID of the access method (in pg_am) */
259 RegProcedure amcostestimate; /* OID of the access method's cost fcn */
261 List *indexprs; /* expressions for non-simple index columns */
262 List *indpred; /* predicate if a partial index, else NIL */
263 bool unique; /* true if a unique index */
265 /* cached info about inner indexscan paths for index */
266 Relids outer_relids; /* other relids in usable join clauses */
267 List *inner_paths; /* List of InnerIndexscanInfo nodes */
274 * The sort ordering of a path is represented by a list of sublists of
275 * PathKeyItem nodes. An empty list implies no known ordering. Otherwise
276 * the first sublist represents the primary sort key, the second the
277 * first secondary sort key, etc. Each sublist contains one or more
278 * PathKeyItem nodes, each of which can be taken as the attribute that
279 * appears at that sort position. (See the top of optimizer/path/pathkeys.c
280 * for more information.)
283 typedef struct PathKeyItem
287 Node *key; /* the item that is ordered */
288 Oid sortop; /* the ordering operator ('<' op) */
291 * key typically points to a Var node, ie a relation attribute, but it
292 * can also point to an arbitrary expression representing the value
293 * indexed by an index expression.
298 * Type "Path" is used as-is for sequential-scan paths. For other
299 * path types it is the first component of a larger struct.
301 * Note: "pathtype" is the NodeTag of the Plan node we could build from this
302 * Path. It is partially redundant with the Path's NodeTag, but allows us
303 * to use the same Path type for multiple Plan types where there is no need
304 * to distinguish the Plan type during path processing.
311 RelOptInfo *parent; /* the relation this path can build */
313 /* estimated execution costs for path (see costsize.c for more info) */
314 Cost startup_cost; /* cost expended before fetching any
316 Cost total_cost; /* total cost (assuming all tuples
319 NodeTag pathtype; /* tag identifying scan/join method */
321 List *pathkeys; /* sort ordering of path's output */
322 /* pathkeys is a List of Lists of PathKeyItem nodes; see above */
326 * IndexPath represents an index scan. Although an indexscan can only read
327 * a single relation, it can scan it more than once, potentially using a
328 * different index during each scan. The result is the union (OR) of all the
329 * tuples matched during any scan. (The executor is smart enough not to return
330 * the same tuple more than once, even if it is matched in multiple scans.)
332 * 'indexinfo' is a list of IndexOptInfo nodes, one per scan to be performed.
334 * 'indexqual' is a list of index qualifications, also one per scan.
335 * Each entry in 'indexqual' is a sublist of qualification expressions with
336 * implicit AND semantics across the sublist items. Only expressions that
337 * are usable as indexquals (as determined by indxpath.c) may appear here.
338 * NOTE that the semantics of the top-level list in 'indexqual' is OR
339 * combination, while the sublists are implicitly AND combinations!
340 * Also note that indexquals lists do not contain RestrictInfo nodes,
341 * just bare clause expressions.
343 * 'indexjoinclauses' is NIL for an ordinary indexpath (one that does not
344 * use any join clauses in the index conditions). For an innerjoin indexpath,
345 * it has the same structure as 'indexqual', but references the RestrictInfo
346 * nodes from which the indexqual was built, rather than the bare clause
347 * expressions. (Note: there isn't necessarily a one-to-one correspondence
348 * between RestrictInfos and expressions, because of expansion of special
349 * indexable operators.) We need this so that we can eliminate redundant
350 * join clauses when plans are built.
352 * 'indexscandir' is one of:
353 * ForwardScanDirection: forward scan of an ordered index
354 * BackwardScanDirection: backward scan of an ordered index
355 * NoMovementScanDirection: scan of an unordered index, or don't care
356 * (The executor doesn't care whether it gets ForwardScanDirection or
357 * NoMovementScanDirection for an indexscan, but the planner wants to
358 * distinguish ordered from unordered indexes for building pathkeys.)
360 * 'rows' is the estimated result tuple count for the indexscan. This
361 * is the same as path.parent->rows for a simple indexscan, but it is
362 * different for a nestloop inner scan, because the additional indexquals
363 * coming from join clauses make the scan more selective than the parent
364 * rel's restrict clauses alone would do.
367 typedef struct IndexPath
372 List *indexjoinclauses;
373 ScanDirection indexscandir;
374 double rows; /* estimated number of result tuples */
378 * TidPath represents a scan by TID
380 typedef struct TidPath
383 List *tideval; /* qual(s) involving CTID = something */
387 * AppendPath represents an Append plan, ie, successive execution of
388 * several member plans. Currently it is only used to handle expansion
389 * of inheritance trees.
391 typedef struct AppendPath
394 List *subpaths; /* list of component Paths */
398 * ResultPath represents use of a Result plan node, either to compute a
399 * variable-free targetlist or to gate execution of a subplan with a
400 * one-time (variable-free) qual condition. Note that in the former case
401 * path.parent will be NULL; in the latter case it is copied from the subpath.
403 typedef struct ResultPath
411 * MaterialPath represents use of a Material plan node, i.e., caching of
412 * the output of its subpath. This is used when the subpath is expensive
413 * and needs to be scanned repeatedly, or when we need mark/restore ability
414 * and the subpath doesn't have it.
416 typedef struct MaterialPath
423 * UniquePath represents elimination of distinct rows from the output of
426 * This is unlike the other Path nodes in that it can actually generate
427 * two different plans: either hash-based or sort-based implementation.
428 * The decision is sufficiently localized that it's not worth having two
429 * separate Path node types.
431 typedef struct UniquePath
436 double rows; /* estimated number of result tuples */
440 * All join-type paths share these fields.
443 typedef struct JoinPath
449 Path *outerjoinpath; /* path for the outer side of the join */
450 Path *innerjoinpath; /* path for the inner side of the join */
452 List *joinrestrictinfo; /* RestrictInfos to apply to join */
455 * See the notes for RelOptInfo to understand why joinrestrictinfo is
456 * needed in JoinPath, and can't be merged into the parent RelOptInfo.
461 * A nested-loop path needs no special fields.
464 typedef JoinPath NestPath;
467 * A mergejoin path has these fields.
469 * path_mergeclauses lists the clauses (in the form of RestrictInfos)
470 * that will be used in the merge. (Before 7.0, this was a list of bare
471 * clause expressions, but we can save on list memory and cost_qual_eval
472 * work by leaving it in the form of a RestrictInfo list.)
474 * Note that the mergeclauses are a subset of the parent relation's
475 * restriction-clause list. Any join clauses that are not mergejoinable
476 * appear only in the parent's restrict list, and must be checked by a
477 * qpqual at execution time.
479 * outersortkeys (resp. innersortkeys) is NIL if the outer path
480 * (resp. inner path) is already ordered appropriately for the
481 * mergejoin. If it is not NIL then it is a PathKeys list describing
482 * the ordering that must be created by an explicit sort step.
485 typedef struct MergePath
488 List *path_mergeclauses; /* join clauses to be used for
490 List *outersortkeys; /* keys for explicit sort, if any */
491 List *innersortkeys; /* keys for explicit sort, if any */
495 * A hashjoin path has these fields.
497 * The remarks above for mergeclauses apply for hashclauses as well.
499 * Hashjoin does not care what order its inputs appear in, so we have
500 * no need for sortkeys.
503 typedef struct HashPath
506 List *path_hashclauses; /* join clauses used for hashing */
510 * Restriction clause info.
512 * We create one of these for each AND sub-clause of a restriction condition
513 * (WHERE or JOIN/ON clause). Since the restriction clauses are logically
514 * ANDed, we can use any one of them or any subset of them to filter out
515 * tuples, without having to evaluate the rest. The RestrictInfo node itself
516 * stores data used by the optimizer while choosing the best query plan.
518 * If a restriction clause references a single base relation, it will appear
519 * in the baserestrictinfo list of the RelOptInfo for that base rel.
521 * If a restriction clause references more than one base rel, it will
522 * appear in the JoinInfo lists of every RelOptInfo that describes a strict
523 * subset of the base rels mentioned in the clause. The JoinInfo lists are
524 * used to drive join tree building by selecting plausible join candidates.
525 * The clause cannot actually be applied until we have built a join rel
526 * containing all the base rels it references, however.
528 * When we construct a join rel that includes all the base rels referenced
529 * in a multi-relation restriction clause, we place that clause into the
530 * joinrestrictinfo lists of paths for the join rel, if neither left nor
531 * right sub-path includes all base rels referenced in the clause. The clause
532 * will be applied at that join level, and will not propagate any further up
533 * the join tree. (Note: the "predicate migration" code was once intended to
534 * push restriction clauses up and down the plan tree based on evaluation
535 * costs, but it's dead code and is unlikely to be resurrected in the
536 * foreseeable future.)
538 * Note that in the presence of more than two rels, a multi-rel restriction
539 * might reach different heights in the join tree depending on the join
540 * sequence we use. So, these clauses cannot be associated directly with
541 * the join RelOptInfo, but must be kept track of on a per-join-path basis.
543 * When dealing with outer joins we have to be very careful about pushing qual
544 * clauses up and down the tree. An outer join's own JOIN/ON conditions must
545 * be evaluated exactly at that join node, and any quals appearing in WHERE or
546 * in a JOIN above the outer join cannot be pushed down below the outer join.
547 * Otherwise the outer join will produce wrong results because it will see the
548 * wrong sets of input rows. All quals are stored as RestrictInfo nodes
549 * during planning, but there's a flag to indicate whether a qual has been
550 * pushed down to a lower level than its original syntactic placement in the
551 * join tree would suggest. If an outer join prevents us from pushing a qual
552 * down to its "natural" semantic level (the level associated with just the
553 * base rels used in the qual) then the qual will appear in JoinInfo lists
554 * that reference more than just the base rels it actually uses. By
555 * pretending that the qual references all the rels appearing in the outer
556 * join, we prevent it from being evaluated below the outer join's joinrel.
557 * When we do form the outer join's joinrel, we still need to distinguish
558 * those quals that are actually in that join's JOIN/ON condition from those
559 * that appeared higher in the tree and were pushed down to the join rel
560 * because they used no other rels. That's what the ispusheddown flag is for;
561 * it tells us that a qual came from a point above the join of the specific
562 * set of base rels that it uses (or that the JoinInfo structures claim it
563 * uses). A clause that originally came from WHERE will *always* have its
564 * ispusheddown flag set; a clause that came from an INNER JOIN condition,
565 * but doesn't use all the rels being joined, will also have ispusheddown set
566 * because it will get attached to some lower joinrel.
568 * In general, the referenced clause might be arbitrarily complex. The
569 * kinds of clauses we can handle as indexscan quals, mergejoin clauses,
570 * or hashjoin clauses are fairly limited --- the code for each kind of
571 * path is responsible for identifying the restrict clauses it can use
572 * and ignoring the rest. Clauses not implemented by an indexscan,
573 * mergejoin, or hashjoin will be placed in the plan qual or joinqual field
574 * of the finished Plan node, where they will be enforced by general-purpose
575 * qual-expression-evaluation code. (But we are still entitled to count
576 * their selectivity when estimating the result tuple count, if we
577 * can guess what it is...)
580 typedef struct RestrictInfo
584 Expr *clause; /* the represented clause of WHERE or JOIN */
586 bool ispusheddown; /* TRUE if clause was pushed down in level */
588 /* only used if clause is an OR clause: */
589 List *subclauseindices; /* indexes matching subclauses */
590 /* subclauseindices is a List of Lists of IndexOptInfos */
592 /* cache space for costs (currently only used for join clauses) */
593 QualCost eval_cost; /* eval cost of clause; -1 if not yet set */
594 Selectivity this_selec; /* selectivity; -1 if not yet set */
597 * If the clause looks useful for joining --- that is, it is a binary
598 * opclause with nonoverlapping sets of relids referenced in the left
599 * and right sides --- then these two fields are set to sets of the
600 * referenced relids. Otherwise they are both NULL.
602 Relids left_relids; /* relids in left side of join clause */
603 Relids right_relids; /* relids in right side of join clause */
605 /* valid if clause is mergejoinable, else InvalidOid: */
606 Oid mergejoinoperator; /* copy of clause operator */
607 Oid left_sortop; /* leftside sortop needed for mergejoin */
608 Oid right_sortop; /* rightside sortop needed for mergejoin */
610 /* cache space for mergeclause processing; NIL if not yet set */
611 List *left_pathkey; /* canonical pathkey for left side */
612 List *right_pathkey; /* canonical pathkey for right side */
614 /* cache space for mergeclause processing; -1 if not yet set */
615 Selectivity left_mergescansel; /* fraction of left side to scan */
616 Selectivity right_mergescansel; /* fraction of right side to scan */
618 /* valid if clause is hashjoinable, else InvalidOid: */
619 Oid hashjoinoperator; /* copy of clause operator */
621 /* cache space for hashclause processing; -1 if not yet set */
622 Selectivity left_bucketsize; /* avg bucketsize of left side */
623 Selectivity right_bucketsize; /* avg bucketsize of right side */
629 * We make a list of these for each RelOptInfo, containing info about
630 * all the join clauses this RelOptInfo participates in. (For this
631 * purpose, a "join clause" is a WHERE clause that mentions both vars
632 * belonging to this relation and vars belonging to relations not yet
633 * joined to it.) We group these clauses according to the set of
634 * other base relations (unjoined relations) mentioned in them.
635 * There is one JoinInfo for each distinct set of unjoined_relids,
636 * and its jinfo_restrictinfo lists the clause(s) that use that set
637 * of other relations.
640 typedef struct JoinInfo
643 Relids unjoined_relids; /* some rels not yet part of my RelOptInfo */
644 List *jinfo_restrictinfo; /* relevant RestrictInfos */
648 * Inner indexscan info.
650 * An inner indexscan is one that uses one or more joinclauses as index
651 * conditions (perhaps in addition to plain restriction clauses). So it
652 * can only be used as the inner path of a nestloop join where the outer
653 * relation includes all other relids appearing in those joinclauses.
654 * The set of usable joinclauses, and thus the best inner indexscan,
655 * thus varies depending on which outer relation we consider; so we have
656 * to recompute the best such path for every join. To avoid lots of
657 * redundant computation, we cache the results of such searches. For
658 * each index we compute the set of possible otherrelids (all relids
659 * appearing in joinquals that could become indexquals for this index).
660 * Two outer relations whose relids have the same intersection with this
661 * set will have the same set of available joinclauses and thus the same
662 * best inner indexscan for that index. Similarly, for each base relation,
663 * we form the union of the per-index otherrelids sets. Two outer relations
664 * with the same intersection with that set will have the same best overall
665 * inner indexscan for the base relation. We use lists of InnerIndexscanInfo
666 * nodes to cache the results of these searches at both the index and
669 * The search key also includes a bool showing whether the join being
670 * considered is an outer join. Since we constrain the join order for
671 * outer joins, I believe that this bool can only have one possible value
672 * for any particular base relation; but store it anyway to avoid confusion.
675 typedef struct InnerIndexscanInfo
678 /* The lookup key: */
679 Relids other_relids; /* a set of relevant other relids */
680 bool isouterjoin; /* true if join is outer */
681 /* Best path for this lookup key: */
682 Path *best_innerpath; /* best inner indexscan, or NULL if none */
683 } InnerIndexscanInfo;
688 * When we convert top-level IN quals into join operations, we must restrict
689 * the order of joining and use special join methods at some join points.
690 * We record information about each such IN clause in an InClauseInfo struct.
691 * These structs are kept in the Query node's in_info_list.
694 typedef struct InClauseInfo
697 Relids lefthand; /* base relids in lefthand expressions */
698 Relids righthand; /* base relids coming from the subselect */
699 List *sub_targetlist; /* targetlist of original RHS subquery */
701 * Note: sub_targetlist is just a list of Vars or expressions;
702 * it does not contain TargetEntry nodes.
706 #endif /* RELATION_H */