1 /*-------------------------------------------------------------------------
4 * Definitions for internal planner nodes.
7 * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
8 * Portions Copyright (c) 1994, Regents of the University of California
10 * $Id: relation.h,v 1.53 2001/01/24 19:43:26 momjian Exp $
12 *-------------------------------------------------------------------------
17 #include "access/sdir.h"
18 #include "nodes/parsenodes.h"
22 * List of relation identifiers (indexes into the rangetable).
24 * Note: these are lists of integers, not Nodes.
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
40 * Per-relation information for planning/optimization
42 * For planning purposes, a "base rel" is either a plain relation (a
43 * table) or the output of a sub-SELECT that appears in the range table.
44 * In either case it is uniquely identified by an RT index. A "joinrel"
45 * is the joining of two or more base rels. A joinrel is identified by
46 * the set of RT indexes for its component baserels.
48 * Note that there is only one joinrel for any given set of component
49 * baserels, no matter what order we assemble them in; so an unordered
50 * set is the right datatype to identify it with.
52 * Parts of this data structure are specific to various scan and join
53 * mechanisms. It didn't seem worth creating new node types for them.
55 * relids - List of base-relation identifiers; it is a base relation
56 * if there is just one, a join relation if more than one
57 * rows - estimated number of tuples in the relation after restriction
58 * clauses have been applied (ie, output rows of a plan for it)
59 * width - avg. number of bytes per tuple in the relation after the
60 * appropriate projections have been done (ie, output width)
61 * targetlist - List of TargetEntry nodes for the attributes we need
62 * to output from this relation
63 * pathlist - List of Path nodes, one for each potentially useful
64 * method of generating the relation
65 * cheapest_startup_path - the pathlist member with lowest startup cost
66 * (regardless of its ordering)
67 * cheapest_total_path - the pathlist member with lowest total cost
68 * (regardless of its ordering)
69 * pruneable - flag to let the planner know whether it can prune the
70 * pathlist of this RelOptInfo or not.
72 * * If the relation is a base relation it will have these fields set:
74 * issubquery - true if baserel is a subquery RTE rather than a table
75 * indexed - true if the relation has secondary indices (always false
77 * pages - number of disk pages in relation (zero if a subquery)
78 * tuples - number of tuples in relation (not considering restrictions)
79 * subplan - plan for subquery (NULL if it's a plain table)
81 * Note: for a subquery, tuples and subplan are not set immediately
82 * upon creation of the RelOptInfo object; they are filled in when
83 * set_base_rel_pathlist processes the object.
85 * Note: if a base relation is the root of an inheritance tree
86 * (SELECT FROM foo*) it is still considered a base rel. We will
87 * generate a list of candidate Paths for accessing that table itself,
88 * and also generate baserel RelOptInfo nodes for each child table,
89 * with their own candidate Path lists. Then, an AppendPath is built
90 * from the cheapest Path for each of these tables, and set to be the
91 * only available Path for the inheritance baserel.
93 * * The presence of the remaining fields depends on the restrictions
94 * and joins that the relation participates in:
96 * baserestrictinfo - List of RestrictInfo nodes, containing info about
97 * each qualification clause in which this relation
98 * participates (only used for base rels)
99 * baserestrictcost - Estimated cost of evaluating the baserestrictinfo
100 * clauses at a single tuple (only used for base rels)
101 * outerjoinset - If the rel appears within the nullable side of an outer
102 * join, the list of all relids participating in the highest
103 * such outer join; else NIL (only used for base rels)
104 * joininfo - List of JoinInfo nodes, containing info about each join
105 * clause in which this relation participates
106 * innerjoin - List of Path nodes that represent indices that may be used
107 * as inner paths of nestloop joins. This field is non-null
108 * only for base rels, since join rels have no indices.
110 * Note: Keeping a restrictinfo list in the RelOptInfo is useful only for
111 * base rels, because for a join rel the set of clauses that are treated as
112 * restrict clauses varies depending on which sub-relations we choose to join.
113 * (For example, in a 3-base-rel join, a clause relating rels 1 and 2 must be
114 * treated as a restrictclause if we join {1} and {2 3} to make {1 2 3}; but
115 * if we join {1 2} and {3} then that clause will be a restrictclause in {1 2}
116 * and should not be processed again at the level of {1 2 3}.) Therefore,
117 * the restrictinfo list in the join case appears in individual JoinPaths
118 * (field joinrestrictinfo), not in the parent relation. But it's OK for
119 * the RelOptInfo to store the joininfo lists, because those are the same
120 * for a given rel no matter how we form it.
122 * We store baserestrictcost in the RelOptInfo (for base relations) because
123 * we know we will need it at least once (to price the sequential scan)
124 * and may need it multiple times to price index scans.
126 * outerjoinset is used to ensure correct placement of WHERE clauses that
127 * apply to outer-joined relations; we must not apply such WHERE clauses
128 * until after the outer join is performed.
132 typedef struct RelOptInfo
136 /* all relations included in this RelOptInfo */
137 Relids relids; /* integer list of base relids (RT
140 /* size estimates generated by planner */
141 double rows; /* estimated number of result tuples */
142 int width; /* estimated avg width of result tuples */
144 /* materialization information */
146 List *pathlist; /* Path structures */
147 struct Path *cheapest_startup_path;
148 struct Path *cheapest_total_path;
151 /* information about a base rel (not set for join rels!) */
156 struct Plan *subplan;
158 /* used by various scans and joins: */
159 List *baserestrictinfo; /* RestrictInfo structures (if
161 Cost baserestrictcost; /* cost of evaluating the above */
162 Relids outerjoinset; /* integer list of base relids */
163 List *joininfo; /* JoinInfo structures */
164 List *innerjoin; /* potential indexscans for nestloop joins */
167 * innerjoin indexscans are not in the main pathlist because they are
168 * not usable except in specific join contexts; we have to test before
169 * seeing whether they can be used.
175 * Per-index information for planning/optimization
177 * Prior to Postgres 7.0, RelOptInfo was used to describe both relations
178 * and indexes, but that created confusion without actually doing anything
179 * useful. So now we have a separate IndexOptInfo struct for indexes.
181 * indexoid - OID of the index relation itself
182 * pages - number of disk pages in index
183 * tuples - number of index tuples in index
184 * classlist - List of PG_AMOPCLASS OIDs for the index
185 * indexkeys - List of base-relation attribute numbers that are index keys
186 * ordering - List of PG_OPERATOR OIDs which order the indexscan result
187 * relam - the OID of the pg_am of the index
188 * amcostestimate - OID of the relam's cost estimator
189 * indproc - OID of the function if a functional index, else 0
190 * indpred - index predicate if a partial index, else NULL
191 * lossy - true if index is lossy (may return non-matching tuples)
193 * NB. the last element of the arrays classlist, indexkeys and ordering
197 typedef struct IndexOptInfo
201 Oid indexoid; /* OID of the index relation */
203 /* statistics from pg_class */
207 /* index descriptor information */
208 Oid *classlist; /* classes of AM operators */
209 int *indexkeys; /* keys over which we're indexing */
210 Oid *ordering; /* OIDs of sort operators for each key */
211 Oid relam; /* OID of the access method (in pg_am) */
213 RegProcedure amcostestimate;/* OID of the access method's cost fcn */
215 Oid indproc; /* if a functional index */
216 List *indpred; /* if a partial index */
217 bool lossy; /* if a lossy index */
223 * The sort ordering of a path is represented by a list of sublists of
224 * PathKeyItem nodes. An empty list implies no known ordering. Otherwise
225 * the first sublist represents the primary sort key, the second the
226 * first secondary sort key, etc. Each sublist contains one or more
227 * PathKeyItem nodes, each of which can be taken as the attribute that
228 * appears at that sort position. (See the top of optimizer/path/pathkeys.c
229 * for more information.)
232 typedef struct PathKeyItem
236 Node *key; /* the item that is ordered */
237 Oid sortop; /* the ordering operator ('<' op) */
240 * key typically points to a Var node, ie a relation attribute, but it
241 * can also point to a Func clause representing the value indexed by a
242 * functional index. Someday we might allow arbitrary expressions as
243 * path keys, so don't assume more than you must.
248 * Type "Path" is used as-is for sequential-scan paths. For other
249 * path types it is the first component of a larger struct.
256 RelOptInfo *parent; /* the relation this path can build */
258 /* estimated execution costs for path (see costsize.c for more info) */
259 Cost startup_cost; /* cost expended before fetching any
261 Cost total_cost; /* total cost (assuming all tuples
264 NodeTag pathtype; /* tag identifying scan/join method */
265 /* XXX why is pathtype separate from the NodeTag? */
267 List *pathkeys; /* sort ordering of path's output */
268 /* pathkeys is a List of Lists of PathKeyItem nodes; see above */
272 * IndexPath represents an index scan. Although an indexscan can only read
273 * a single relation, it can scan it more than once, potentially using a
274 * different index during each scan. The result is the union (OR) of all the
275 * tuples matched during any scan. (The executor is smart enough not to return
276 * the same tuple more than once, even if it is matched in multiple scans.)
278 * 'indexid' is a list of index relation OIDs, one per scan to be performed.
280 * 'indexqual' is a list of index qualifications, also one per scan.
281 * Each entry in 'indexqual' is a sublist of qualification expressions with
282 * implicit AND semantics across the sublist items. Only expressions that
283 * are usable as indexquals (as determined by indxpath.c) may appear here.
284 * NOTE that the semantics of the top-level list in 'indexqual' is OR
285 * combination, while the sublists are implicitly AND combinations!
286 * Also note that indexquals lists do not contain RestrictInfo nodes,
287 * just bare clause expressions.
289 * 'indexscandir' is one of:
290 * ForwardScanDirection: forward scan of an ordered index
291 * BackwardScanDirection: backward scan of an ordered index
292 * NoMovementScanDirection: scan of an unordered index, or don't care
293 * (The executor doesn't care whether it gets ForwardScanDirection or
294 * NoMovementScanDirection for an indexscan, but the planner wants to
295 * distinguish ordered from unordered indexes for building pathkeys.)
297 * 'joinrelids' is only used in IndexPaths that are constructed for use
298 * as the inner path of a nestloop join. These paths have indexquals
299 * that refer to values of other rels, so those other rels must be
300 * included in the outer joinrel in order to make a usable join.
302 * 'alljoinquals' is also used only for inner paths of nestloop joins.
303 * This flag is TRUE iff all the indexquals came from non-pushed-down
304 * JOIN/ON conditions, which means the path is safe to use for an outer join.
306 * 'rows' is the estimated result tuple count for the indexscan. This
307 * is the same as path.parent->rows for a simple indexscan, but it is
308 * different for a nestloop inner path, because the additional indexquals
309 * coming from join clauses make the scan more selective than the parent
310 * rel's restrict clauses alone would do.
313 typedef struct IndexPath
318 ScanDirection indexscandir;
319 Relids joinrelids; /* other rels mentioned in indexqual */
320 bool alljoinquals; /* all indexquals derived from JOIN conds? */
321 double rows; /* estimated number of result tuples */
325 * TidPath represents a scan by TID
327 typedef struct TidPath
331 Relids unjoined_relids;/* some rels not yet part of my Path */
335 * AppendPath represents an Append plan, ie, successive execution of
336 * several member plans. Currently it is only used to handle expansion
337 * of inheritance trees.
339 typedef struct AppendPath
342 List *subpaths; /* list of component Paths */
346 * All join-type paths share these fields.
349 typedef struct JoinPath
355 Path *outerjoinpath; /* path for the outer side of the join */
356 Path *innerjoinpath; /* path for the inner side of the join */
358 List *joinrestrictinfo; /* RestrictInfos to apply to join */
361 * See the notes for RelOptInfo to understand why joinrestrictinfo is
362 * needed in JoinPath, and can't be merged into the parent RelOptInfo.
367 * A nested-loop path needs no special fields.
370 typedef JoinPath NestPath;
373 * A mergejoin path has these fields.
375 * path_mergeclauses lists the clauses (in the form of RestrictInfos)
376 * that will be used in the merge. (Before 7.0, this was a list of bare
377 * clause expressions, but we can save on list memory and cost_qual_eval
378 * work by leaving it in the form of a RestrictInfo list.)
380 * Note that the mergeclauses are a subset of the parent relation's
381 * restriction-clause list. Any join clauses that are not mergejoinable
382 * appear only in the parent's restrict list, and must be checked by a
383 * qpqual at execution time.
385 * outersortkeys (resp. innersortkeys) is NIL if the outer path
386 * (resp. inner path) is already ordered appropriately for the
387 * mergejoin. If it is not NIL then it is a PathKeys list describing
388 * the ordering that must be created by an explicit sort step.
391 typedef struct MergePath
394 List *path_mergeclauses; /* join clauses to be used for
396 List *outersortkeys; /* keys for explicit sort, if any */
397 List *innersortkeys; /* keys for explicit sort, if any */
401 * A hashjoin path has these fields.
403 * The remarks above for mergeclauses apply for hashclauses as well.
404 * (But note that path_hashclauses will always be a one-element list,
405 * since we only hash on one hashable clause.)
407 * Hashjoin does not care what order its inputs appear in, so we have
408 * no need for sortkeys.
411 typedef struct HashPath
414 List *path_hashclauses; /* join clauses used for hashing */
418 * Restriction clause info.
420 * We create one of these for each AND sub-clause of a restriction condition
421 * (WHERE or JOIN/ON clause). Since the restriction clauses are logically
422 * ANDed, we can use any one of them or any subset of them to filter out
423 * tuples, without having to evaluate the rest. The RestrictInfo node itself
424 * stores data used by the optimizer while choosing the best query plan.
426 * If a restriction clause references a single base relation, it will appear
427 * in the baserestrictinfo list of the RelOptInfo for that base rel.
429 * If a restriction clause references more than one base rel, it will
430 * appear in the JoinInfo lists of every RelOptInfo that describes a strict
431 * subset of the base rels mentioned in the clause. The JoinInfo lists are
432 * used to drive join tree building by selecting plausible join candidates.
433 * The clause cannot actually be applied until we have built a join rel
434 * containing all the base rels it references, however.
436 * When we construct a join rel that includes all the base rels referenced
437 * in a multi-relation restriction clause, we place that clause into the
438 * joinrestrictinfo lists of paths for the join rel, if neither left nor
439 * right sub-path includes all base rels referenced in the clause. The clause
440 * will be applied at that join level, and will not propagate any further up
441 * the join tree. (Note: the "predicate migration" code was once intended to
442 * push restriction clauses up and down the plan tree based on evaluation
443 * costs, but it's dead code and is unlikely to be resurrected in the
444 * foreseeable future.)
446 * Note that in the presence of more than two rels, a multi-rel restriction
447 * might reach different heights in the join tree depending on the join
448 * sequence we use. So, these clauses cannot be associated directly with
449 * the join RelOptInfo, but must be kept track of on a per-join-path basis.
451 * When dealing with outer joins we have to be very careful about pushing qual
452 * clauses up and down the tree. An outer join's own JOIN/ON conditions must
453 * be evaluated exactly at that join node, and any quals appearing in WHERE or
454 * in a JOIN above the outer join cannot be pushed down below the outer join.
455 * Otherwise the outer join will produce wrong results because it will see the
456 * wrong sets of input rows. All quals are stored as RestrictInfo nodes
457 * during planning, but there's a flag to indicate whether a qual has been
458 * pushed down to a lower level than its original syntactic placement in the
459 * join tree would suggest. If an outer join prevents us from pushing a qual
460 * down to its "natural" semantic level (the level associated with just the
461 * base rels used in the qual) then the qual will appear in JoinInfo lists
462 * that reference more than just the base rels it actually uses. By
463 * pretending that the qual references all the rels appearing in the outer
464 * join, we prevent it from being evaluated below the outer join's joinrel.
465 * When we do form the outer join's joinrel, we still need to distinguish
466 * those quals that are actually in that join's JOIN/ON condition from those
467 * that appeared higher in the tree and were pushed down to the join rel
468 * because they used no other rels. That's what the ispusheddown flag is for;
469 * it tells us that a qual came from a point above the join of the specific
470 * set of base rels that it uses (or that the JoinInfo structures claim it
471 * uses). A clause that originally came from WHERE will *always* have its
472 * ispusheddown flag set; a clause that came from an INNER JOIN condition,
473 * but doesn't use all the rels being joined, will also have ispusheddown set
474 * because it will get attached to some lower joinrel.
476 * In general, the referenced clause might be arbitrarily complex. The
477 * kinds of clauses we can handle as indexscan quals, mergejoin clauses,
478 * or hashjoin clauses are fairly limited --- the code for each kind of
479 * path is responsible for identifying the restrict clauses it can use
480 * and ignoring the rest. Clauses not implemented by an indexscan,
481 * mergejoin, or hashjoin will be placed in the plan qual or joinqual field
482 * of the final Plan node, where they will be enforced by general-purpose
483 * qual-expression-evaluation code. (But we are still entitled to count
484 * their selectivity when estimating the result tuple count, if we
485 * can guess what it is...)
488 typedef struct RestrictInfo
492 Expr *clause; /* the represented clause of WHERE or JOIN */
494 Cost eval_cost; /* eval cost of clause; -1 if not yet set */
496 bool ispusheddown; /* TRUE if clause was pushed down in level */
498 /* only used if clause is an OR clause: */
499 List *subclauseindices; /* indexes matching subclauses */
500 /* subclauseindices is a List of Lists of IndexOptInfos */
502 /* valid if clause is mergejoinable, else InvalidOid: */
503 Oid mergejoinoperator; /* copy of clause operator */
504 Oid left_sortop; /* leftside sortop needed for mergejoin */
505 Oid right_sortop; /* rightside sortop needed for mergejoin */
507 /* cache space for mergeclause processing; NIL if not yet set */
508 List *left_pathkey; /* canonical pathkey for left side */
509 List *right_pathkey; /* canonical pathkey for right side */
511 /* valid if clause is hashjoinable, else InvalidOid: */
512 Oid hashjoinoperator; /* copy of clause operator */
514 /* cache space for hashclause processing; -1 if not yet set */
515 Selectivity left_dispersion; /* dispersion of left side */
516 Selectivity right_dispersion; /* dispersion of right side */
522 * We make a list of these for each RelOptInfo, containing info about
523 * all the join clauses this RelOptInfo participates in. (For this
524 * purpose, a "join clause" is a WHERE clause that mentions both vars
525 * belonging to this relation and vars belonging to relations not yet
526 * joined to it.) We group these clauses according to the set of
527 * other base relations (unjoined relations) mentioned in them.
528 * There is one JoinInfo for each distinct set of unjoined_relids,
529 * and its jinfo_restrictinfo lists the clause(s) that use that set
530 * of other relations.
533 typedef struct JoinInfo
536 Relids unjoined_relids; /* some rels not yet part of my RelOptInfo */
537 List *jinfo_restrictinfo; /* relevant RestrictInfos */
542 * A stream represents a root-to-leaf path in a plan tree (i.e. a tree of
543 * JoinPaths and Paths). The stream includes pointers to all Path nodes,
544 * as well as to any clauses that reside above Path nodes. This structure
545 * is used to make Path nodes and clauses look similar, so that Predicate
548 * XXX currently, Predicate Migration is dead code, and so is this node type.
549 * Probably should remove support for it.
551 * pathptr -- pointer to the current path node
552 * cinfo -- if NULL, this stream node referes to the path node.
553 * Otherwise this is a pointer to the current clause.
554 * clausetype -- whether cinfo is in loc_restrictinfo or pathinfo in the
555 * path node (XXX this is now used only by dead code, which is
556 * good because the distinction no longer exists...)
557 * upstream -- linked list pointer upwards
558 * downstream -- ditto, downwards
559 * groupup -- whether or not this node is in a group with the node upstream
560 * groupcost -- total cost of the group that node is in
561 * groupsel -- total selectivity of the group that node is in
563 typedef struct Stream *StreamPtr;
565 typedef struct Stream
572 StreamPtr downstream;
575 Selectivity groupsel;
578 #endif /* RELATION_H */