1 /*-------------------------------------------------------------------------
4 * Definitions for planner's internal data structures.
7 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
8 * Portions Copyright (c) 1994, Regents of the University of California
10 * $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.173 2009/06/11 14:49:11 momjian Exp $
12 *-------------------------------------------------------------------------
17 #include "access/sdir.h"
18 #include "nodes/bitmapset.h"
19 #include "nodes/params.h"
20 #include "nodes/parsenodes.h"
21 #include "storage/block.h"
26 * Set of relation identifiers (indexes into the rangetable).
28 typedef Bitmapset *Relids;
31 * When looking for a "cheapest path", this enum specifies whether we want
32 * cheapest startup cost or cheapest total cost.
34 typedef enum CostSelector
36 STARTUP_COST, TOTAL_COST
40 * The cost estimate produced by cost_qual_eval() includes both a one-time
41 * (startup) cost, and a per-tuple cost.
43 typedef struct QualCost
45 Cost startup; /* one-time cost */
46 Cost per_tuple; /* per-evaluation cost */
52 * Global information for planning/optimization
54 * PlannerGlobal holds state for an entire planner invocation; this state
55 * is shared across all levels of sub-Queries that exist in the command being
59 typedef struct PlannerGlobal
63 ParamListInfo boundParams; /* Param values provided to planner() */
65 List *paramlist; /* to keep track of cross-level Params */
67 List *subplans; /* Plans for SubPlan nodes */
69 List *subrtables; /* Rangetables for SubPlan nodes */
71 Bitmapset *rewindPlanIDs; /* indices of subplans that require REWIND */
73 List *finalrtable; /* "flat" rangetable for executor */
75 List *relationOids; /* OIDs of relations the plan depends on */
77 List *invalItems; /* other dependencies, as PlanInvalItems */
79 Index lastPHId; /* highest PlaceHolderVar ID assigned */
81 bool transientPlan; /* redo plan when TransactionXmin changes? */
84 /* macro for fetching the Plan associated with a SubPlan node */
85 #define planner_subplan_get_plan(root, subplan) \
86 ((Plan *) list_nth((root)->glob->subplans, (subplan)->plan_id - 1))
91 * Per-query information for planning/optimization
93 * This struct is conventionally called "root" in all the planner routines.
94 * It holds links to all of the planner's working state, in addition to the
95 * original Query. Note that at present the planner extensively modifies
96 * the passed-in Query data structure; someday that should stop.
99 typedef struct PlannerInfo
103 Query *parse; /* the Query being planned */
105 PlannerGlobal *glob; /* global info for current planner run */
107 Index query_level; /* 1 at the outermost Query */
109 struct PlannerInfo *parent_root; /* NULL at outermost Query */
112 * simple_rel_array holds pointers to "base rels" and "other rels" (see
113 * comments for RelOptInfo for more info). It is indexed by rangetable
114 * index (so entry 0 is always wasted). Entries can be NULL when an RTE
115 * does not correspond to a base relation, such as a join RTE or an
116 * unreferenced view RTE; or if the RelOptInfo hasn't been made yet.
118 struct RelOptInfo **simple_rel_array; /* All 1-rel RelOptInfos */
119 int simple_rel_array_size; /* allocated size of array */
122 * simple_rte_array is the same length as simple_rel_array and holds
123 * pointers to the associated rangetable entries. This lets us avoid
124 * rt_fetch(), which can be a bit slow once large inheritance sets have
127 RangeTblEntry **simple_rte_array; /* rangetable as an array */
130 * join_rel_list is a list of all join-relation RelOptInfos we have
131 * considered in this planning run. For small problems we just scan the
132 * list to do lookups, but when there are many join relations we build a
133 * hash table for faster lookups. The hash table is present and valid
134 * when join_rel_hash is not NULL. Note that we still maintain the list
135 * even when using the hash table for lookups; this simplifies life for
138 List *join_rel_list; /* list of join-relation RelOptInfos */
139 struct HTAB *join_rel_hash; /* optional hashtable for join relations */
141 List *resultRelations; /* integer list of RT indexes, or NIL */
143 List *returningLists; /* list of lists of TargetEntry, or NIL */
145 List *init_plans; /* init SubPlans for query */
147 List *cte_plan_ids; /* per-CTE-item list of subplan IDs */
149 List *eq_classes; /* list of active EquivalenceClasses */
151 List *canon_pathkeys; /* list of "canonical" PathKeys */
153 List *left_join_clauses; /* list of RestrictInfos for
154 * mergejoinable outer join clauses
155 * w/nonnullable var on left */
157 List *right_join_clauses; /* list of RestrictInfos for
158 * mergejoinable outer join clauses
159 * w/nonnullable var on right */
161 List *full_join_clauses; /* list of RestrictInfos for
162 * mergejoinable full join clauses */
164 List *join_info_list; /* list of SpecialJoinInfos */
166 List *append_rel_list; /* list of AppendRelInfos */
168 List *placeholder_list; /* list of PlaceHolderInfos */
170 List *query_pathkeys; /* desired pathkeys for query_planner(), and
171 * actual pathkeys afterwards */
173 List *group_pathkeys; /* groupClause pathkeys, if any */
174 List *window_pathkeys; /* pathkeys of bottom window, if any */
175 List *distinct_pathkeys; /* distinctClause pathkeys, if any */
176 List *sort_pathkeys; /* sortClause pathkeys, if any */
178 List *initial_rels; /* RelOptInfos we are now trying to join */
180 MemoryContext planner_cxt; /* context holding PlannerInfo */
182 double total_table_pages; /* # of pages in all tables of query */
184 double tuple_fraction; /* tuple_fraction passed to query_planner */
186 bool hasJoinRTEs; /* true if any RTEs are RTE_JOIN kind */
187 bool hasHavingQual; /* true if havingQual was non-null */
188 bool hasPseudoConstantQuals; /* true if any RestrictInfo has
189 * pseudoconstant = true */
190 bool hasRecursion; /* true if planning a recursive WITH item */
192 /* These fields are used only when hasRecursion is true: */
193 int wt_param_id; /* PARAM_EXEC ID for the work table */
194 struct Plan *non_recursive_plan; /* plan for non-recursive term */
199 * In places where it's known that simple_rte_array[] must have been prepared
200 * already, we just index into it to fetch RTEs. In code that might be
201 * executed before or after entering query_planner(), use this macro.
203 #define planner_rt_fetch(rti, root) \
204 ((root)->simple_rte_array ? (root)->simple_rte_array[rti] : \
205 rt_fetch(rti, (root)->parse->rtable))
210 * Per-relation information for planning/optimization
212 * For planning purposes, a "base rel" is either a plain relation (a table)
213 * or the output of a sub-SELECT or function that appears in the range table.
214 * In either case it is uniquely identified by an RT index. A "joinrel"
215 * is the joining of two or more base rels. A joinrel is identified by
216 * the set of RT indexes for its component baserels. We create RelOptInfo
217 * nodes for each baserel and joinrel, and store them in the PlannerInfo's
218 * simple_rel_array and join_rel_list respectively.
220 * Note that there is only one joinrel for any given set of component
221 * baserels, no matter what order we assemble them in; so an unordered
222 * set is the right datatype to identify it with.
224 * We also have "other rels", which are like base rels in that they refer to
225 * single RT indexes; but they are not part of the join tree, and are given
226 * a different RelOptKind to identify them.
228 * Currently the only kind of otherrels are those made for member relations
229 * of an "append relation", that is an inheritance set or UNION ALL subquery.
230 * An append relation has a parent RTE that is a base rel, which represents
231 * the entire append relation. The member RTEs are otherrels. The parent
232 * is present in the query join tree but the members are not. The member
233 * RTEs and otherrels are used to plan the scans of the individual tables or
234 * subqueries of the append set; then the parent baserel is given an Append
235 * plan comprising the best plans for the individual member rels. (See
236 * comments for AppendRelInfo for more information.)
238 * At one time we also made otherrels to represent join RTEs, for use in
239 * handling join alias Vars. Currently this is not needed because all join
240 * alias Vars are expanded to non-aliased form during preprocess_expression.
242 * Parts of this data structure are specific to various scan and join
243 * mechanisms. It didn't seem worth creating new node types for them.
245 * relids - Set of base-relation identifiers; it is a base relation
246 * if there is just one, a join relation if more than one
247 * rows - estimated number of tuples in the relation after restriction
248 * clauses have been applied (ie, output rows of a plan for it)
249 * width - avg. number of bytes per tuple in the relation after the
250 * appropriate projections have been done (ie, output width)
251 * reltargetlist - List of Var and PlaceHolderVar nodes for the values
252 * we need to output from this relation.
253 * List is in no particular order, but all rels of an
254 * appendrel set must use corresponding orders.
255 * NOTE: in a child relation, may contain RowExpr or
256 * ConvertRowtypeExpr representing a whole-row Var.
257 * pathlist - List of Path nodes, one for each potentially useful
258 * method of generating the relation
259 * cheapest_startup_path - the pathlist member with lowest startup cost
260 * (regardless of its ordering)
261 * cheapest_total_path - the pathlist member with lowest total cost
262 * (regardless of its ordering)
263 * cheapest_unique_path - for caching cheapest path to produce unique
264 * (no duplicates) output from relation
266 * If the relation is a base relation it will have these fields set:
268 * relid - RTE index (this is redundant with the relids field, but
269 * is provided for convenience of access)
270 * rtekind - distinguishes plain relation, subquery, or function RTE
271 * min_attr, max_attr - range of valid AttrNumbers for rel
272 * attr_needed - array of bitmapsets indicating the highest joinrel
273 * in which each attribute is needed; if bit 0 is set then
274 * the attribute is needed as part of final targetlist
275 * attr_widths - cache space for per-attribute width estimates;
276 * zero means not computed yet
277 * indexlist - list of IndexOptInfo nodes for relation's indexes
278 * (always NIL if it's not a table)
279 * pages - number of disk pages in relation (zero if not a table)
280 * tuples - number of tuples in relation (not considering restrictions)
281 * subplan - plan for subquery (NULL if it's not a subquery)
282 * subrtable - rangetable for subquery (NIL if it's not a subquery)
284 * Note: for a subquery, tuples and subplan are not set immediately
285 * upon creation of the RelOptInfo object; they are filled in when
286 * set_base_rel_pathlist processes the object.
288 * For otherrels that are appendrel members, these fields are filled
289 * in just as for a baserel.
291 * The presence of the remaining fields depends on the restrictions
292 * and joins that the relation participates in:
294 * baserestrictinfo - List of RestrictInfo nodes, containing info about
295 * each non-join qualification clause in which this relation
296 * participates (only used for base rels)
297 * baserestrictcost - Estimated cost of evaluating the baserestrictinfo
298 * clauses at a single tuple (only used for base rels)
299 * joininfo - List of RestrictInfo nodes, containing info about each
300 * join clause in which this relation participates (but
301 * note this excludes clauses that might be derivable from
302 * EquivalenceClasses)
303 * has_eclass_joins - flag that EquivalenceClass joins are possible
304 * index_outer_relids - only used for base rels; set of outer relids
305 * that participate in indexable joinclauses for this rel
306 * index_inner_paths - only used for base rels; list of InnerIndexscanInfo
307 * nodes showing best indexpaths for various subsets of
308 * index_outer_relids.
310 * Note: Keeping a restrictinfo list in the RelOptInfo is useful only for
311 * base rels, because for a join rel the set of clauses that are treated as
312 * restrict clauses varies depending on which sub-relations we choose to join.
313 * (For example, in a 3-base-rel join, a clause relating rels 1 and 2 must be
314 * treated as a restrictclause if we join {1} and {2 3} to make {1 2 3}; but
315 * if we join {1 2} and {3} then that clause will be a restrictclause in {1 2}
316 * and should not be processed again at the level of {1 2 3}.) Therefore,
317 * the restrictinfo list in the join case appears in individual JoinPaths
318 * (field joinrestrictinfo), not in the parent relation. But it's OK for
319 * the RelOptInfo to store the joininfo list, because that is the same
320 * for a given rel no matter how we form it.
322 * We store baserestrictcost in the RelOptInfo (for base relations) because
323 * we know we will need it at least once (to price the sequential scan)
324 * and may need it multiple times to price index scans.
327 typedef enum RelOptKind
331 RELOPT_OTHER_MEMBER_REL
334 typedef struct RelOptInfo
338 RelOptKind reloptkind;
340 /* all relations included in this RelOptInfo */
341 Relids relids; /* set of base relids (rangetable indexes) */
343 /* size estimates generated by planner */
344 double rows; /* estimated number of result tuples */
345 int width; /* estimated avg width of result tuples */
347 /* materialization information */
348 List *reltargetlist; /* Vars to be output by scan of relation */
349 List *pathlist; /* Path structures */
350 struct Path *cheapest_startup_path;
351 struct Path *cheapest_total_path;
352 struct Path *cheapest_unique_path;
354 /* information about a base rel (not set for join rels!) */
356 RTEKind rtekind; /* RELATION, SUBQUERY, or FUNCTION */
357 AttrNumber min_attr; /* smallest attrno of rel (often <0) */
358 AttrNumber max_attr; /* largest attrno of rel */
359 Relids *attr_needed; /* array indexed [min_attr .. max_attr] */
360 int32 *attr_widths; /* array indexed [min_attr .. max_attr] */
361 List *indexlist; /* list of IndexOptInfo */
364 struct Plan *subplan; /* if subquery */
365 List *subrtable; /* if subquery */
367 /* used by various scans and joins: */
368 List *baserestrictinfo; /* RestrictInfo structures (if base
370 QualCost baserestrictcost; /* cost of evaluating the above */
371 List *joininfo; /* RestrictInfo structures for join clauses
372 * involving this rel */
373 bool has_eclass_joins; /* T means joininfo is incomplete */
375 /* cached info about inner indexscan paths for relation: */
376 Relids index_outer_relids; /* other relids in indexable join
378 List *index_inner_paths; /* InnerIndexscanInfo nodes */
381 * Inner indexscans are not in the main pathlist because they are not
382 * usable except in specific join contexts. We use the index_inner_paths
383 * list just to avoid recomputing the best inner indexscan repeatedly for
384 * similar outer relations. See comments for InnerIndexscanInfo.
390 * Per-index information for planning/optimization
392 * Prior to Postgres 7.0, RelOptInfo was used to describe both relations
393 * and indexes, but that created confusion without actually doing anything
394 * useful. So now we have a separate IndexOptInfo struct for indexes.
396 * opfamily[], indexkeys[], opcintype[], fwdsortop[], revsortop[],
397 * and nulls_first[] each have ncolumns entries.
398 * Note: for historical reasons, the opfamily array has an extra entry
399 * that is always zero. Some code scans until it sees a zero entry,
400 * rather than looking at ncolumns.
402 * Zeroes in the indexkeys[] array indicate index columns that are
403 * expressions; there is one element in indexprs for each such column.
405 * For an unordered index, the sortop arrays contains zeroes. Note that
406 * fwdsortop[] and nulls_first[] describe the sort ordering of a forward
407 * indexscan; we can also consider a backward indexscan, which will
408 * generate sort order described by revsortop/!nulls_first.
410 * The indexprs and indpred expressions have been run through
411 * prepqual.c and eval_const_expressions() for ease of matching to
412 * WHERE clauses. indpred is in implicit-AND form.
414 typedef struct IndexOptInfo
418 Oid indexoid; /* OID of the index relation */
419 RelOptInfo *rel; /* back-link to index's table */
421 /* statistics from pg_class */
422 BlockNumber pages; /* number of disk pages in index */
423 double tuples; /* number of index tuples in index */
425 /* index descriptor information */
426 int ncolumns; /* number of columns in index */
427 Oid *opfamily; /* OIDs of operator families for columns */
428 int *indexkeys; /* column numbers of index's keys, or 0 */
429 Oid *opcintype; /* OIDs of opclass declared input data types */
430 Oid *fwdsortop; /* OIDs of sort operators for each column */
431 Oid *revsortop; /* OIDs of sort operators for backward scan */
432 bool *nulls_first; /* do NULLs come first in the sort order? */
433 Oid relam; /* OID of the access method (in pg_am) */
435 RegProcedure amcostestimate; /* OID of the access method's cost fcn */
437 List *indexprs; /* expressions for non-simple index columns */
438 List *indpred; /* predicate if a partial index, else NIL */
440 bool predOK; /* true if predicate matches query */
441 bool unique; /* true if a unique index */
442 bool amoptionalkey; /* can query omit key for the first column? */
443 bool amsearchnulls; /* can AM search for NULL index entries? */
444 bool amhasgettuple; /* does AM have amgettuple interface? */
445 bool amhasgetbitmap; /* does AM have amgetbitmap interface? */
452 * Whenever we can determine that a mergejoinable equality clause A = B is
453 * not delayed by any outer join, we create an EquivalenceClass containing
454 * the expressions A and B to record this knowledge. If we later find another
455 * equivalence B = C, we add C to the existing EquivalenceClass; this may
456 * require merging two existing EquivalenceClasses. At the end of the qual
457 * distribution process, we have sets of values that are known all transitively
458 * equal to each other, where "equal" is according to the rules of the btree
459 * operator family(s) shown in ec_opfamilies. (We restrict an EC to contain
460 * only equalities whose operators belong to the same set of opfamilies. This
461 * could probably be relaxed, but for now it's not worth the trouble, since
462 * nearly all equality operators belong to only one btree opclass anyway.)
464 * We also use EquivalenceClasses as the base structure for PathKeys, letting
465 * us represent knowledge about different sort orderings being equivalent.
466 * Since every PathKey must reference an EquivalenceClass, we will end up
467 * with single-member EquivalenceClasses whenever a sort key expression has
468 * not been equivalenced to anything else. It is also possible that such an
469 * EquivalenceClass will contain a volatile expression ("ORDER BY random()"),
470 * which is a case that can't arise otherwise since clauses containing
471 * volatile functions are never considered mergejoinable. We mark such
472 * EquivalenceClasses specially to prevent them from being merged with
473 * ordinary EquivalenceClasses. Also, for volatile expressions we have
474 * to be careful to match the EquivalenceClass to the correct targetlist
475 * entry: consider SELECT random() AS a, random() AS b ... ORDER BY b,a.
476 * So we record the SortGroupRef of the originating sort clause.
478 * We allow equality clauses appearing below the nullable side of an outer join
479 * to form EquivalenceClasses, but these have a slightly different meaning:
480 * the included values might be all NULL rather than all the same non-null
481 * values. See src/backend/optimizer/README for more on that point.
483 * NB: if ec_merged isn't NULL, this class has been merged into another, and
484 * should be ignored in favor of using the pointed-to class.
486 typedef struct EquivalenceClass
490 List *ec_opfamilies; /* btree operator family OIDs */
491 List *ec_members; /* list of EquivalenceMembers */
492 List *ec_sources; /* list of generating RestrictInfos */
493 List *ec_derives; /* list of derived RestrictInfos */
494 Relids ec_relids; /* all relids appearing in ec_members */
495 bool ec_has_const; /* any pseudoconstants in ec_members? */
496 bool ec_has_volatile; /* the (sole) member is a volatile expr */
497 bool ec_below_outer_join; /* equivalence applies below an OJ */
498 bool ec_broken; /* failed to generate needed clauses? */
499 Index ec_sortref; /* originating sortclause label, or 0 */
500 struct EquivalenceClass *ec_merged; /* set if merged into another EC */
504 * If an EC contains a const and isn't below-outer-join, any PathKey depending
505 * on it must be redundant, since there's only one possible value of the key.
507 #define EC_MUST_BE_REDUNDANT(eclass) \
508 ((eclass)->ec_has_const && !(eclass)->ec_below_outer_join)
511 * EquivalenceMember - one member expression of an EquivalenceClass
513 * em_is_child signifies that this element was built by transposing a member
514 * for an inheritance parent relation to represent the corresponding expression
515 * on an inheritance child. The element should be ignored for all purposes
516 * except constructing inner-indexscan paths for the child relation. (Other
517 * types of join are driven from transposed joininfo-list entries.) Note
518 * that the EC's ec_relids field does NOT include the child relation.
520 * em_datatype is usually the same as exprType(em_expr), but can be
521 * different when dealing with a binary-compatible opfamily; in particular
522 * anyarray_ops would never work without this. Use em_datatype when
523 * looking up a specific btree operator to work with this expression.
525 typedef struct EquivalenceMember
529 Expr *em_expr; /* the expression represented */
530 Relids em_relids; /* all relids appearing in em_expr */
531 bool em_is_const; /* expression is pseudoconstant? */
532 bool em_is_child; /* derived version for a child relation? */
533 Oid em_datatype; /* the "nominal type" used by the opfamily */
539 * The sort ordering of a path is represented by a list of PathKey nodes.
540 * An empty list implies no known ordering. Otherwise the first item
541 * represents the primary sort key, the second the first secondary sort key,
542 * etc. The value being sorted is represented by linking to an
543 * EquivalenceClass containing that value and including pk_opfamily among its
544 * ec_opfamilies. This is a convenient method because it makes it trivial
545 * to detect equivalent and closely-related orderings. (See optimizer/README
546 * for more information.)
548 * Note: pk_strategy is either BTLessStrategyNumber (for ASC) or
549 * BTGreaterStrategyNumber (for DESC). We assume that all ordering-capable
550 * index types will use btree-compatible strategy numbers.
553 typedef struct PathKey
557 EquivalenceClass *pk_eclass; /* the value that is ordered */
558 Oid pk_opfamily; /* btree opfamily defining the ordering */
559 int pk_strategy; /* sort direction (ASC or DESC) */
560 bool pk_nulls_first; /* do NULLs come before normal values? */
564 * Type "Path" is used as-is for sequential-scan paths, as well as some other
565 * simple plan types that we don't need any extra information in the path for.
566 * For other path types it is the first component of a larger struct.
568 * Note: "pathtype" is the NodeTag of the Plan node we could build from this
569 * Path. It is partially redundant with the Path's NodeTag, but allows us
570 * to use the same Path type for multiple Plan types where there is no need
571 * to distinguish the Plan type during path processing.
578 NodeTag pathtype; /* tag identifying scan/join method */
580 RelOptInfo *parent; /* the relation this path can build */
582 /* estimated execution costs for path (see costsize.c for more info) */
583 Cost startup_cost; /* cost expended before fetching any tuples */
584 Cost total_cost; /* total cost (assuming all tuples fetched) */
586 List *pathkeys; /* sort ordering of path's output */
587 /* pathkeys is a List of PathKey nodes; see above */
591 * IndexPath represents an index scan over a single index.
593 * 'indexinfo' is the index to be scanned.
595 * 'indexclauses' is a list of index qualification clauses, with implicit
596 * AND semantics across the list. Each clause is a RestrictInfo node from
597 * the query's WHERE or JOIN conditions.
599 * 'indexquals' has the same structure as 'indexclauses', but it contains
600 * the actual indexqual conditions that can be used with the index.
601 * In simple cases this is identical to 'indexclauses', but when special
602 * indexable operators appear in 'indexclauses', they are replaced by the
603 * derived indexscannable conditions in 'indexquals'.
605 * 'isjoininner' is TRUE if the path is a nestloop inner scan (that is,
606 * some of the index conditions are join rather than restriction clauses).
607 * Note that the path costs will be calculated differently from a plain
608 * indexscan in this case, and in addition there's a special 'rows' value
609 * different from the parent RelOptInfo's (see below).
611 * 'indexscandir' is one of:
612 * ForwardScanDirection: forward scan of an ordered index
613 * BackwardScanDirection: backward scan of an ordered index
614 * NoMovementScanDirection: scan of an unordered index, or don't care
615 * (The executor doesn't care whether it gets ForwardScanDirection or
616 * NoMovementScanDirection for an indexscan, but the planner wants to
617 * distinguish ordered from unordered indexes for building pathkeys.)
619 * 'indextotalcost' and 'indexselectivity' are saved in the IndexPath so that
620 * we need not recompute them when considering using the same index in a
621 * bitmap index/heap scan (see BitmapHeapPath). The costs of the IndexPath
622 * itself represent the costs of an IndexScan plan type.
624 * 'rows' is the estimated result tuple count for the indexscan. This
625 * is the same as path.parent->rows for a simple indexscan, but it is
626 * different for a nestloop inner scan, because the additional indexquals
627 * coming from join clauses make the scan more selective than the parent
628 * rel's restrict clauses alone would do.
631 typedef struct IndexPath
634 IndexOptInfo *indexinfo;
638 ScanDirection indexscandir;
640 Selectivity indexselectivity;
641 double rows; /* estimated number of result tuples */
645 * BitmapHeapPath represents one or more indexscans that generate TID bitmaps
646 * instead of directly accessing the heap, followed by AND/OR combinations
647 * to produce a single bitmap, followed by a heap scan that uses the bitmap.
648 * Note that the output is always considered unordered, since it will come
649 * out in physical heap order no matter what the underlying indexes did.
651 * The individual indexscans are represented by IndexPath nodes, and any
652 * logic on top of them is represented by a tree of BitmapAndPath and
653 * BitmapOrPath nodes. Notice that we can use the same IndexPath node both
654 * to represent a regular IndexScan plan, and as the child of a BitmapHeapPath
655 * that represents scanning the same index using a BitmapIndexScan. The
656 * startup_cost and total_cost figures of an IndexPath always represent the
657 * costs to use it as a regular IndexScan. The costs of a BitmapIndexScan
658 * can be computed using the IndexPath's indextotalcost and indexselectivity.
660 * BitmapHeapPaths can be nestloop inner indexscans. The isjoininner and
661 * rows fields serve the same purpose as for plain IndexPaths.
663 typedef struct BitmapHeapPath
666 Path *bitmapqual; /* IndexPath, BitmapAndPath, BitmapOrPath */
667 bool isjoininner; /* T if it's a nestloop inner scan */
668 double rows; /* estimated number of result tuples */
672 * BitmapAndPath represents a BitmapAnd plan node; it can only appear as
673 * part of the substructure of a BitmapHeapPath. The Path structure is
674 * a bit more heavyweight than we really need for this, but for simplicity
675 * we make it a derivative of Path anyway.
677 typedef struct BitmapAndPath
680 List *bitmapquals; /* IndexPaths and BitmapOrPaths */
681 Selectivity bitmapselectivity;
685 * BitmapOrPath represents a BitmapOr plan node; it can only appear as
686 * part of the substructure of a BitmapHeapPath. The Path structure is
687 * a bit more heavyweight than we really need for this, but for simplicity
688 * we make it a derivative of Path anyway.
690 typedef struct BitmapOrPath
693 List *bitmapquals; /* IndexPaths and BitmapAndPaths */
694 Selectivity bitmapselectivity;
698 * TidPath represents a scan by TID
700 * tidquals is an implicitly OR'ed list of qual expressions of the form
701 * "CTID = pseudoconstant" or "CTID = ANY(pseudoconstant_array)".
702 * Note they are bare expressions, not RestrictInfos.
704 typedef struct TidPath
707 List *tidquals; /* qual(s) involving CTID = something */
711 * AppendPath represents an Append plan, ie, successive execution of
712 * several member plans.
714 * Note: it is possible for "subpaths" to contain only one, or even no,
715 * elements. These cases are optimized during create_append_plan.
716 * In particular, an AppendPath with no subpaths is a "dummy" path that
717 * is created to represent the case that a relation is provably empty.
719 typedef struct AppendPath
722 List *subpaths; /* list of component Paths */
725 #define IS_DUMMY_PATH(p) \
726 (IsA((p), AppendPath) && ((AppendPath *) (p))->subpaths == NIL)
729 * ResultPath represents use of a Result plan node to compute a variable-free
730 * targetlist with no underlying tables (a "SELECT expressions" query).
731 * The query could have a WHERE clause, too, represented by "quals".
733 * Note that quals is a list of bare clauses, not RestrictInfos.
735 typedef struct ResultPath
742 * MaterialPath represents use of a Material plan node, i.e., caching of
743 * the output of its subpath. This is used when the subpath is expensive
744 * and needs to be scanned repeatedly, or when we need mark/restore ability
745 * and the subpath doesn't have it.
747 typedef struct MaterialPath
754 * UniquePath represents elimination of distinct rows from the output of
757 * This is unlike the other Path nodes in that it can actually generate
758 * different plans: either hash-based or sort-based implementation, or a
759 * no-op if the input path can be proven distinct already. The decision
760 * is sufficiently localized that it's not worth having separate Path node
761 * types. (Note: in the no-op case, we could eliminate the UniquePath node
762 * entirely and just return the subpath; but it's convenient to have a
763 * UniquePath in the path tree to signal upper-level routines that the input
764 * is known distinct.)
768 UNIQUE_PATH_NOOP, /* input is known unique already */
769 UNIQUE_PATH_HASH, /* use hashing */
770 UNIQUE_PATH_SORT /* use sorting */
773 typedef struct UniquePath
777 UniquePathMethod umethod;
778 List *in_operators; /* equality operators of the IN clause */
779 List *uniq_exprs; /* expressions to be made unique */
780 double rows; /* estimated number of result tuples */
784 * All join-type paths share these fields.
787 typedef struct JoinPath
793 Path *outerjoinpath; /* path for the outer side of the join */
794 Path *innerjoinpath; /* path for the inner side of the join */
796 List *joinrestrictinfo; /* RestrictInfos to apply to join */
799 * See the notes for RelOptInfo to understand why joinrestrictinfo is
800 * needed in JoinPath, and can't be merged into the parent RelOptInfo.
805 * A nested-loop path needs no special fields.
808 typedef JoinPath NestPath;
811 * A mergejoin path has these fields.
813 * path_mergeclauses lists the clauses (in the form of RestrictInfos)
814 * that will be used in the merge.
816 * Note that the mergeclauses are a subset of the parent relation's
817 * restriction-clause list. Any join clauses that are not mergejoinable
818 * appear only in the parent's restrict list, and must be checked by a
819 * qpqual at execution time.
821 * outersortkeys (resp. innersortkeys) is NIL if the outer path
822 * (resp. inner path) is already ordered appropriately for the
823 * mergejoin. If it is not NIL then it is a PathKeys list describing
824 * the ordering that must be created by an explicit sort step.
827 typedef struct MergePath
830 List *path_mergeclauses; /* join clauses to be used for merge */
831 List *outersortkeys; /* keys for explicit sort, if any */
832 List *innersortkeys; /* keys for explicit sort, if any */
836 * A hashjoin path has these fields.
838 * The remarks above for mergeclauses apply for hashclauses as well.
840 * Hashjoin does not care what order its inputs appear in, so we have
841 * no need for sortkeys.
844 typedef struct HashPath
847 List *path_hashclauses; /* join clauses used for hashing */
848 int num_batches; /* number of batches expected */
852 * Restriction clause info.
854 * We create one of these for each AND sub-clause of a restriction condition
855 * (WHERE or JOIN/ON clause). Since the restriction clauses are logically
856 * ANDed, we can use any one of them or any subset of them to filter out
857 * tuples, without having to evaluate the rest. The RestrictInfo node itself
858 * stores data used by the optimizer while choosing the best query plan.
860 * If a restriction clause references a single base relation, it will appear
861 * in the baserestrictinfo list of the RelOptInfo for that base rel.
863 * If a restriction clause references more than one base rel, it will
864 * appear in the joininfo list of every RelOptInfo that describes a strict
865 * subset of the base rels mentioned in the clause. The joininfo lists are
866 * used to drive join tree building by selecting plausible join candidates.
867 * The clause cannot actually be applied until we have built a join rel
868 * containing all the base rels it references, however.
870 * When we construct a join rel that includes all the base rels referenced
871 * in a multi-relation restriction clause, we place that clause into the
872 * joinrestrictinfo lists of paths for the join rel, if neither left nor
873 * right sub-path includes all base rels referenced in the clause. The clause
874 * will be applied at that join level, and will not propagate any further up
875 * the join tree. (Note: the "predicate migration" code was once intended to
876 * push restriction clauses up and down the plan tree based on evaluation
877 * costs, but it's dead code and is unlikely to be resurrected in the
878 * foreseeable future.)
880 * Note that in the presence of more than two rels, a multi-rel restriction
881 * might reach different heights in the join tree depending on the join
882 * sequence we use. So, these clauses cannot be associated directly with
883 * the join RelOptInfo, but must be kept track of on a per-join-path basis.
885 * RestrictInfos that represent equivalence conditions (i.e., mergejoinable
886 * equalities that are not outerjoin-delayed) are handled a bit differently.
887 * Initially we attach them to the EquivalenceClasses that are derived from
888 * them. When we construct a scan or join path, we look through all the
889 * EquivalenceClasses and generate derived RestrictInfos representing the
890 * minimal set of conditions that need to be checked for this particular scan
891 * or join to enforce that all members of each EquivalenceClass are in fact
892 * equal in all rows emitted by the scan or join.
894 * When dealing with outer joins we have to be very careful about pushing qual
895 * clauses up and down the tree. An outer join's own JOIN/ON conditions must
896 * be evaluated exactly at that join node, unless they are "degenerate"
897 * conditions that reference only Vars from the nullable side of the join.
898 * Quals appearing in WHERE or in a JOIN above the outer join cannot be pushed
899 * down below the outer join, if they reference any nullable Vars.
900 * RestrictInfo nodes contain a flag to indicate whether a qual has been
901 * pushed down to a lower level than its original syntactic placement in the
902 * join tree would suggest. If an outer join prevents us from pushing a qual
903 * down to its "natural" semantic level (the level associated with just the
904 * base rels used in the qual) then we mark the qual with a "required_relids"
905 * value including more than just the base rels it actually uses. By
906 * pretending that the qual references all the rels required to form the outer
907 * join, we prevent it from being evaluated below the outer join's joinrel.
908 * When we do form the outer join's joinrel, we still need to distinguish
909 * those quals that are actually in that join's JOIN/ON condition from those
910 * that appeared elsewhere in the tree and were pushed down to the join rel
911 * because they used no other rels. That's what the is_pushed_down flag is
912 * for; it tells us that a qual is not an OUTER JOIN qual for the set of base
913 * rels listed in required_relids. A clause that originally came from WHERE
914 * or an INNER JOIN condition will *always* have its is_pushed_down flag set.
915 * It's possible for an OUTER JOIN clause to be marked is_pushed_down too,
916 * if we decide that it can be pushed down into the nullable side of the join.
917 * In that case it acts as a plain filter qual for wherever it gets evaluated.
918 * (In short, is_pushed_down is only false for non-degenerate outer join
919 * conditions. Possibly we should rename it to reflect that meaning?)
921 * RestrictInfo nodes also contain an outerjoin_delayed flag, which is true
922 * if the clause's applicability must be delayed due to any outer joins
923 * appearing below it (ie, it has to be postponed to some join level higher
924 * than the set of relations it actually references). There is also a
925 * nullable_relids field, which is the set of rels it references that can be
926 * forced null by some outer join below the clause. outerjoin_delayed = true
927 * is subtly different from nullable_relids != NULL: a clause might reference
928 * some nullable rels and yet not be outerjoin_delayed because it also
929 * references all the other rels of the outer join(s). A clause that is not
930 * outerjoin_delayed can be enforced anywhere it is computable.
932 * In general, the referenced clause might be arbitrarily complex. The
933 * kinds of clauses we can handle as indexscan quals, mergejoin clauses,
934 * or hashjoin clauses are limited (e.g., no volatile functions). The code
935 * for each kind of path is responsible for identifying the restrict clauses
936 * it can use and ignoring the rest. Clauses not implemented by an indexscan,
937 * mergejoin, or hashjoin will be placed in the plan qual or joinqual field
938 * of the finished Plan node, where they will be enforced by general-purpose
939 * qual-expression-evaluation code. (But we are still entitled to count
940 * their selectivity when estimating the result tuple count, if we
941 * can guess what it is...)
943 * When the referenced clause is an OR clause, we generate a modified copy
944 * in which additional RestrictInfo nodes are inserted below the top-level
945 * OR/AND structure. This is a convenience for OR indexscan processing:
946 * indexquals taken from either the top level or an OR subclause will have
947 * associated RestrictInfo nodes.
949 * The can_join flag is set true if the clause looks potentially useful as
950 * a merge or hash join clause, that is if it is a binary opclause with
951 * nonoverlapping sets of relids referenced in the left and right sides.
952 * (Whether the operator is actually merge or hash joinable isn't checked,
955 * The pseudoconstant flag is set true if the clause contains no Vars of
956 * the current query level and no volatile functions. Such a clause can be
957 * pulled out and used as a one-time qual in a gating Result node. We keep
958 * pseudoconstant clauses in the same lists as other RestrictInfos so that
959 * the regular clause-pushing machinery can assign them to the correct join
960 * level, but they need to be treated specially for cost and selectivity
961 * estimates. Note that a pseudoconstant clause can never be an indexqual
962 * or merge or hash join clause, so it's of no interest to large parts of
965 * When join clauses are generated from EquivalenceClasses, there may be
966 * several equally valid ways to enforce join equivalence, of which we need
967 * apply only one. We mark clauses of this kind by setting parent_ec to
968 * point to the generating EquivalenceClass. Multiple clauses with the same
969 * parent_ec in the same join are redundant.
972 typedef struct RestrictInfo
976 Expr *clause; /* the represented clause of WHERE or JOIN */
978 bool is_pushed_down; /* TRUE if clause was pushed down in level */
980 bool outerjoin_delayed; /* TRUE if delayed by lower outer join */
982 bool can_join; /* see comment above */
984 bool pseudoconstant; /* see comment above */
986 /* The set of relids (varnos) actually referenced in the clause: */
987 Relids clause_relids;
989 /* The set of relids required to evaluate the clause: */
990 Relids required_relids;
992 /* The relids used in the clause that are nullable by lower outer joins: */
993 Relids nullable_relids;
995 /* These fields are set for any binary opclause: */
996 Relids left_relids; /* relids in left side of clause */
997 Relids right_relids; /* relids in right side of clause */
999 /* This field is NULL unless clause is an OR clause: */
1000 Expr *orclause; /* modified clause with RestrictInfos */
1002 /* This field is NULL unless clause is potentially redundant: */
1003 EquivalenceClass *parent_ec; /* generating EquivalenceClass */
1005 /* cache space for cost and selectivity */
1006 QualCost eval_cost; /* eval cost of clause; -1 if not yet set */
1007 Selectivity norm_selec; /* selectivity for "normal" (JOIN_INNER)
1008 * semantics; -1 if not yet set; >1 means a
1009 * redundant clause */
1010 Selectivity outer_selec; /* selectivity for outer join semantics; -1 if
1013 /* valid if clause is mergejoinable, else NIL */
1014 List *mergeopfamilies; /* opfamilies containing clause operator */
1016 /* cache space for mergeclause processing; NULL if not yet set */
1017 EquivalenceClass *left_ec; /* EquivalenceClass containing lefthand */
1018 EquivalenceClass *right_ec; /* EquivalenceClass containing righthand */
1019 EquivalenceMember *left_em; /* EquivalenceMember for lefthand */
1020 EquivalenceMember *right_em; /* EquivalenceMember for righthand */
1021 List *scansel_cache; /* list of MergeScanSelCache structs */
1023 /* transient workspace for use while considering a specific join path */
1024 bool outer_is_left; /* T = outer var on left, F = on right */
1026 /* valid if clause is hashjoinable, else InvalidOid: */
1027 Oid hashjoinoperator; /* copy of clause operator */
1029 /* cache space for hashclause processing; -1 if not yet set */
1030 Selectivity left_bucketsize; /* avg bucketsize of left side */
1031 Selectivity right_bucketsize; /* avg bucketsize of right side */
1035 * Since mergejoinscansel() is a relatively expensive function, and would
1036 * otherwise be invoked many times while planning a large join tree,
1037 * we go out of our way to cache its results. Each mergejoinable
1038 * RestrictInfo carries a list of the specific sort orderings that have
1039 * been considered for use with it, and the resulting selectivities.
1041 typedef struct MergeScanSelCache
1043 /* Ordering details (cache lookup key) */
1044 Oid opfamily; /* btree opfamily defining the ordering */
1045 int strategy; /* sort direction (ASC or DESC) */
1046 bool nulls_first; /* do NULLs come before normal values? */
1048 Selectivity leftstartsel; /* first-join fraction for clause left side */
1049 Selectivity leftendsel; /* last-join fraction for clause left side */
1050 Selectivity rightstartsel; /* first-join fraction for clause right side */
1051 Selectivity rightendsel; /* last-join fraction for clause right side */
1052 } MergeScanSelCache;
1055 * Inner indexscan info.
1057 * An inner indexscan is one that uses one or more joinclauses as index
1058 * conditions (perhaps in addition to plain restriction clauses). So it
1059 * can only be used as the inner path of a nestloop join where the outer
1060 * relation includes all other relids appearing in those joinclauses.
1061 * The set of usable joinclauses, and thus the best inner indexscan,
1062 * thus varies depending on which outer relation we consider; so we have
1063 * to recompute the best such paths for every join. To avoid lots of
1064 * redundant computation, we cache the results of such searches. For
1065 * each relation we compute the set of possible otherrelids (all relids
1066 * appearing in joinquals that could become indexquals for this table).
1067 * Two outer relations whose relids have the same intersection with this
1068 * set will have the same set of available joinclauses and thus the same
1069 * best inner indexscans for the inner relation. By taking the intersection
1070 * before scanning the cache, we avoid recomputing when considering
1071 * join rels that differ only by the inclusion of irrelevant other rels.
1073 * The search key also includes a bool showing whether the join being
1074 * considered is an outer join. Since we constrain the join order for
1075 * outer joins, I believe that this bool can only have one possible value
1076 * for any particular lookup key; but store it anyway to avoid confusion.
1079 typedef struct InnerIndexscanInfo
1082 /* The lookup key: */
1083 Relids other_relids; /* a set of relevant other relids */
1084 bool isouterjoin; /* true if join is outer */
1085 /* Best paths for this lookup key (NULL if no available indexscans): */
1086 Path *cheapest_startup_innerpath; /* cheapest startup cost */
1087 Path *cheapest_total_innerpath; /* cheapest total cost */
1088 } InnerIndexscanInfo;
1091 * Placeholder node for an expression to be evaluated below the top level
1092 * of a plan tree. This is used during planning to represent the contained
1093 * expression. At the end of the planning process it is replaced by either
1094 * the contained expression or a Var referring to a lower-level evaluation of
1095 * the contained expression. Typically the evaluation occurs below an outer
1096 * join, and Var references above the outer join might thereby yield NULL
1097 * instead of the expression value.
1099 * Although the planner treats this as an expression node type, it is not
1100 * recognized by the parser or executor, so we declare it here rather than
1104 typedef struct PlaceHolderVar
1107 Expr *phexpr; /* the represented expression */
1108 Relids phrels; /* base relids syntactically within expr src */
1109 Index phid; /* ID for PHV (unique within planner run) */
1110 Index phlevelsup; /* > 0 if PHV belongs to outer query */
1114 * "Special join" info.
1116 * One-sided outer joins constrain the order of joining partially but not
1117 * completely. We flatten such joins into the planner's top-level list of
1118 * relations to join, but record information about each outer join in a
1119 * SpecialJoinInfo struct. These structs are kept in the PlannerInfo node's
1122 * Similarly, semijoins and antijoins created by flattening IN (subselect)
1123 * and EXISTS(subselect) clauses create partial constraints on join order.
1124 * These are likewise recorded in SpecialJoinInfo structs.
1126 * We make SpecialJoinInfos for FULL JOINs even though there is no flexibility
1127 * of planning for them, because this simplifies make_join_rel()'s API.
1129 * min_lefthand and min_righthand are the sets of base relids that must be
1130 * available on each side when performing the special join. lhs_strict is
1131 * true if the special join's condition cannot succeed when the LHS variables
1132 * are all NULL (this means that an outer join can commute with upper-level
1133 * outer joins even if it appears in their RHS). We don't bother to set
1134 * lhs_strict for FULL JOINs, however.
1136 * It is not valid for either min_lefthand or min_righthand to be empty sets;
1137 * if they were, this would break the logic that enforces join order.
1139 * syn_lefthand and syn_righthand are the sets of base relids that are
1140 * syntactically below this special join. (These are needed to help compute
1141 * min_lefthand and min_righthand for higher joins.)
1143 * delay_upper_joins is set TRUE if we detect a pushed-down clause that has
1144 * to be evaluated after this join is formed (because it references the RHS).
1145 * Any outer joins that have such a clause and this join in their RHS cannot
1146 * commute with this join, because that would leave noplace to check the
1147 * pushed-down clause. (We don't track this for FULL JOINs, either.)
1149 * join_quals is an implicit-AND list of the quals syntactically associated
1150 * with the join (they may or may not end up being applied at the join level).
1151 * This is just a side list and does not drive actual application of quals.
1152 * For JOIN_SEMI joins, this is cleared to NIL in create_unique_path() if
1153 * the join is found not to be suitable for a uniqueify-the-RHS plan.
1155 * jointype is never JOIN_RIGHT; a RIGHT JOIN is handled by switching
1156 * the inputs to make it a LEFT JOIN. So the allowed values of jointype
1157 * in a join_info_list member are only LEFT, FULL, SEMI, or ANTI.
1159 * For purposes of join selectivity estimation, we create transient
1160 * SpecialJoinInfo structures for regular inner joins; so it is possible
1161 * to have jointype == JOIN_INNER in such a structure, even though this is
1162 * not allowed within join_info_list. We also create transient
1163 * SpecialJoinInfos with jointype == JOIN_INNER for outer joins, since for
1164 * cost estimation purposes it is sometimes useful to know the join size under
1165 * plain innerjoin semantics. Note that lhs_strict, delay_upper_joins, and
1166 * join_quals are not set meaningfully within such structs.
1169 typedef struct SpecialJoinInfo
1172 Relids min_lefthand; /* base relids in minimum LHS for join */
1173 Relids min_righthand; /* base relids in minimum RHS for join */
1174 Relids syn_lefthand; /* base relids syntactically within LHS */
1175 Relids syn_righthand; /* base relids syntactically within RHS */
1176 JoinType jointype; /* always INNER, LEFT, FULL, SEMI, or ANTI */
1177 bool lhs_strict; /* joinclause is strict for some LHS rel */
1178 bool delay_upper_joins; /* can't commute with upper RHS */
1179 List *join_quals; /* join quals, in implicit-AND list format */
1183 * Append-relation info.
1185 * When we expand an inheritable table or a UNION-ALL subselect into an
1186 * "append relation" (essentially, a list of child RTEs), we build an
1187 * AppendRelInfo for each child RTE. The list of AppendRelInfos indicates
1188 * which child RTEs must be included when expanding the parent, and each
1189 * node carries information needed to translate Vars referencing the parent
1190 * into Vars referencing that child.
1192 * These structs are kept in the PlannerInfo node's append_rel_list.
1193 * Note that we just throw all the structs into one list, and scan the
1194 * whole list when desiring to expand any one parent. We could have used
1195 * a more complex data structure (eg, one list per parent), but this would
1196 * be harder to update during operations such as pulling up subqueries,
1197 * and not really any easier to scan. Considering that typical queries
1198 * will not have many different append parents, it doesn't seem worthwhile
1199 * to complicate things.
1201 * Note: after completion of the planner prep phase, any given RTE is an
1202 * append parent having entries in append_rel_list if and only if its
1203 * "inh" flag is set. We clear "inh" for plain tables that turn out not
1204 * to have inheritance children, and (in an abuse of the original meaning
1205 * of the flag) we set "inh" for subquery RTEs that turn out to be
1206 * flattenable UNION ALL queries. This lets us avoid useless searches
1207 * of append_rel_list.
1209 * Note: the data structure assumes that append-rel members are single
1210 * baserels. This is OK for inheritance, but it prevents us from pulling
1211 * up a UNION ALL member subquery if it contains a join. While that could
1212 * be fixed with a more complex data structure, at present there's not much
1213 * point because no improvement in the plan could result.
1216 typedef struct AppendRelInfo
1221 * These fields uniquely identify this append relationship. There can be
1222 * (in fact, always should be) multiple AppendRelInfos for the same
1223 * parent_relid, but never more than one per child_relid, since a given
1224 * RTE cannot be a child of more than one append parent.
1226 Index parent_relid; /* RT index of append parent rel */
1227 Index child_relid; /* RT index of append child rel */
1230 * For an inheritance appendrel, the parent and child are both regular
1231 * relations, and we store their rowtype OIDs here for use in translating
1232 * whole-row Vars. For a UNION-ALL appendrel, the parent and child are
1233 * both subqueries with no named rowtype, and we store InvalidOid here.
1235 Oid parent_reltype; /* OID of parent's composite type */
1236 Oid child_reltype; /* OID of child's composite type */
1239 * The N'th element of this list is a Var or expression representing the
1240 * child column corresponding to the N'th column of the parent. This is
1241 * used to translate Vars referencing the parent rel into references to
1242 * the child. A list element is NULL if it corresponds to a dropped
1243 * column of the parent (this is only possible for inheritance cases, not
1244 * UNION ALL). The list elements are always simple Vars for inheritance
1245 * cases, but can be arbitrary expressions in UNION ALL cases.
1247 * Notice we only store entries for user columns (attno > 0). Whole-row
1248 * Vars are special-cased, and system columns (attno < 0) need no special
1249 * translation since their attnos are the same for all tables.
1251 * Caution: the Vars have varlevelsup = 0. Be careful to adjust as needed
1252 * when copying into a subquery.
1254 List *translated_vars; /* Expressions in the child's Vars */
1257 * We store the parent table's OID here for inheritance, or InvalidOid for
1258 * UNION ALL. This is only needed to help in generating error messages if
1259 * an attempt is made to reference a dropped parent column.
1261 Oid parent_reloid; /* OID of parent relation */
1265 * For each distinct placeholder expression generated during planning, we
1266 * store a PlaceHolderInfo node in the PlannerInfo node's placeholder_list.
1267 * This stores info that is needed centrally rather than in each copy of the
1268 * PlaceHolderVar. The phid fields identify which PlaceHolderInfo goes with
1269 * each PlaceHolderVar. Note that phid is unique throughout a planner run,
1270 * not just within a query level --- this is so that we need not reassign ID's
1271 * when pulling a subquery into its parent.
1273 * The idea is to evaluate the expression at (only) the ph_eval_at join level,
1274 * then allow it to bubble up like a Var until the ph_needed join level.
1275 * ph_needed has the same definition as attr_needed for a regular Var.
1277 * We create a PlaceHolderInfo only after determining that the PlaceHolderVar
1278 * is actually referenced in the plan tree.
1281 typedef struct PlaceHolderInfo
1285 Index phid; /* ID for PH (unique within planner run) */
1286 PlaceHolderVar *ph_var; /* copy of PlaceHolderVar tree */
1287 Relids ph_eval_at; /* lowest level we can evaluate value at */
1288 Relids ph_needed; /* highest level the value is needed at */
1289 int32 ph_width; /* estimated attribute width */
1293 * glob->paramlist keeps track of the PARAM_EXEC slots that we have decided
1294 * we need for the query. At runtime these slots are used to pass values
1295 * either down into subqueries (for outer references in subqueries) or up out
1296 * of subqueries (for the results of a subplan). The n'th entry in the list
1297 * (n counts from 0) corresponds to Param->paramid = n.
1299 * Each paramlist item shows the absolute query level it is associated with,
1300 * where the outermost query is level 1 and nested subqueries have higher
1301 * numbers. The item the parameter slot represents can be one of three kinds:
1303 * A Var: the slot represents a variable of that level that must be passed
1304 * down because subqueries have outer references to it. The varlevelsup
1305 * value in the Var will always be zero.
1307 * An Aggref (with an expression tree representing its argument): the slot
1308 * represents an aggregate expression that is an outer reference for some
1309 * subquery. The Aggref itself has agglevelsup = 0, and its argument tree
1310 * is adjusted to match in level.
1312 * A Param: the slot holds the result of a subplan (it is a setParam item
1313 * for that subplan). The absolute level shown for such items corresponds
1314 * to the parent query of the subplan.
1316 * Note: we detect duplicate Var parameters and coalesce them into one slot,
1317 * but we do not do this for Aggref or Param slots.
1319 typedef struct PlannerParamItem
1323 Node *item; /* the Var, Aggref, or Param */
1324 Index abslevel; /* its absolute query level */
1327 #endif /* RELATION_H */