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 1.175 2009/09/17 20:49:29 tgl 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 */
196 /* optional private data for join_search_hook, e.g., GEQO */
197 void *join_search_private;
202 * In places where it's known that simple_rte_array[] must have been prepared
203 * already, we just index into it to fetch RTEs. In code that might be
204 * executed before or after entering query_planner(), use this macro.
206 #define planner_rt_fetch(rti, root) \
207 ((root)->simple_rte_array ? (root)->simple_rte_array[rti] : \
208 rt_fetch(rti, (root)->parse->rtable))
213 * Per-relation information for planning/optimization
215 * For planning purposes, a "base rel" is either a plain relation (a table)
216 * or the output of a sub-SELECT or function that appears in the range table.
217 * In either case it is uniquely identified by an RT index. A "joinrel"
218 * is the joining of two or more base rels. A joinrel is identified by
219 * the set of RT indexes for its component baserels. We create RelOptInfo
220 * nodes for each baserel and joinrel, and store them in the PlannerInfo's
221 * simple_rel_array and join_rel_list respectively.
223 * Note that there is only one joinrel for any given set of component
224 * baserels, no matter what order we assemble them in; so an unordered
225 * set is the right datatype to identify it with.
227 * We also have "other rels", which are like base rels in that they refer to
228 * single RT indexes; but they are not part of the join tree, and are given
229 * a different RelOptKind to identify them.
231 * Currently the only kind of otherrels are those made for member relations
232 * of an "append relation", that is an inheritance set or UNION ALL subquery.
233 * An append relation has a parent RTE that is a base rel, which represents
234 * the entire append relation. The member RTEs are otherrels. The parent
235 * is present in the query join tree but the members are not. The member
236 * RTEs and otherrels are used to plan the scans of the individual tables or
237 * subqueries of the append set; then the parent baserel is given an Append
238 * plan comprising the best plans for the individual member rels. (See
239 * comments for AppendRelInfo for more information.)
241 * At one time we also made otherrels to represent join RTEs, for use in
242 * handling join alias Vars. Currently this is not needed because all join
243 * alias Vars are expanded to non-aliased form during preprocess_expression.
245 * Parts of this data structure are specific to various scan and join
246 * mechanisms. It didn't seem worth creating new node types for them.
248 * relids - Set of base-relation identifiers; it is a base relation
249 * if there is just one, a join relation if more than one
250 * rows - estimated number of tuples in the relation after restriction
251 * clauses have been applied (ie, output rows of a plan for it)
252 * width - avg. number of bytes per tuple in the relation after the
253 * appropriate projections have been done (ie, output width)
254 * reltargetlist - List of Var and PlaceHolderVar nodes for the values
255 * we need to output from this relation.
256 * List is in no particular order, but all rels of an
257 * appendrel set must use corresponding orders.
258 * NOTE: in a child relation, may contain RowExpr or
259 * ConvertRowtypeExpr representing a whole-row Var.
260 * pathlist - List of Path nodes, one for each potentially useful
261 * method of generating the relation
262 * cheapest_startup_path - the pathlist member with lowest startup cost
263 * (regardless of its ordering)
264 * cheapest_total_path - the pathlist member with lowest total cost
265 * (regardless of its ordering)
266 * cheapest_unique_path - for caching cheapest path to produce unique
267 * (no duplicates) output from relation
269 * If the relation is a base relation it will have these fields set:
271 * relid - RTE index (this is redundant with the relids field, but
272 * is provided for convenience of access)
273 * rtekind - distinguishes plain relation, subquery, or function RTE
274 * min_attr, max_attr - range of valid AttrNumbers for rel
275 * attr_needed - array of bitmapsets indicating the highest joinrel
276 * in which each attribute is needed; if bit 0 is set then
277 * the attribute is needed as part of final targetlist
278 * attr_widths - cache space for per-attribute width estimates;
279 * zero means not computed yet
280 * indexlist - list of IndexOptInfo nodes for relation's indexes
281 * (always NIL if it's not a table)
282 * pages - number of disk pages in relation (zero if not a table)
283 * tuples - number of tuples in relation (not considering restrictions)
284 * subplan - plan for subquery (NULL if it's not a subquery)
285 * subrtable - rangetable for subquery (NIL if it's not a subquery)
287 * Note: for a subquery, tuples and subplan are not set immediately
288 * upon creation of the RelOptInfo object; they are filled in when
289 * set_base_rel_pathlist processes the object.
291 * For otherrels that are appendrel members, these fields are filled
292 * in just as for a baserel.
294 * The presence of the remaining fields depends on the restrictions
295 * and joins that the relation participates in:
297 * baserestrictinfo - List of RestrictInfo nodes, containing info about
298 * each non-join qualification clause in which this relation
299 * participates (only used for base rels)
300 * baserestrictcost - Estimated cost of evaluating the baserestrictinfo
301 * clauses at a single tuple (only used for base rels)
302 * joininfo - List of RestrictInfo nodes, containing info about each
303 * join clause in which this relation participates (but
304 * note this excludes clauses that might be derivable from
305 * EquivalenceClasses)
306 * has_eclass_joins - flag that EquivalenceClass joins are possible
307 * index_outer_relids - only used for base rels; set of outer relids
308 * that participate in indexable joinclauses for this rel
309 * index_inner_paths - only used for base rels; list of InnerIndexscanInfo
310 * nodes showing best indexpaths for various subsets of
311 * index_outer_relids.
313 * Note: Keeping a restrictinfo list in the RelOptInfo is useful only for
314 * base rels, because for a join rel the set of clauses that are treated as
315 * restrict clauses varies depending on which sub-relations we choose to join.
316 * (For example, in a 3-base-rel join, a clause relating rels 1 and 2 must be
317 * treated as a restrictclause if we join {1} and {2 3} to make {1 2 3}; but
318 * if we join {1 2} and {3} then that clause will be a restrictclause in {1 2}
319 * and should not be processed again at the level of {1 2 3}.) Therefore,
320 * the restrictinfo list in the join case appears in individual JoinPaths
321 * (field joinrestrictinfo), not in the parent relation. But it's OK for
322 * the RelOptInfo to store the joininfo list, because that is the same
323 * for a given rel no matter how we form it.
325 * We store baserestrictcost in the RelOptInfo (for base relations) because
326 * we know we will need it at least once (to price the sequential scan)
327 * and may need it multiple times to price index scans.
330 typedef enum RelOptKind
334 RELOPT_OTHER_MEMBER_REL
337 typedef struct RelOptInfo
341 RelOptKind reloptkind;
343 /* all relations included in this RelOptInfo */
344 Relids relids; /* set of base relids (rangetable indexes) */
346 /* size estimates generated by planner */
347 double rows; /* estimated number of result tuples */
348 int width; /* estimated avg width of result tuples */
350 /* materialization information */
351 List *reltargetlist; /* Vars to be output by scan of relation */
352 List *pathlist; /* Path structures */
353 struct Path *cheapest_startup_path;
354 struct Path *cheapest_total_path;
355 struct Path *cheapest_unique_path;
357 /* information about a base rel (not set for join rels!) */
359 RTEKind rtekind; /* RELATION, SUBQUERY, or FUNCTION */
360 AttrNumber min_attr; /* smallest attrno of rel (often <0) */
361 AttrNumber max_attr; /* largest attrno of rel */
362 Relids *attr_needed; /* array indexed [min_attr .. max_attr] */
363 int32 *attr_widths; /* array indexed [min_attr .. max_attr] */
364 List *indexlist; /* list of IndexOptInfo */
367 struct Plan *subplan; /* if subquery */
368 List *subrtable; /* if subquery */
370 /* used by various scans and joins: */
371 List *baserestrictinfo; /* RestrictInfo structures (if base
373 QualCost baserestrictcost; /* cost of evaluating the above */
374 List *joininfo; /* RestrictInfo structures for join clauses
375 * involving this rel */
376 bool has_eclass_joins; /* T means joininfo is incomplete */
378 /* cached info about inner indexscan paths for relation: */
379 Relids index_outer_relids; /* other relids in indexable join
381 List *index_inner_paths; /* InnerIndexscanInfo nodes */
384 * Inner indexscans are not in the main pathlist because they are not
385 * usable except in specific join contexts. We use the index_inner_paths
386 * list just to avoid recomputing the best inner indexscan repeatedly for
387 * similar outer relations. See comments for InnerIndexscanInfo.
393 * Per-index information for planning/optimization
395 * Prior to Postgres 7.0, RelOptInfo was used to describe both relations
396 * and indexes, but that created confusion without actually doing anything
397 * useful. So now we have a separate IndexOptInfo struct for indexes.
399 * opfamily[], indexkeys[], opcintype[], fwdsortop[], revsortop[],
400 * and nulls_first[] each have ncolumns entries.
401 * Note: for historical reasons, the opfamily array has an extra entry
402 * that is always zero. Some code scans until it sees a zero entry,
403 * rather than looking at ncolumns.
405 * Zeroes in the indexkeys[] array indicate index columns that are
406 * expressions; there is one element in indexprs for each such column.
408 * For an unordered index, the sortop arrays contains zeroes. Note that
409 * fwdsortop[] and nulls_first[] describe the sort ordering of a forward
410 * indexscan; we can also consider a backward indexscan, which will
411 * generate sort order described by revsortop/!nulls_first.
413 * The indexprs and indpred expressions have been run through
414 * prepqual.c and eval_const_expressions() for ease of matching to
415 * WHERE clauses. indpred is in implicit-AND form.
417 typedef struct IndexOptInfo
421 Oid indexoid; /* OID of the index relation */
422 RelOptInfo *rel; /* back-link to index's table */
424 /* statistics from pg_class */
425 BlockNumber pages; /* number of disk pages in index */
426 double tuples; /* number of index tuples in index */
428 /* index descriptor information */
429 int ncolumns; /* number of columns in index */
430 Oid *opfamily; /* OIDs of operator families for columns */
431 int *indexkeys; /* column numbers of index's keys, or 0 */
432 Oid *opcintype; /* OIDs of opclass declared input data types */
433 Oid *fwdsortop; /* OIDs of sort operators for each column */
434 Oid *revsortop; /* OIDs of sort operators for backward scan */
435 bool *nulls_first; /* do NULLs come first in the sort order? */
436 Oid relam; /* OID of the access method (in pg_am) */
438 RegProcedure amcostestimate; /* OID of the access method's cost fcn */
440 List *indexprs; /* expressions for non-simple index columns */
441 List *indpred; /* predicate if a partial index, else NIL */
443 bool predOK; /* true if predicate matches query */
444 bool unique; /* true if a unique index */
445 bool amoptionalkey; /* can query omit key for the first column? */
446 bool amsearchnulls; /* can AM search for NULL index entries? */
447 bool amhasgettuple; /* does AM have amgettuple interface? */
448 bool amhasgetbitmap; /* does AM have amgetbitmap interface? */
455 * Whenever we can determine that a mergejoinable equality clause A = B is
456 * not delayed by any outer join, we create an EquivalenceClass containing
457 * the expressions A and B to record this knowledge. If we later find another
458 * equivalence B = C, we add C to the existing EquivalenceClass; this may
459 * require merging two existing EquivalenceClasses. At the end of the qual
460 * distribution process, we have sets of values that are known all transitively
461 * equal to each other, where "equal" is according to the rules of the btree
462 * operator family(s) shown in ec_opfamilies. (We restrict an EC to contain
463 * only equalities whose operators belong to the same set of opfamilies. This
464 * could probably be relaxed, but for now it's not worth the trouble, since
465 * nearly all equality operators belong to only one btree opclass anyway.)
467 * We also use EquivalenceClasses as the base structure for PathKeys, letting
468 * us represent knowledge about different sort orderings being equivalent.
469 * Since every PathKey must reference an EquivalenceClass, we will end up
470 * with single-member EquivalenceClasses whenever a sort key expression has
471 * not been equivalenced to anything else. It is also possible that such an
472 * EquivalenceClass will contain a volatile expression ("ORDER BY random()"),
473 * which is a case that can't arise otherwise since clauses containing
474 * volatile functions are never considered mergejoinable. We mark such
475 * EquivalenceClasses specially to prevent them from being merged with
476 * ordinary EquivalenceClasses. Also, for volatile expressions we have
477 * to be careful to match the EquivalenceClass to the correct targetlist
478 * entry: consider SELECT random() AS a, random() AS b ... ORDER BY b,a.
479 * So we record the SortGroupRef of the originating sort clause.
481 * We allow equality clauses appearing below the nullable side of an outer join
482 * to form EquivalenceClasses, but these have a slightly different meaning:
483 * the included values might be all NULL rather than all the same non-null
484 * values. See src/backend/optimizer/README for more on that point.
486 * NB: if ec_merged isn't NULL, this class has been merged into another, and
487 * should be ignored in favor of using the pointed-to class.
489 typedef struct EquivalenceClass
493 List *ec_opfamilies; /* btree operator family OIDs */
494 List *ec_members; /* list of EquivalenceMembers */
495 List *ec_sources; /* list of generating RestrictInfos */
496 List *ec_derives; /* list of derived RestrictInfos */
497 Relids ec_relids; /* all relids appearing in ec_members */
498 bool ec_has_const; /* any pseudoconstants in ec_members? */
499 bool ec_has_volatile; /* the (sole) member is a volatile expr */
500 bool ec_below_outer_join; /* equivalence applies below an OJ */
501 bool ec_broken; /* failed to generate needed clauses? */
502 Index ec_sortref; /* originating sortclause label, or 0 */
503 struct EquivalenceClass *ec_merged; /* set if merged into another EC */
507 * If an EC contains a const and isn't below-outer-join, any PathKey depending
508 * on it must be redundant, since there's only one possible value of the key.
510 #define EC_MUST_BE_REDUNDANT(eclass) \
511 ((eclass)->ec_has_const && !(eclass)->ec_below_outer_join)
514 * EquivalenceMember - one member expression of an EquivalenceClass
516 * em_is_child signifies that this element was built by transposing a member
517 * for an inheritance parent relation to represent the corresponding expression
518 * on an inheritance child. The element should be ignored for all purposes
519 * except constructing inner-indexscan paths for the child relation. (Other
520 * types of join are driven from transposed joininfo-list entries.) Note
521 * that the EC's ec_relids field does NOT include the child relation.
523 * em_datatype is usually the same as exprType(em_expr), but can be
524 * different when dealing with a binary-compatible opfamily; in particular
525 * anyarray_ops would never work without this. Use em_datatype when
526 * looking up a specific btree operator to work with this expression.
528 typedef struct EquivalenceMember
532 Expr *em_expr; /* the expression represented */
533 Relids em_relids; /* all relids appearing in em_expr */
534 bool em_is_const; /* expression is pseudoconstant? */
535 bool em_is_child; /* derived version for a child relation? */
536 Oid em_datatype; /* the "nominal type" used by the opfamily */
542 * The sort ordering of a path is represented by a list of PathKey nodes.
543 * An empty list implies no known ordering. Otherwise the first item
544 * represents the primary sort key, the second the first secondary sort key,
545 * etc. The value being sorted is represented by linking to an
546 * EquivalenceClass containing that value and including pk_opfamily among its
547 * ec_opfamilies. This is a convenient method because it makes it trivial
548 * to detect equivalent and closely-related orderings. (See optimizer/README
549 * for more information.)
551 * Note: pk_strategy is either BTLessStrategyNumber (for ASC) or
552 * BTGreaterStrategyNumber (for DESC). We assume that all ordering-capable
553 * index types will use btree-compatible strategy numbers.
556 typedef struct PathKey
560 EquivalenceClass *pk_eclass; /* the value that is ordered */
561 Oid pk_opfamily; /* btree opfamily defining the ordering */
562 int pk_strategy; /* sort direction (ASC or DESC) */
563 bool pk_nulls_first; /* do NULLs come before normal values? */
567 * Type "Path" is used as-is for sequential-scan paths, as well as some other
568 * simple plan types that we don't need any extra information in the path for.
569 * For other path types it is the first component of a larger struct.
571 * Note: "pathtype" is the NodeTag of the Plan node we could build from this
572 * Path. It is partially redundant with the Path's NodeTag, but allows us
573 * to use the same Path type for multiple Plan types where there is no need
574 * to distinguish the Plan type during path processing.
581 NodeTag pathtype; /* tag identifying scan/join method */
583 RelOptInfo *parent; /* the relation this path can build */
585 /* estimated execution costs for path (see costsize.c for more info) */
586 Cost startup_cost; /* cost expended before fetching any tuples */
587 Cost total_cost; /* total cost (assuming all tuples fetched) */
589 List *pathkeys; /* sort ordering of path's output */
590 /* pathkeys is a List of PathKey nodes; see above */
594 * IndexPath represents an index scan over a single index.
596 * 'indexinfo' is the index to be scanned.
598 * 'indexclauses' is a list of index qualification clauses, with implicit
599 * AND semantics across the list. Each clause is a RestrictInfo node from
600 * the query's WHERE or JOIN conditions.
602 * 'indexquals' has the same structure as 'indexclauses', but it contains
603 * the actual indexqual conditions that can be used with the index.
604 * In simple cases this is identical to 'indexclauses', but when special
605 * indexable operators appear in 'indexclauses', they are replaced by the
606 * derived indexscannable conditions in 'indexquals'.
608 * 'isjoininner' is TRUE if the path is a nestloop inner scan (that is,
609 * some of the index conditions are join rather than restriction clauses).
610 * Note that the path costs will be calculated differently from a plain
611 * indexscan in this case, and in addition there's a special 'rows' value
612 * different from the parent RelOptInfo's (see below).
614 * 'indexscandir' is one of:
615 * ForwardScanDirection: forward scan of an ordered index
616 * BackwardScanDirection: backward scan of an ordered index
617 * NoMovementScanDirection: scan of an unordered index, or don't care
618 * (The executor doesn't care whether it gets ForwardScanDirection or
619 * NoMovementScanDirection for an indexscan, but the planner wants to
620 * distinguish ordered from unordered indexes for building pathkeys.)
622 * 'indextotalcost' and 'indexselectivity' are saved in the IndexPath so that
623 * we need not recompute them when considering using the same index in a
624 * bitmap index/heap scan (see BitmapHeapPath). The costs of the IndexPath
625 * itself represent the costs of an IndexScan plan type.
627 * 'rows' is the estimated result tuple count for the indexscan. This
628 * is the same as path.parent->rows for a simple indexscan, but it is
629 * different for a nestloop inner scan, because the additional indexquals
630 * coming from join clauses make the scan more selective than the parent
631 * rel's restrict clauses alone would do.
634 typedef struct IndexPath
637 IndexOptInfo *indexinfo;
641 ScanDirection indexscandir;
643 Selectivity indexselectivity;
644 double rows; /* estimated number of result tuples */
648 * BitmapHeapPath represents one or more indexscans that generate TID bitmaps
649 * instead of directly accessing the heap, followed by AND/OR combinations
650 * to produce a single bitmap, followed by a heap scan that uses the bitmap.
651 * Note that the output is always considered unordered, since it will come
652 * out in physical heap order no matter what the underlying indexes did.
654 * The individual indexscans are represented by IndexPath nodes, and any
655 * logic on top of them is represented by a tree of BitmapAndPath and
656 * BitmapOrPath nodes. Notice that we can use the same IndexPath node both
657 * to represent a regular IndexScan plan, and as the child of a BitmapHeapPath
658 * that represents scanning the same index using a BitmapIndexScan. The
659 * startup_cost and total_cost figures of an IndexPath always represent the
660 * costs to use it as a regular IndexScan. The costs of a BitmapIndexScan
661 * can be computed using the IndexPath's indextotalcost and indexselectivity.
663 * BitmapHeapPaths can be nestloop inner indexscans. The isjoininner and
664 * rows fields serve the same purpose as for plain IndexPaths.
666 typedef struct BitmapHeapPath
669 Path *bitmapqual; /* IndexPath, BitmapAndPath, BitmapOrPath */
670 bool isjoininner; /* T if it's a nestloop inner scan */
671 double rows; /* estimated number of result tuples */
675 * BitmapAndPath represents a BitmapAnd plan node; it can only appear as
676 * part of the substructure of a BitmapHeapPath. The Path structure is
677 * a bit more heavyweight than we really need for this, but for simplicity
678 * we make it a derivative of Path anyway.
680 typedef struct BitmapAndPath
683 List *bitmapquals; /* IndexPaths and BitmapOrPaths */
684 Selectivity bitmapselectivity;
688 * BitmapOrPath represents a BitmapOr plan node; it can only appear as
689 * part of the substructure of a BitmapHeapPath. The Path structure is
690 * a bit more heavyweight than we really need for this, but for simplicity
691 * we make it a derivative of Path anyway.
693 typedef struct BitmapOrPath
696 List *bitmapquals; /* IndexPaths and BitmapAndPaths */
697 Selectivity bitmapselectivity;
701 * TidPath represents a scan by TID
703 * tidquals is an implicitly OR'ed list of qual expressions of the form
704 * "CTID = pseudoconstant" or "CTID = ANY(pseudoconstant_array)".
705 * Note they are bare expressions, not RestrictInfos.
707 typedef struct TidPath
710 List *tidquals; /* qual(s) involving CTID = something */
714 * AppendPath represents an Append plan, ie, successive execution of
715 * several member plans.
717 * Note: it is possible for "subpaths" to contain only one, or even no,
718 * elements. These cases are optimized during create_append_plan.
719 * In particular, an AppendPath with no subpaths is a "dummy" path that
720 * is created to represent the case that a relation is provably empty.
722 typedef struct AppendPath
725 List *subpaths; /* list of component Paths */
728 #define IS_DUMMY_PATH(p) \
729 (IsA((p), AppendPath) && ((AppendPath *) (p))->subpaths == NIL)
732 * ResultPath represents use of a Result plan node to compute a variable-free
733 * targetlist with no underlying tables (a "SELECT expressions" query).
734 * The query could have a WHERE clause, too, represented by "quals".
736 * Note that quals is a list of bare clauses, not RestrictInfos.
738 typedef struct ResultPath
745 * MaterialPath represents use of a Material plan node, i.e., caching of
746 * the output of its subpath. This is used when the subpath is expensive
747 * and needs to be scanned repeatedly, or when we need mark/restore ability
748 * and the subpath doesn't have it.
750 typedef struct MaterialPath
757 * UniquePath represents elimination of distinct rows from the output of
760 * This is unlike the other Path nodes in that it can actually generate
761 * different plans: either hash-based or sort-based implementation, or a
762 * no-op if the input path can be proven distinct already. The decision
763 * is sufficiently localized that it's not worth having separate Path node
764 * types. (Note: in the no-op case, we could eliminate the UniquePath node
765 * entirely and just return the subpath; but it's convenient to have a
766 * UniquePath in the path tree to signal upper-level routines that the input
767 * is known distinct.)
771 UNIQUE_PATH_NOOP, /* input is known unique already */
772 UNIQUE_PATH_HASH, /* use hashing */
773 UNIQUE_PATH_SORT /* use sorting */
776 typedef struct UniquePath
780 UniquePathMethod umethod;
781 List *in_operators; /* equality operators of the IN clause */
782 List *uniq_exprs; /* expressions to be made unique */
783 double rows; /* estimated number of result tuples */
787 * NoOpPath represents exactly the same plan as its subpath. This is used
788 * when we have determined that a join can be eliminated. The difference
789 * between the NoOpPath and its subpath is just that the NoOpPath's parent
790 * is the whole join relation while the subpath is for one of the joined
791 * relations (and the other one isn't needed).
793 * Note: path.pathtype is always T_Join, but this won't actually give rise
794 * to a Join plan node.
796 typedef struct NoOpPath
803 * All join-type paths share these fields.
806 typedef struct JoinPath
812 Path *outerjoinpath; /* path for the outer side of the join */
813 Path *innerjoinpath; /* path for the inner side of the join */
815 List *joinrestrictinfo; /* RestrictInfos to apply to join */
818 * See the notes for RelOptInfo to understand why joinrestrictinfo is
819 * needed in JoinPath, and can't be merged into the parent RelOptInfo.
824 * A nested-loop path needs no special fields.
827 typedef JoinPath NestPath;
830 * A mergejoin path has these fields.
832 * path_mergeclauses lists the clauses (in the form of RestrictInfos)
833 * that will be used in the merge.
835 * Note that the mergeclauses are a subset of the parent relation's
836 * restriction-clause list. Any join clauses that are not mergejoinable
837 * appear only in the parent's restrict list, and must be checked by a
838 * qpqual at execution time.
840 * outersortkeys (resp. innersortkeys) is NIL if the outer path
841 * (resp. inner path) is already ordered appropriately for the
842 * mergejoin. If it is not NIL then it is a PathKeys list describing
843 * the ordering that must be created by an explicit sort step.
846 typedef struct MergePath
849 List *path_mergeclauses; /* join clauses to be used for merge */
850 List *outersortkeys; /* keys for explicit sort, if any */
851 List *innersortkeys; /* keys for explicit sort, if any */
855 * A hashjoin path has these fields.
857 * The remarks above for mergeclauses apply for hashclauses as well.
859 * Hashjoin does not care what order its inputs appear in, so we have
860 * no need for sortkeys.
863 typedef struct HashPath
866 List *path_hashclauses; /* join clauses used for hashing */
867 int num_batches; /* number of batches expected */
871 * Restriction clause info.
873 * We create one of these for each AND sub-clause of a restriction condition
874 * (WHERE or JOIN/ON clause). Since the restriction clauses are logically
875 * ANDed, we can use any one of them or any subset of them to filter out
876 * tuples, without having to evaluate the rest. The RestrictInfo node itself
877 * stores data used by the optimizer while choosing the best query plan.
879 * If a restriction clause references a single base relation, it will appear
880 * in the baserestrictinfo list of the RelOptInfo for that base rel.
882 * If a restriction clause references more than one base rel, it will
883 * appear in the joininfo list of every RelOptInfo that describes a strict
884 * subset of the base rels mentioned in the clause. The joininfo lists are
885 * used to drive join tree building by selecting plausible join candidates.
886 * The clause cannot actually be applied until we have built a join rel
887 * containing all the base rels it references, however.
889 * When we construct a join rel that includes all the base rels referenced
890 * in a multi-relation restriction clause, we place that clause into the
891 * joinrestrictinfo lists of paths for the join rel, if neither left nor
892 * right sub-path includes all base rels referenced in the clause. The clause
893 * will be applied at that join level, and will not propagate any further up
894 * the join tree. (Note: the "predicate migration" code was once intended to
895 * push restriction clauses up and down the plan tree based on evaluation
896 * costs, but it's dead code and is unlikely to be resurrected in the
897 * foreseeable future.)
899 * Note that in the presence of more than two rels, a multi-rel restriction
900 * might reach different heights in the join tree depending on the join
901 * sequence we use. So, these clauses cannot be associated directly with
902 * the join RelOptInfo, but must be kept track of on a per-join-path basis.
904 * RestrictInfos that represent equivalence conditions (i.e., mergejoinable
905 * equalities that are not outerjoin-delayed) are handled a bit differently.
906 * Initially we attach them to the EquivalenceClasses that are derived from
907 * them. When we construct a scan or join path, we look through all the
908 * EquivalenceClasses and generate derived RestrictInfos representing the
909 * minimal set of conditions that need to be checked for this particular scan
910 * or join to enforce that all members of each EquivalenceClass are in fact
911 * equal in all rows emitted by the scan or join.
913 * When dealing with outer joins we have to be very careful about pushing qual
914 * clauses up and down the tree. An outer join's own JOIN/ON conditions must
915 * be evaluated exactly at that join node, unless they are "degenerate"
916 * conditions that reference only Vars from the nullable side of the join.
917 * Quals appearing in WHERE or in a JOIN above the outer join cannot be pushed
918 * down below the outer join, if they reference any nullable Vars.
919 * RestrictInfo nodes contain a flag to indicate whether a qual has been
920 * pushed down to a lower level than its original syntactic placement in the
921 * join tree would suggest. If an outer join prevents us from pushing a qual
922 * down to its "natural" semantic level (the level associated with just the
923 * base rels used in the qual) then we mark the qual with a "required_relids"
924 * value including more than just the base rels it actually uses. By
925 * pretending that the qual references all the rels required to form the outer
926 * join, we prevent it from being evaluated below the outer join's joinrel.
927 * When we do form the outer join's joinrel, we still need to distinguish
928 * those quals that are actually in that join's JOIN/ON condition from those
929 * that appeared elsewhere in the tree and were pushed down to the join rel
930 * because they used no other rels. That's what the is_pushed_down flag is
931 * for; it tells us that a qual is not an OUTER JOIN qual for the set of base
932 * rels listed in required_relids. A clause that originally came from WHERE
933 * or an INNER JOIN condition will *always* have its is_pushed_down flag set.
934 * It's possible for an OUTER JOIN clause to be marked is_pushed_down too,
935 * if we decide that it can be pushed down into the nullable side of the join.
936 * In that case it acts as a plain filter qual for wherever it gets evaluated.
937 * (In short, is_pushed_down is only false for non-degenerate outer join
938 * conditions. Possibly we should rename it to reflect that meaning?)
940 * RestrictInfo nodes also contain an outerjoin_delayed flag, which is true
941 * if the clause's applicability must be delayed due to any outer joins
942 * appearing below it (ie, it has to be postponed to some join level higher
943 * than the set of relations it actually references). There is also a
944 * nullable_relids field, which is the set of rels it references that can be
945 * forced null by some outer join below the clause. outerjoin_delayed = true
946 * is subtly different from nullable_relids != NULL: a clause might reference
947 * some nullable rels and yet not be outerjoin_delayed because it also
948 * references all the other rels of the outer join(s). A clause that is not
949 * outerjoin_delayed can be enforced anywhere it is computable.
951 * In general, the referenced clause might be arbitrarily complex. The
952 * kinds of clauses we can handle as indexscan quals, mergejoin clauses,
953 * or hashjoin clauses are limited (e.g., no volatile functions). The code
954 * for each kind of path is responsible for identifying the restrict clauses
955 * it can use and ignoring the rest. Clauses not implemented by an indexscan,
956 * mergejoin, or hashjoin will be placed in the plan qual or joinqual field
957 * of the finished Plan node, where they will be enforced by general-purpose
958 * qual-expression-evaluation code. (But we are still entitled to count
959 * their selectivity when estimating the result tuple count, if we
960 * can guess what it is...)
962 * When the referenced clause is an OR clause, we generate a modified copy
963 * in which additional RestrictInfo nodes are inserted below the top-level
964 * OR/AND structure. This is a convenience for OR indexscan processing:
965 * indexquals taken from either the top level or an OR subclause will have
966 * associated RestrictInfo nodes.
968 * The can_join flag is set true if the clause looks potentially useful as
969 * a merge or hash join clause, that is if it is a binary opclause with
970 * nonoverlapping sets of relids referenced in the left and right sides.
971 * (Whether the operator is actually merge or hash joinable isn't checked,
974 * The pseudoconstant flag is set true if the clause contains no Vars of
975 * the current query level and no volatile functions. Such a clause can be
976 * pulled out and used as a one-time qual in a gating Result node. We keep
977 * pseudoconstant clauses in the same lists as other RestrictInfos so that
978 * the regular clause-pushing machinery can assign them to the correct join
979 * level, but they need to be treated specially for cost and selectivity
980 * estimates. Note that a pseudoconstant clause can never be an indexqual
981 * or merge or hash join clause, so it's of no interest to large parts of
984 * When join clauses are generated from EquivalenceClasses, there may be
985 * several equally valid ways to enforce join equivalence, of which we need
986 * apply only one. We mark clauses of this kind by setting parent_ec to
987 * point to the generating EquivalenceClass. Multiple clauses with the same
988 * parent_ec in the same join are redundant.
991 typedef struct RestrictInfo
995 Expr *clause; /* the represented clause of WHERE or JOIN */
997 bool is_pushed_down; /* TRUE if clause was pushed down in level */
999 bool outerjoin_delayed; /* TRUE if delayed by lower outer join */
1001 bool can_join; /* see comment above */
1003 bool pseudoconstant; /* see comment above */
1005 /* The set of relids (varnos) actually referenced in the clause: */
1006 Relids clause_relids;
1008 /* The set of relids required to evaluate the clause: */
1009 Relids required_relids;
1011 /* The relids used in the clause that are nullable by lower outer joins: */
1012 Relids nullable_relids;
1014 /* These fields are set for any binary opclause: */
1015 Relids left_relids; /* relids in left side of clause */
1016 Relids right_relids; /* relids in right side of clause */
1018 /* This field is NULL unless clause is an OR clause: */
1019 Expr *orclause; /* modified clause with RestrictInfos */
1021 /* This field is NULL unless clause is potentially redundant: */
1022 EquivalenceClass *parent_ec; /* generating EquivalenceClass */
1024 /* cache space for cost and selectivity */
1025 QualCost eval_cost; /* eval cost of clause; -1 if not yet set */
1026 Selectivity norm_selec; /* selectivity for "normal" (JOIN_INNER)
1027 * semantics; -1 if not yet set; >1 means a
1028 * redundant clause */
1029 Selectivity outer_selec; /* selectivity for outer join semantics; -1 if
1032 /* valid if clause is mergejoinable, else NIL */
1033 List *mergeopfamilies; /* opfamilies containing clause operator */
1035 /* cache space for mergeclause processing; NULL if not yet set */
1036 EquivalenceClass *left_ec; /* EquivalenceClass containing lefthand */
1037 EquivalenceClass *right_ec; /* EquivalenceClass containing righthand */
1038 EquivalenceMember *left_em; /* EquivalenceMember for lefthand */
1039 EquivalenceMember *right_em; /* EquivalenceMember for righthand */
1040 List *scansel_cache; /* list of MergeScanSelCache structs */
1042 /* transient workspace for use while considering a specific join path */
1043 bool outer_is_left; /* T = outer var on left, F = on right */
1045 /* valid if clause is hashjoinable, else InvalidOid: */
1046 Oid hashjoinoperator; /* copy of clause operator */
1048 /* cache space for hashclause processing; -1 if not yet set */
1049 Selectivity left_bucketsize; /* avg bucketsize of left side */
1050 Selectivity right_bucketsize; /* avg bucketsize of right side */
1054 * Since mergejoinscansel() is a relatively expensive function, and would
1055 * otherwise be invoked many times while planning a large join tree,
1056 * we go out of our way to cache its results. Each mergejoinable
1057 * RestrictInfo carries a list of the specific sort orderings that have
1058 * been considered for use with it, and the resulting selectivities.
1060 typedef struct MergeScanSelCache
1062 /* Ordering details (cache lookup key) */
1063 Oid opfamily; /* btree opfamily defining the ordering */
1064 int strategy; /* sort direction (ASC or DESC) */
1065 bool nulls_first; /* do NULLs come before normal values? */
1067 Selectivity leftstartsel; /* first-join fraction for clause left side */
1068 Selectivity leftendsel; /* last-join fraction for clause left side */
1069 Selectivity rightstartsel; /* first-join fraction for clause right side */
1070 Selectivity rightendsel; /* last-join fraction for clause right side */
1071 } MergeScanSelCache;
1074 * Inner indexscan info.
1076 * An inner indexscan is one that uses one or more joinclauses as index
1077 * conditions (perhaps in addition to plain restriction clauses). So it
1078 * can only be used as the inner path of a nestloop join where the outer
1079 * relation includes all other relids appearing in those joinclauses.
1080 * The set of usable joinclauses, and thus the best inner indexscan,
1081 * thus varies depending on which outer relation we consider; so we have
1082 * to recompute the best such paths for every join. To avoid lots of
1083 * redundant computation, we cache the results of such searches. For
1084 * each relation we compute the set of possible otherrelids (all relids
1085 * appearing in joinquals that could become indexquals for this table).
1086 * Two outer relations whose relids have the same intersection with this
1087 * set will have the same set of available joinclauses and thus the same
1088 * best inner indexscans for the inner relation. By taking the intersection
1089 * before scanning the cache, we avoid recomputing when considering
1090 * join rels that differ only by the inclusion of irrelevant other rels.
1092 * The search key also includes a bool showing whether the join being
1093 * considered is an outer join. Since we constrain the join order for
1094 * outer joins, I believe that this bool can only have one possible value
1095 * for any particular lookup key; but store it anyway to avoid confusion.
1098 typedef struct InnerIndexscanInfo
1101 /* The lookup key: */
1102 Relids other_relids; /* a set of relevant other relids */
1103 bool isouterjoin; /* true if join is outer */
1104 /* Best paths for this lookup key (NULL if no available indexscans): */
1105 Path *cheapest_startup_innerpath; /* cheapest startup cost */
1106 Path *cheapest_total_innerpath; /* cheapest total cost */
1107 } InnerIndexscanInfo;
1110 * Placeholder node for an expression to be evaluated below the top level
1111 * of a plan tree. This is used during planning to represent the contained
1112 * expression. At the end of the planning process it is replaced by either
1113 * the contained expression or a Var referring to a lower-level evaluation of
1114 * the contained expression. Typically the evaluation occurs below an outer
1115 * join, and Var references above the outer join might thereby yield NULL
1116 * instead of the expression value.
1118 * Although the planner treats this as an expression node type, it is not
1119 * recognized by the parser or executor, so we declare it here rather than
1123 typedef struct PlaceHolderVar
1126 Expr *phexpr; /* the represented expression */
1127 Relids phrels; /* base relids syntactically within expr src */
1128 Index phid; /* ID for PHV (unique within planner run) */
1129 Index phlevelsup; /* > 0 if PHV belongs to outer query */
1133 * "Special join" info.
1135 * One-sided outer joins constrain the order of joining partially but not
1136 * completely. We flatten such joins into the planner's top-level list of
1137 * relations to join, but record information about each outer join in a
1138 * SpecialJoinInfo struct. These structs are kept in the PlannerInfo node's
1141 * Similarly, semijoins and antijoins created by flattening IN (subselect)
1142 * and EXISTS(subselect) clauses create partial constraints on join order.
1143 * These are likewise recorded in SpecialJoinInfo structs.
1145 * We make SpecialJoinInfos for FULL JOINs even though there is no flexibility
1146 * of planning for them, because this simplifies make_join_rel()'s API.
1148 * min_lefthand and min_righthand are the sets of base relids that must be
1149 * available on each side when performing the special join. lhs_strict is
1150 * true if the special join's condition cannot succeed when the LHS variables
1151 * are all NULL (this means that an outer join can commute with upper-level
1152 * outer joins even if it appears in their RHS). We don't bother to set
1153 * lhs_strict for FULL JOINs, however.
1155 * It is not valid for either min_lefthand or min_righthand to be empty sets;
1156 * if they were, this would break the logic that enforces join order.
1158 * syn_lefthand and syn_righthand are the sets of base relids that are
1159 * syntactically below this special join. (These are needed to help compute
1160 * min_lefthand and min_righthand for higher joins.)
1162 * delay_upper_joins is set TRUE if we detect a pushed-down clause that has
1163 * to be evaluated after this join is formed (because it references the RHS).
1164 * Any outer joins that have such a clause and this join in their RHS cannot
1165 * commute with this join, because that would leave noplace to check the
1166 * pushed-down clause. (We don't track this for FULL JOINs, either.)
1168 * join_quals is an implicit-AND list of the quals syntactically associated
1169 * with the join (they may or may not end up being applied at the join level).
1170 * This is just a side list and does not drive actual application of quals.
1171 * For JOIN_SEMI joins, this is cleared to NIL in create_unique_path() if
1172 * the join is found not to be suitable for a uniqueify-the-RHS plan.
1174 * jointype is never JOIN_RIGHT; a RIGHT JOIN is handled by switching
1175 * the inputs to make it a LEFT JOIN. So the allowed values of jointype
1176 * in a join_info_list member are only LEFT, FULL, SEMI, or ANTI.
1178 * For purposes of join selectivity estimation, we create transient
1179 * SpecialJoinInfo structures for regular inner joins; so it is possible
1180 * to have jointype == JOIN_INNER in such a structure, even though this is
1181 * not allowed within join_info_list. We also create transient
1182 * SpecialJoinInfos with jointype == JOIN_INNER for outer joins, since for
1183 * cost estimation purposes it is sometimes useful to know the join size under
1184 * plain innerjoin semantics. Note that lhs_strict, delay_upper_joins, and
1185 * join_quals are not set meaningfully within such structs.
1188 typedef struct SpecialJoinInfo
1191 Relids min_lefthand; /* base relids in minimum LHS for join */
1192 Relids min_righthand; /* base relids in minimum RHS for join */
1193 Relids syn_lefthand; /* base relids syntactically within LHS */
1194 Relids syn_righthand; /* base relids syntactically within RHS */
1195 JoinType jointype; /* always INNER, LEFT, FULL, SEMI, or ANTI */
1196 bool lhs_strict; /* joinclause is strict for some LHS rel */
1197 bool delay_upper_joins; /* can't commute with upper RHS */
1198 List *join_quals; /* join quals, in implicit-AND list format */
1202 * Append-relation info.
1204 * When we expand an inheritable table or a UNION-ALL subselect into an
1205 * "append relation" (essentially, a list of child RTEs), we build an
1206 * AppendRelInfo for each child RTE. The list of AppendRelInfos indicates
1207 * which child RTEs must be included when expanding the parent, and each
1208 * node carries information needed to translate Vars referencing the parent
1209 * into Vars referencing that child.
1211 * These structs are kept in the PlannerInfo node's append_rel_list.
1212 * Note that we just throw all the structs into one list, and scan the
1213 * whole list when desiring to expand any one parent. We could have used
1214 * a more complex data structure (eg, one list per parent), but this would
1215 * be harder to update during operations such as pulling up subqueries,
1216 * and not really any easier to scan. Considering that typical queries
1217 * will not have many different append parents, it doesn't seem worthwhile
1218 * to complicate things.
1220 * Note: after completion of the planner prep phase, any given RTE is an
1221 * append parent having entries in append_rel_list if and only if its
1222 * "inh" flag is set. We clear "inh" for plain tables that turn out not
1223 * to have inheritance children, and (in an abuse of the original meaning
1224 * of the flag) we set "inh" for subquery RTEs that turn out to be
1225 * flattenable UNION ALL queries. This lets us avoid useless searches
1226 * of append_rel_list.
1228 * Note: the data structure assumes that append-rel members are single
1229 * baserels. This is OK for inheritance, but it prevents us from pulling
1230 * up a UNION ALL member subquery if it contains a join. While that could
1231 * be fixed with a more complex data structure, at present there's not much
1232 * point because no improvement in the plan could result.
1235 typedef struct AppendRelInfo
1240 * These fields uniquely identify this append relationship. There can be
1241 * (in fact, always should be) multiple AppendRelInfos for the same
1242 * parent_relid, but never more than one per child_relid, since a given
1243 * RTE cannot be a child of more than one append parent.
1245 Index parent_relid; /* RT index of append parent rel */
1246 Index child_relid; /* RT index of append child rel */
1249 * For an inheritance appendrel, the parent and child are both regular
1250 * relations, and we store their rowtype OIDs here for use in translating
1251 * whole-row Vars. For a UNION-ALL appendrel, the parent and child are
1252 * both subqueries with no named rowtype, and we store InvalidOid here.
1254 Oid parent_reltype; /* OID of parent's composite type */
1255 Oid child_reltype; /* OID of child's composite type */
1258 * The N'th element of this list is a Var or expression representing the
1259 * child column corresponding to the N'th column of the parent. This is
1260 * used to translate Vars referencing the parent rel into references to
1261 * the child. A list element is NULL if it corresponds to a dropped
1262 * column of the parent (this is only possible for inheritance cases, not
1263 * UNION ALL). The list elements are always simple Vars for inheritance
1264 * cases, but can be arbitrary expressions in UNION ALL cases.
1266 * Notice we only store entries for user columns (attno > 0). Whole-row
1267 * Vars are special-cased, and system columns (attno < 0) need no special
1268 * translation since their attnos are the same for all tables.
1270 * Caution: the Vars have varlevelsup = 0. Be careful to adjust as needed
1271 * when copying into a subquery.
1273 List *translated_vars; /* Expressions in the child's Vars */
1276 * We store the parent table's OID here for inheritance, or InvalidOid for
1277 * UNION ALL. This is only needed to help in generating error messages if
1278 * an attempt is made to reference a dropped parent column.
1280 Oid parent_reloid; /* OID of parent relation */
1284 * For each distinct placeholder expression generated during planning, we
1285 * store a PlaceHolderInfo node in the PlannerInfo node's placeholder_list.
1286 * This stores info that is needed centrally rather than in each copy of the
1287 * PlaceHolderVar. The phid fields identify which PlaceHolderInfo goes with
1288 * each PlaceHolderVar. Note that phid is unique throughout a planner run,
1289 * not just within a query level --- this is so that we need not reassign ID's
1290 * when pulling a subquery into its parent.
1292 * The idea is to evaluate the expression at (only) the ph_eval_at join level,
1293 * then allow it to bubble up like a Var until the ph_needed join level.
1294 * ph_needed has the same definition as attr_needed for a regular Var.
1296 * We create a PlaceHolderInfo only after determining that the PlaceHolderVar
1297 * is actually referenced in the plan tree.
1300 typedef struct PlaceHolderInfo
1304 Index phid; /* ID for PH (unique within planner run) */
1305 PlaceHolderVar *ph_var; /* copy of PlaceHolderVar tree */
1306 Relids ph_eval_at; /* lowest level we can evaluate value at */
1307 Relids ph_needed; /* highest level the value is needed at */
1308 int32 ph_width; /* estimated attribute width */
1312 * glob->paramlist keeps track of the PARAM_EXEC slots that we have decided
1313 * we need for the query. At runtime these slots are used to pass values
1314 * either down into subqueries (for outer references in subqueries) or up out
1315 * of subqueries (for the results of a subplan). The n'th entry in the list
1316 * (n counts from 0) corresponds to Param->paramid = n.
1318 * Each paramlist item shows the absolute query level it is associated with,
1319 * where the outermost query is level 1 and nested subqueries have higher
1320 * numbers. The item the parameter slot represents can be one of three kinds:
1322 * A Var: the slot represents a variable of that level that must be passed
1323 * down because subqueries have outer references to it. The varlevelsup
1324 * value in the Var will always be zero.
1326 * An Aggref (with an expression tree representing its argument): the slot
1327 * represents an aggregate expression that is an outer reference for some
1328 * subquery. The Aggref itself has agglevelsup = 0, and its argument tree
1329 * is adjusted to match in level.
1331 * A Param: the slot holds the result of a subplan (it is a setParam item
1332 * for that subplan). The absolute level shown for such items corresponds
1333 * to the parent query of the subplan.
1335 * Note: we detect duplicate Var parameters and coalesce them into one slot,
1336 * but we do not do this for Aggref or Param slots.
1338 typedef struct PlannerParamItem
1342 Node *item; /* the Var, Aggref, or Param */
1343 Index abslevel; /* its absolute query level */
1346 #endif /* RELATION_H */