/*------------------------------------------------------------------------- * * relation.h * Definitions for planner's internal data structures. * * * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * $Id: relation.h,v 1.74 2002/12/12 15:49:40 tgl Exp $ * *------------------------------------------------------------------------- */ #ifndef RELATION_H #define RELATION_H #include "access/sdir.h" #include "nodes/parsenodes.h" /* * Relids * List of relation identifiers (indexes into the rangetable). * * Note: these are lists of integers, not Nodes. */ typedef List *Relids; /* * When looking for a "cheapest path", this enum specifies whether we want * cheapest startup cost or cheapest total cost. */ typedef enum CostSelector { STARTUP_COST, TOTAL_COST } CostSelector; /*---------- * RelOptInfo * Per-relation information for planning/optimization * * For planning purposes, a "base rel" is either a plain relation (a table) * or the output of a sub-SELECT that appears in the range table. * In either case it is uniquely identified by an RT index. A "joinrel" * is the joining of two or more base rels. A joinrel is identified by * the set of RT indexes for its component baserels. We create RelOptInfo * nodes for each baserel and joinrel, and store them in the Query's * base_rel_list and join_rel_list respectively. * * Note that there is only one joinrel for any given set of component * baserels, no matter what order we assemble them in; so an unordered * set is the right datatype to identify it with. * * We also have "other rels", which are like base rels in that they refer to * single RT indexes; but they are not part of the join tree, and are stored * in other_rel_list not base_rel_list. An otherrel is created for each * join RTE as an aid in processing Vars that refer to the join's outputs, * but it serves no other purpose in planning. It is important not to * confuse this otherrel with the joinrel that represents the matching set * of base relations. * * A second category of otherrels are those made for child relations of an * inheritance scan (SELECT FROM foo*). The parent table's RTE and * corresponding baserel represent the whole result of the inheritance scan. * The planner creates separate RTEs and associated RelOptInfos for each child * table (including the parent table, in its capacity as a member of the * inheritance set). These RelOptInfos are physically identical to baserels, * but are otherrels because they are not in the main join tree. These added * RTEs and otherrels are used to plan the scans of the individual tables in * the inheritance set; then the parent baserel is given an Append plan * comprising the best plans for the individual child tables. * * Parts of this data structure are specific to various scan and join * mechanisms. It didn't seem worth creating new node types for them. * * relids - List of base-relation identifiers; it is a base relation * if there is just one, a join relation if more than one * rows - estimated number of tuples in the relation after restriction * clauses have been applied (ie, output rows of a plan for it) * width - avg. number of bytes per tuple in the relation after the * appropriate projections have been done (ie, output width) * targetlist - List of TargetEntry nodes for the attributes we need * to output from this relation * pathlist - List of Path nodes, one for each potentially useful * method of generating the relation * cheapest_startup_path - the pathlist member with lowest startup cost * (regardless of its ordering) * cheapest_total_path - the pathlist member with lowest total cost * (regardless of its ordering) * pruneable - flag to let the planner know whether it can prune the * pathlist of this RelOptInfo or not. * * If the relation is a base relation it will have these fields set: * * rtekind - distinguishes plain relation, subquery, or function RTE * indexlist - list of IndexOptInfo nodes for relation's indexes * (always NIL if it's not a table) * pages - number of disk pages in relation (zero if not a table) * tuples - number of tuples in relation (not considering restrictions) * subplan - plan for subquery (NULL if it's not a subquery) * * Note: for a subquery, tuples and subplan are not set immediately * upon creation of the RelOptInfo object; they are filled in when * set_base_rel_pathlist processes the object. * * For otherrels that are inheritance children, these fields are filled * in just as for a baserel. In otherrels for join RTEs, these fields * are empty --- the only useful field of a join otherrel is its * outerjoinset. * * If the relation is a join relation it will have these fields set: * * joinrti - RT index of corresponding JOIN RTE, if any; 0 if none * joinrteids - List of RT indexes of JOIN RTEs included in this join * (including joinrti) * * The presence of the remaining fields depends on the restrictions * and joins that the relation participates in: * * baserestrictinfo - List of RestrictInfo nodes, containing info about * each qualification clause in which this relation * participates (only used for base rels) * baserestrictcost - Estimated cost of evaluating the baserestrictinfo * clauses at a single tuple (only used for base rels) * outerjoinset - For a base rel: if the rel appears within the nullable * side of an outer join, the list of all relids * participating in the highest such outer join; else NIL. * For a join otherrel: the list of all baserel relids * syntactically within the join. Otherwise, unused. * joininfo - List of JoinInfo nodes, containing info about each join * clause in which this relation participates * index_outer_relids - only used for base rels; list of outer relids * that participate in indexable joinclauses for this rel * index_inner_paths - only used for base rels; list of InnerIndexscanInfo * nodes showing best indexpaths for various subsets of * index_outer_relids. * * Note: Keeping a restrictinfo list in the RelOptInfo is useful only for * base rels, because for a join rel the set of clauses that are treated as * restrict clauses varies depending on which sub-relations we choose to join. * (For example, in a 3-base-rel join, a clause relating rels 1 and 2 must be * treated as a restrictclause if we join {1} and {2 3} to make {1 2 3}; but * if we join {1 2} and {3} then that clause will be a restrictclause in {1 2} * and should not be processed again at the level of {1 2 3}.) Therefore, * the restrictinfo list in the join case appears in individual JoinPaths * (field joinrestrictinfo), not in the parent relation. But it's OK for * the RelOptInfo to store the joininfo lists, because those are the same * for a given rel no matter how we form it. * * We store baserestrictcost in the RelOptInfo (for base relations) because * we know we will need it at least once (to price the sequential scan) * and may need it multiple times to price index scans. * * outerjoinset is used to ensure correct placement of WHERE clauses that * apply to outer-joined relations; we must not apply such WHERE clauses * until after the outer join is performed. *---------- */ typedef enum RelOptKind { RELOPT_BASEREL, RELOPT_JOINREL, RELOPT_OTHER_JOIN_REL, RELOPT_OTHER_CHILD_REL } RelOptKind; typedef struct RelOptInfo { NodeTag type; RelOptKind reloptkind; /* all relations included in this RelOptInfo */ Relids relids; /* integer list of base relids (rangetable * indexes) */ /* size estimates generated by planner */ double rows; /* estimated number of result tuples */ int width; /* estimated avg width of result tuples */ /* materialization information */ List *targetlist; List *pathlist; /* Path structures */ struct Path *cheapest_startup_path; struct Path *cheapest_total_path; bool pruneable; /* information about a base rel (not set for join rels!) */ RTEKind rtekind; /* RELATION, SUBQUERY, or FUNCTION */ List *indexlist; long pages; double tuples; struct Plan *subplan; /* if subquery */ /* information about a join rel (not set for base rels!) */ Index joinrti; List *joinrteids; /* used by various scans and joins: */ List *baserestrictinfo; /* RestrictInfo structures (if * base rel) */ Cost baserestrictcost; /* cost of evaluating the above */ Relids outerjoinset; /* integer list of base relids */ List *joininfo; /* JoinInfo structures */ /* cached info about inner indexscan paths for relation: */ Relids index_outer_relids; /* other relids in indexable join * clauses */ List *index_inner_paths; /* InnerIndexscanInfo nodes */ /* * Inner indexscans are not in the main pathlist because they are * not usable except in specific join contexts. We use the * index_inner_paths list just to avoid recomputing the best inner * indexscan repeatedly for similar outer relations. See comments * for InnerIndexscanInfo. */ } RelOptInfo; /* * IndexOptInfo * Per-index information for planning/optimization * * Prior to Postgres 7.0, RelOptInfo was used to describe both relations * and indexes, but that created confusion without actually doing anything * useful. So now we have a separate IndexOptInfo struct for indexes. * * ncolumns and nkeys are the same except for a functional index, * wherein ncolumns is 1 (the single function output) while nkeys * is the number of table columns passed to the function. classlist[] * and ordering[] have ncolumns entries, while indexkeys[] has nkeys * entries. * * Note: for historical reasons, the arrays classlist, indexkeys and * ordering have an extra entry that is always zero. Some code scans * until it sees a zero rather than looking at ncolumns or nkeys. */ typedef struct IndexOptInfo { NodeTag type; Oid indexoid; /* OID of the index relation */ /* statistics from pg_class */ long pages; /* number of disk pages in index */ double tuples; /* number of index tuples in index */ /* index descriptor information */ int ncolumns; /* number of columns in index */ int nkeys; /* number of keys used by index */ Oid *classlist; /* OIDs of operator classes for columns */ int *indexkeys; /* column numbers of index's keys */ Oid *ordering; /* OIDs of sort operators for each column */ Oid relam; /* OID of the access method (in pg_am) */ RegProcedure amcostestimate; /* OID of the access method's cost fcn */ Oid indproc; /* OID of func if functional index, else 0 */ List *indpred; /* predicate if a partial index, else NIL */ bool unique; /* true if a unique index */ /* cached info about inner indexscan paths for index */ Relids outer_relids; /* other relids in usable join clauses */ List *inner_paths; /* List of InnerIndexscanInfo nodes */ } IndexOptInfo; /* * A Var is considered to belong to a relation if it's either from one * of the actual base rels making up the relation, or it's a join alias * var that is included in the relation. */ #define VARISRELMEMBER(varno,rel) (intMember((varno), (rel)->relids) || \ intMember((varno), (rel)->joinrteids)) /* * PathKeys * * The sort ordering of a path is represented by a list of sublists of * PathKeyItem nodes. An empty list implies no known ordering. Otherwise * the first sublist represents the primary sort key, the second the * first secondary sort key, etc. Each sublist contains one or more * PathKeyItem nodes, each of which can be taken as the attribute that * appears at that sort position. (See the top of optimizer/path/pathkeys.c * for more information.) */ typedef struct PathKeyItem { NodeTag type; Node *key; /* the item that is ordered */ Oid sortop; /* the ordering operator ('<' op) */ /* * key typically points to a Var node, ie a relation attribute, but it * can also point to a FuncExpr clause representing the value indexed by a * functional index. Someday we might allow arbitrary expressions as * path keys, so don't assume more than you must. */ } PathKeyItem; /* * Type "Path" is used as-is for sequential-scan paths. For other * path types it is the first component of a larger struct. * * Note: "pathtype" is the NodeTag of the Plan node we could build from this * Path. It is partially redundant with the Path's NodeTag, but allows us * to use the same Path type for multiple Plan types where there is no need * to distinguish the Plan type during path processing. */ typedef struct Path { NodeTag type; RelOptInfo *parent; /* the relation this path can build */ /* estimated execution costs for path (see costsize.c for more info) */ Cost startup_cost; /* cost expended before fetching any * tuples */ Cost total_cost; /* total cost (assuming all tuples * fetched) */ NodeTag pathtype; /* tag identifying scan/join method */ List *pathkeys; /* sort ordering of path's output */ /* pathkeys is a List of Lists of PathKeyItem nodes; see above */ } Path; /*---------- * IndexPath represents an index scan. Although an indexscan can only read * a single relation, it can scan it more than once, potentially using a * different index during each scan. The result is the union (OR) of all the * tuples matched during any scan. (The executor is smart enough not to return * the same tuple more than once, even if it is matched in multiple scans.) * * 'indexinfo' is a list of IndexOptInfo nodes, one per scan to be performed. * * 'indexqual' is a list of index qualifications, also one per scan. * Each entry in 'indexqual' is a sublist of qualification expressions with * implicit AND semantics across the sublist items. Only expressions that * are usable as indexquals (as determined by indxpath.c) may appear here. * NOTE that the semantics of the top-level list in 'indexqual' is OR * combination, while the sublists are implicitly AND combinations! * Also note that indexquals lists do not contain RestrictInfo nodes, * just bare clause expressions. * * 'indexscandir' is one of: * ForwardScanDirection: forward scan of an ordered index * BackwardScanDirection: backward scan of an ordered index * NoMovementScanDirection: scan of an unordered index, or don't care * (The executor doesn't care whether it gets ForwardScanDirection or * NoMovementScanDirection for an indexscan, but the planner wants to * distinguish ordered from unordered indexes for building pathkeys.) * * 'rows' is the estimated result tuple count for the indexscan. This * is the same as path.parent->rows for a simple indexscan, but it is * different for a nestloop inner scan, because the additional indexquals * coming from join clauses make the scan more selective than the parent * rel's restrict clauses alone would do. *---------- */ typedef struct IndexPath { Path path; List *indexinfo; List *indexqual; ScanDirection indexscandir; double rows; /* estimated number of result tuples */ } IndexPath; /* * TidPath represents a scan by TID */ typedef struct TidPath { Path path; List *tideval; /* qual(s) involving CTID = something */ } TidPath; /* * AppendPath represents an Append plan, ie, successive execution of * several member plans. Currently it is only used to handle expansion * of inheritance trees. */ typedef struct AppendPath { Path path; List *subpaths; /* list of component Paths */ } AppendPath; /* * ResultPath represents use of a Result plan node, either to compute a * variable-free targetlist or to gate execution of a subplan with a * one-time (variable-free) qual condition. Note that in the former case * path.parent will be NULL; in the latter case it is copied from the subpath. */ typedef struct ResultPath { Path path; Path *subpath; List *constantqual; } ResultPath; /* * MaterialPath represents use of a Material plan node, i.e., caching of * the output of its subpath. This is used when the subpath is expensive * and needs to be scanned repeatedly, or when we need mark/restore ability * and the subpath doesn't have it. */ typedef struct MaterialPath { Path path; Path *subpath; } MaterialPath; /* * All join-type paths share these fields. */ typedef struct JoinPath { Path path; JoinType jointype; Path *outerjoinpath; /* path for the outer side of the join */ Path *innerjoinpath; /* path for the inner side of the join */ List *joinrestrictinfo; /* RestrictInfos to apply to join */ /* * See the notes for RelOptInfo to understand why joinrestrictinfo is * needed in JoinPath, and can't be merged into the parent RelOptInfo. */ } JoinPath; /* * A nested-loop path needs no special fields. */ typedef JoinPath NestPath; /* * A mergejoin path has these fields. * * path_mergeclauses lists the clauses (in the form of RestrictInfos) * that will be used in the merge. (Before 7.0, this was a list of bare * clause expressions, but we can save on list memory and cost_qual_eval * work by leaving it in the form of a RestrictInfo list.) * * Note that the mergeclauses are a subset of the parent relation's * restriction-clause list. Any join clauses that are not mergejoinable * appear only in the parent's restrict list, and must be checked by a * qpqual at execution time. * * outersortkeys (resp. innersortkeys) is NIL if the outer path * (resp. inner path) is already ordered appropriately for the * mergejoin. If it is not NIL then it is a PathKeys list describing * the ordering that must be created by an explicit sort step. */ typedef struct MergePath { JoinPath jpath; List *path_mergeclauses; /* join clauses to be used for * merge */ List *outersortkeys; /* keys for explicit sort, if any */ List *innersortkeys; /* keys for explicit sort, if any */ } MergePath; /* * A hashjoin path has these fields. * * The remarks above for mergeclauses apply for hashclauses as well. * * Hashjoin does not care what order its inputs appear in, so we have * no need for sortkeys. */ typedef struct HashPath { JoinPath jpath; List *path_hashclauses; /* join clauses used for hashing */ } HashPath; /* * Restriction clause info. * * We create one of these for each AND sub-clause of a restriction condition * (WHERE or JOIN/ON clause). Since the restriction clauses are logically * ANDed, we can use any one of them or any subset of them to filter out * tuples, without having to evaluate the rest. The RestrictInfo node itself * stores data used by the optimizer while choosing the best query plan. * * If a restriction clause references a single base relation, it will appear * in the baserestrictinfo list of the RelOptInfo for that base rel. * * If a restriction clause references more than one base rel, it will * appear in the JoinInfo lists of every RelOptInfo that describes a strict * subset of the base rels mentioned in the clause. The JoinInfo lists are * used to drive join tree building by selecting plausible join candidates. * The clause cannot actually be applied until we have built a join rel * containing all the base rels it references, however. * * When we construct a join rel that includes all the base rels referenced * in a multi-relation restriction clause, we place that clause into the * joinrestrictinfo lists of paths for the join rel, if neither left nor * right sub-path includes all base rels referenced in the clause. The clause * will be applied at that join level, and will not propagate any further up * the join tree. (Note: the "predicate migration" code was once intended to * push restriction clauses up and down the plan tree based on evaluation * costs, but it's dead code and is unlikely to be resurrected in the * foreseeable future.) * * Note that in the presence of more than two rels, a multi-rel restriction * might reach different heights in the join tree depending on the join * sequence we use. So, these clauses cannot be associated directly with * the join RelOptInfo, but must be kept track of on a per-join-path basis. * * When dealing with outer joins we have to be very careful about pushing qual * clauses up and down the tree. An outer join's own JOIN/ON conditions must * be evaluated exactly at that join node, and any quals appearing in WHERE or * in a JOIN above the outer join cannot be pushed down below the outer join. * Otherwise the outer join will produce wrong results because it will see the * wrong sets of input rows. All quals are stored as RestrictInfo nodes * during planning, but there's a flag to indicate whether a qual has been * pushed down to a lower level than its original syntactic placement in the * join tree would suggest. If an outer join prevents us from pushing a qual * down to its "natural" semantic level (the level associated with just the * base rels used in the qual) then the qual will appear in JoinInfo lists * that reference more than just the base rels it actually uses. By * pretending that the qual references all the rels appearing in the outer * join, we prevent it from being evaluated below the outer join's joinrel. * When we do form the outer join's joinrel, we still need to distinguish * those quals that are actually in that join's JOIN/ON condition from those * that appeared higher in the tree and were pushed down to the join rel * because they used no other rels. That's what the ispusheddown flag is for; * it tells us that a qual came from a point above the join of the specific * set of base rels that it uses (or that the JoinInfo structures claim it * uses). A clause that originally came from WHERE will *always* have its * ispusheddown flag set; a clause that came from an INNER JOIN condition, * but doesn't use all the rels being joined, will also have ispusheddown set * because it will get attached to some lower joinrel. * * In general, the referenced clause might be arbitrarily complex. The * kinds of clauses we can handle as indexscan quals, mergejoin clauses, * or hashjoin clauses are fairly limited --- the code for each kind of * path is responsible for identifying the restrict clauses it can use * and ignoring the rest. Clauses not implemented by an indexscan, * mergejoin, or hashjoin will be placed in the plan qual or joinqual field * of the finished Plan node, where they will be enforced by general-purpose * qual-expression-evaluation code. (But we are still entitled to count * their selectivity when estimating the result tuple count, if we * can guess what it is...) */ typedef struct RestrictInfo { NodeTag type; Expr *clause; /* the represented clause of WHERE or JOIN */ bool ispusheddown; /* TRUE if clause was pushed down in level */ /* only used if clause is an OR clause: */ List *subclauseindices; /* indexes matching subclauses */ /* subclauseindices is a List of Lists of IndexOptInfos */ /* cache space for costs (currently only used for join clauses) */ Cost eval_cost; /* eval cost of clause; -1 if not yet set */ Selectivity this_selec; /* selectivity; -1 if not yet set */ /* valid if clause is mergejoinable, else InvalidOid: */ Oid mergejoinoperator; /* copy of clause operator */ Oid left_sortop; /* leftside sortop needed for mergejoin */ Oid right_sortop; /* rightside sortop needed for mergejoin */ /* cache space for mergeclause processing; NIL if not yet set */ List *left_pathkey; /* canonical pathkey for left side */ List *right_pathkey; /* canonical pathkey for right side */ /* cache space for mergeclause processing; -1 if not yet set */ Selectivity left_mergescansel; /* fraction of left side to scan */ Selectivity right_mergescansel; /* fraction of right side to scan */ /* valid if clause is hashjoinable, else InvalidOid: */ Oid hashjoinoperator; /* copy of clause operator */ /* cache space for hashclause processing; -1 if not yet set */ Selectivity left_bucketsize; /* avg bucketsize of left side */ Selectivity right_bucketsize; /* avg bucketsize of right side */ } RestrictInfo; /* * Join clause info. * * We make a list of these for each RelOptInfo, containing info about * all the join clauses this RelOptInfo participates in. (For this * purpose, a "join clause" is a WHERE clause that mentions both vars * belonging to this relation and vars belonging to relations not yet * joined to it.) We group these clauses according to the set of * other base relations (unjoined relations) mentioned in them. * There is one JoinInfo for each distinct set of unjoined_relids, * and its jinfo_restrictinfo lists the clause(s) that use that set * of other relations. */ typedef struct JoinInfo { NodeTag type; Relids unjoined_relids; /* some rels not yet part of my RelOptInfo */ List *jinfo_restrictinfo; /* relevant RestrictInfos */ } JoinInfo; /* * Inner indexscan info. * * An inner indexscan is one that uses one or more joinclauses as index * conditions (perhaps in addition to plain restriction clauses). So it * can only be used as the inner path of a nestloop join where the outer * relation includes all other relids appearing in those joinclauses. * The set of usable joinclauses, and thus the best inner indexscan, * thus varies depending on which outer relation we consider; so we have * to recompute the best such path for every join. To avoid lots of * redundant computation, we cache the results of such searches. For * each index we compute the set of possible otherrelids (all relids * appearing in joinquals that could become indexquals for this index). * Two outer relations whose relids have the same intersection with this * set will have the same set of available joinclauses and thus the same * best inner indexscan for that index. Similarly, for each base relation, * we form the union of the per-index otherrelids sets. Two outer relations * with the same intersection with that set will have the same best overall * inner indexscan for the base relation. We use lists of InnerIndexscanInfo * nodes to cache the results of these searches at both the index and * relation level. * * The search key also includes a bool showing whether the join being * considered is an outer join. Since we constrain the join order for * outer joins, I believe that this bool can only have one possible value * for any particular base relation; but store it anyway to avoid confusion. */ typedef struct InnerIndexscanInfo { NodeTag type; /* The lookup key: */ Relids other_relids; /* a set of relevant other relids */ bool isouterjoin; /* true if join is outer */ /* Best path for this lookup key: */ Path *best_innerpath; /* best inner indexscan, or NULL if none */ } InnerIndexscanInfo; #endif /* RELATION_H */