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Refactor planner's pathkeys data structure to create a separate, explicit

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representation of equivalence classes of variables.  This is an extensive
rewrite, but it brings a number of benefits:
* planner no longer fails in the presence of "incomplete" operator families
that don't offer operators for every possible combination of datatypes.
* avoid generating and then discarding redundant equality clauses.
* remove bogus assumption that derived equalities always use operators
named "=".
* mergejoins can work with a variety of sort orders (e.g., descending) now,
instead of tying each mergejoinable operator to exactly one sort order.
* better recognition of redundant sort columns.
* can make use of equalities appearing underneath an outer join.
This commit is contained in:
Tom Lane
2007-01-20 20:45:41 +00:00
parent 2b7334d487
commit f41803bb39
35 changed files with 3882 additions and 2719 deletions
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199
src/include/nodes/relation.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.132 2007/01/10 18:06:04 tgl Exp $
* $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.133 2007/01/20 20:45:40 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -69,7 +69,7 @@ typedef struct PlannerInfo
* does not correspond to a base relation, such as a join RTE or an
* unreferenced view RTE; or if the RelOptInfo hasn't been made yet.
*/
struct RelOptInfo **simple_rel_array; /* All 1-relation RelOptInfos */
struct RelOptInfo **simple_rel_array; /* All 1-rel RelOptInfos */
int simple_rel_array_size; /* allocated size of array */
/*
@@ -84,18 +84,20 @@ typedef struct PlannerInfo
List *join_rel_list; /* list of join-relation RelOptInfos */
struct HTAB *join_rel_hash; /* optional hashtable for join relations */
List *equi_key_list; /* list of lists of equijoined PathKeyItems */
List *eq_classes; /* list of active EquivalenceClasses */
List *left_join_clauses; /* list of RestrictInfos for outer
* join clauses w/nonnullable var on
* left */
List *canon_pathkeys; /* list of "canonical" PathKeys */
List *right_join_clauses; /* list of RestrictInfos for outer
* join clauses w/nonnullable var on
* right */
List *left_join_clauses; /* list of RestrictInfos for
* mergejoinable outer join clauses
* w/nonnullable var on left */
List *full_join_clauses; /* list of RestrictInfos for full
* outer join clauses */
List *right_join_clauses; /* list of RestrictInfos for
* mergejoinable outer join clauses
* w/nonnullable var on right */
List *full_join_clauses; /* list of RestrictInfos for
* mergejoinable full join clauses */
List *oj_info_list; /* list of OuterJoinInfos */
@@ -109,6 +111,8 @@ typedef struct PlannerInfo
List *group_pathkeys; /* groupClause pathkeys, if any */
List *sort_pathkeys; /* sortClause pathkeys, if any */
MemoryContext planner_cxt; /* context holding PlannerInfo */
double total_table_pages; /* # of pages in all tables of query */
double tuple_fraction; /* tuple_fraction passed to query_planner */
@@ -209,7 +213,10 @@ typedef struct PlannerInfo
* baserestrictcost - Estimated cost of evaluating the baserestrictinfo
* clauses at a single tuple (only used for base rels)
* joininfo - List of RestrictInfo nodes, containing info about each
* join clause in which this relation participates
* join clause in which this relation participates (but
* note this excludes clauses that might be derivable from
* EquivalenceClasses)
* has_eclass_joins - flag that EquivalenceClass joins are possible
* index_outer_relids - only used for base rels; set of outer relids
* that participate in indexable joinclauses for this rel
* index_inner_paths - only used for base rels; list of InnerIndexscanInfo
@@ -278,6 +285,7 @@ typedef struct RelOptInfo
QualCost baserestrictcost; /* cost of evaluating the above */
List *joininfo; /* RestrictInfo structures for join clauses
* involving this rel */
bool has_eclass_joins; /* T means joininfo is incomplete */
/* cached info about inner indexscan paths for relation: */
Relids index_outer_relids; /* other relids in indexable join
@@ -349,31 +357,106 @@ typedef struct IndexOptInfo
/*
* PathKeys
* EquivalenceClasses
*
* 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 optimizer/README for more
* information.)
* Whenever we can determine that a mergejoinable equality clause A = B is
* not delayed by any outer join, we create an EquivalenceClass containing
* the expressions A and B to record this knowledge. If we later find another
* equivalence B = C, we add C to the existing EquivalenceClass; this may
* require merging two existing EquivalenceClasses. At the end of the qual
* distribution process, we have sets of values that are known all transitively
* equal to each other, where "equal" is according to the rules of the btree
* operator family(s) shown in ec_opfamilies. (We restrict an EC to contain
* only equalities whose operators belong to the same set of opfamilies. This
* could probably be relaxed, but for now it's not worth the trouble, since
* nearly all equality operators belong to only one btree opclass anyway.)
*
* We also use EquivalenceClasses as the base structure for PathKeys, letting
* us represent knowledge about different sort orderings being equivalent.
* Since every PathKey must reference an EquivalenceClass, we will end up
* with single-member EquivalenceClasses whenever a sort key expression has
* not been equivalenced to anything else. It is also possible that such an
* EquivalenceClass will contain a volatile expression ("ORDER BY random()"),
* which is a case that can't arise otherwise since clauses containing
* volatile functions are never considered mergejoinable. We mark such
* EquivalenceClasses specially to prevent them from being merged with
* ordinary EquivalenceClasses.
*
* We allow equality clauses appearing below the nullable side of an outer join
* to form EquivalenceClasses, but these have a slightly different meaning:
* the included values might be all NULL rather than all the same non-null
* values. See src/backend/optimizer/README for more on that point.
*
* NB: if ec_merged isn't NULL, this class has been merged into another, and
* should be ignored in favor of using the pointed-to class.
*/
typedef struct PathKeyItem
typedef struct EquivalenceClass
{
NodeTag type;
Node *key; /* the item that is ordered */
Oid sortop; /* the ordering operator ('<' op) */
bool nulls_first; /* do NULLs come before normal values? */
List *ec_opfamilies; /* btree operator family OIDs */
List *ec_members; /* list of EquivalenceMembers */
List *ec_sources; /* list of generating RestrictInfos */
Relids ec_relids; /* all relids appearing in ec_members */
bool ec_has_const; /* any pseudoconstants in ec_members? */
bool ec_has_volatile; /* the (sole) member is a volatile expr */
bool ec_below_outer_join; /* equivalence applies below an OJ */
bool ec_broken; /* failed to generate needed clauses? */
struct EquivalenceClass *ec_merged; /* set if merged into another EC */
} EquivalenceClass;
/*
* key typically points to a Var node, ie a relation attribute, but it can
* also point to an arbitrary expression representing the value indexed by
* an index expression.
*/
} PathKeyItem;
/*
* EquivalenceMember - one member expression of an EquivalenceClass
*
* em_is_child signifies that this element was built by transposing a member
* for an inheritance parent relation to represent the corresponding expression
* on an inheritance child. The element should be ignored for all purposes
* except constructing inner-indexscan paths for the child relation. (Other
* types of join are driven from transposed joininfo-list entries.) Note
* that the EC's ec_relids field does NOT include the child relation.
*
* em_datatype is usually the same as exprType(em_expr), but can be
* different when dealing with a binary-compatible opfamily; in particular
* anyarray_ops would never work without this. Use em_datatype when
* looking up a specific btree operator to work with this expression.
*/
typedef struct EquivalenceMember
{
NodeTag type;
Expr *em_expr; /* the expression represented */
Relids em_relids; /* all relids appearing in em_expr */
bool em_is_const; /* expression is pseudoconstant? */
bool em_is_child; /* derived version for a child relation? */
Oid em_datatype; /* the "nominal type" used by the opfamily */
} EquivalenceMember;
/*
* PathKeys
*
* The sort ordering of a path is represented by a list of PathKey nodes.
* An empty list implies no known ordering. Otherwise the first item
* represents the primary sort key, the second the first secondary sort key,
* etc. The value being sorted is represented by linking to an
* EquivalenceClass containing that value and including pk_opfamily among its
* ec_opfamilies. This is a convenient method because it makes it trivial
* to detect equivalent and closely-related orderings. (See optimizer/README
* for more information.)
*
* Note: pk_strategy is either BTLessStrategyNumber (for ASC) or
* BTGreaterStrategyNumber (for DESC). We assume that all ordering-capable
* index types will use btree-compatible strategy numbers.
*/
typedef struct PathKey
{
NodeTag type;
EquivalenceClass *pk_eclass; /* the value that is ordered */
Oid pk_opfamily; /* btree opfamily defining the ordering */
int pk_strategy; /* sort direction (ASC or DESC) */
bool pk_nulls_first; /* do NULLs come before normal values? */
} PathKey;
/*
* Type "Path" is used as-is for sequential-scan paths. For other
@@ -398,7 +481,7 @@ typedef struct Path
Cost total_cost; /* total cost (assuming all tuples fetched) */
List *pathkeys; /* sort ordering of path's output */
/* pathkeys is a List of Lists of PathKeyItem nodes; see above */
/* pathkeys is a List of PathKey nodes; see above */
} Path;
/*----------
@@ -618,11 +701,7 @@ 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. The parallel arrays path_mergeFamilies,
* path_mergeStrategies, and path_mergeNullsFirst specify the merge semantics
* for each clause (i.e., define the relevant sort ordering for each clause).
* (XXX is this the most reasonable path-time representation? It's at least
* partially redundant with the pathkeys of the input paths.)
* that will be used in the merge.
*
* Note that the mergeclauses are a subset of the parent relation's
* restriction-clause list. Any join clauses that are not mergejoinable
@@ -639,10 +718,6 @@ typedef struct MergePath
{
JoinPath jpath;
List *path_mergeclauses; /* join clauses to be used for merge */
/* these are arrays, but have the same length as the mergeclauses list: */
Oid *path_mergeFamilies; /* per-clause OIDs of opfamilies */
int *path_mergeStrategies; /* per-clause ordering (ASC or DESC) */
bool *path_mergeNullsFirst; /* per-clause nulls ordering */
List *outersortkeys; /* keys for explicit sort, if any */
List *innersortkeys; /* keys for explicit sort, if any */
} MergePath;
@@ -696,6 +771,15 @@ typedef struct HashPath
* 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.
*
* RestrictInfos that represent equivalence conditions (i.e., mergejoinable
* equalities that are not outerjoin-delayed) are handled a bit differently.
* Initially we attach them to the EquivalenceClasses that are derived from
* them. When we construct a scan or join path, we look through all the
* EquivalenceClasses and generate derived RestrictInfos representing the
* minimal set of conditions that need to be checked for this particular scan
* or join to enforce that all members of each EquivalenceClass are in fact
* equal in all rows emitted by the scan or join.
*
* 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
@@ -728,9 +812,9 @@ typedef struct HashPath
*
* 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,
* or hashjoin clauses are limited (e.g., no volatile functions). 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
@@ -758,6 +842,12 @@ typedef struct HashPath
* estimates. Note that a pseudoconstant clause can never be an indexqual
* or merge or hash join clause, so it's of no interest to large parts of
* the planner.
*
* When join clauses are generated from EquivalenceClasses, there may be
* several equally valid ways to enforce join equivalence, of which we need
* apply only one. We mark clauses of this kind by setting parent_ec to
* point to the generating EquivalenceClass. Multiple clauses with the same
* parent_ec in the same join are redundant.
*/
typedef struct RestrictInfo
@@ -787,23 +877,22 @@ typedef struct RestrictInfo
/* This field is NULL unless clause is an OR clause: */
Expr *orclause; /* modified clause with RestrictInfos */
/* This field is NULL unless clause is potentially redundant: */
EquivalenceClass *parent_ec; /* generating EquivalenceClass */
/* cache space for cost and selectivity */
QualCost 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 */
Oid mergeopfamily; /* btree opfamily relating these ops */
/* valid if clause is mergejoinable, else NIL */
List *mergeopfamilies; /* opfamilies containing clause operator */
/* 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; NULL if not yet set */
EquivalenceClass *left_ec; /* EquivalenceClass containing lefthand */
EquivalenceClass *right_ec; /* EquivalenceClass containing righthand */
/* 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 */
/* transient workspace for use while considering a specific join path */
bool outer_is_left; /* T = outer var on left, F = on right */
/* valid if clause is hashjoinable, else InvalidOid: */
Oid hashjoinoperator; /* copy of clause operator */