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/* * EquivalenceClasses * * 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, as well as the collation shown * by ec_collation. (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. Similarly, we suppose * that all or none of the input datatypes are collatable, so that a single * collation value is sufficient.) * * 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. Also, for volatile expressions we have * to be careful to match the EquivalenceClass to the correct targetlist * entry: consider SELECT random() AS a, random() AS b ... ORDER BY b,a. * So we record the SortGroupRef of the originating sort clause. * * 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 EquivalenceClass { NodeTag type; List *ec_opfamilies; /* btree操作符族(pg_opfamily)Oids,btree operator family OIDs */ Oid ec_collation; /* 主要用于排序的规则,collation, if datatypes are collatable */ List *ec_members; /* 等价类成员链表,list of EquivalenceMembers */ List *ec_sources; /* 产生等价类的RestrictInfo链表,list of generating RestrictInfos */ List *ec_derives; /* 衍生的RestrictInfo链表,list of derived RestrictInfos */ Relids ec_relids; /* 出现在成员中的所有relids,all relids appearing in ec_members, except * for child members (see below) */ bool ec_has_const; /* 成员中是否存在常量?any pseudoconstants in ec_members? */ bool ec_has_volatile; /* 成员中是否存在易变表达式(如Random等),the (sole) member is a volatile expr */ bool ec_below_outer_join; /* 等价类是否应用于外连接下层?equivalence applies below an OJ */ bool ec_broken; /* 产生所需要的子句是否失败?failed to generate needed clauses? */ Index ec_sortref; /* 源于排序子句的标志,originating sortclause label, or 0 */ Index ec_min_security; /* 最小安全等级,minimum security_level in ec_sources */ Index ec_max_security; /* 最大安全等级,maximum security_level in ec_sources */ struct EquivalenceClass *ec_merged; /* 合并后的等价类,set if merged into another EC */ } EquivalenceClass; /* * If an EC contains a const and isn't below-outer-join, any PathKey depending * on it must be redundant, since there's only one possible value of the key. */ #define EC_MUST_BE_REDUNDANT(eclass) \ ((eclass)->ec_has_const && !(eclass)->ec_below_outer_join) /* * EquivalenceMember - one member expression of an EquivalenceClass * * em_is_child signifies that this element was built by transposing a member * for an appendrel parent relation to represent the corresponding expression * for an appendrel child. These members are used for determining the * pathkeys of scans on the child relation and for explicitly sorting the * child when necessary to build a MergeAppend path for the whole appendrel * tree. An em_is_child member has no impact on the properties of the EC as a * whole; in particular the EC's ec_relids field does NOT include the child * relation. An em_is_child member should never be marked em_is_const nor * cause ec_has_const or ec_has_volatile to be set, either. Thus, em_is_child * members are not really full-fledged members of the EC, but just reflections * or doppelgangers of real members. Most operations on EquivalenceClasses * should ignore em_is_child members, and those that don't should test * em_relids to make sure they only consider relevant members. * * 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; /* 该成员所代表的表达式,the expression represented */ Relids em_relids; /* 出现在表达式中的relids,all relids appearing in em_expr */ Relids em_nullable_relids; /* 低层外连接nullable端的relids,nullable by lower outer joins */ bool em_is_const; /* 常量?expression is pseudoconstant? */ bool em_is_child; /* 子Relation的衍生版本?derived version for a child relation? */ Oid em_datatype; /* 操作族使用到的数据类型,the "nominal type" used by the opfamily */ } EquivalenceMember;
启动gdb,跟踪:
(gdb) b query_planner Breakpoint 3 at 0x7693b5: file planmain.c, line 57.
执行函数deconstruct_jointree,查看root结构
156 joinlist = deconstruct_jointree(root); (gdb) 163 reconsider_outer_join_clauses(root); (gdb) p *root $4 = {type = T_PlannerInfo, parse = 0x2c53ad0, glob = 0x2c8bff8, query_level = 1, parent_root = 0x0, plan_params = 0x0, outer_params = 0x0, simple_rel_array = 0x2c941f8, simple_rel_array_size = 6, simple_rte_array = 0x2c94248, all_baserels = 0x0, nullable_baserels = 0x0, join_rel_list = 0x0, join_rel_hash = 0x0, join_rel_level = 0x0, join_cur_level = 0, init_plans = 0x0, cte_plan_ids = 0x0, multiexpr_params = 0x0, eq_classes = 0x2c960b8, canon_pathkeys = 0x0, left_join_clauses = 0x0, right_join_clauses = 0x0, full_join_clauses = 0x0, join_info_list = 0x0, append_rel_list = 0x0, rowMarks = 0x0, placeholder_list = 0x0, fkey_list = 0x0, query_pathkeys = 0x0, group_pathkeys = 0x0, window_pathkeys = 0x0, distinct_pathkeys = 0x0, sort_pathkeys = 0x0, part_schemes = 0x0, initial_rels = 0x0, upper_rels = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, upper_targets = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, processed_tlist = 0x2c8e3d0, grouping_map = 0x0, minmax_aggs = 0x0, planner_cxt = 0x2b9fde0, total_table_pages = 0, tuple_fraction = 0, limit_tuples = -1, qual_security_level = 0, inhTargetKind = INHKIND_NONE, hasJoinRTEs = true, hasLateralRTEs = true, hasDeletedRTEs = false, hasHavingQual = false, hasPseudoConstantQuals = false, hasRecursion = false, wt_param_id = -1, non_recursive_path = 0x0, curOuterRels = 0x0, curOuterParams = 0x0, join_search_private = 0x0, partColsUpdated = false}
root->eq_classes是等价类链表,其中的元素是等价类
(gdb) p *root->eq_classes $1 = {type = T_List, length = 2, head = 0x2c6daf8, tail = 0x2c6ddf8} (gdb) set $ec1=(EquivalenceClass *)root->eq_classes->head->data.ptr_value (gdb) set $ec2=(EquivalenceClass *)root->eq_classes->head->next->data.ptr_value (gdb) p *$ec1 $4 = {type = T_EquivalenceClass, ec_opfamilies = 0x2c6d980, ec_collation = 100, ec_members = 0x2c6da58, ec_sources = 0x2c6d9f0, ec_derives = 0x0, ec_relids = 0x2c6da20, ec_has_const = false, ec_has_volatile = false, ec_below_outer_join = false, ec_broken = false, ec_sortref = 0, ec_min_security = 0, ec_max_security = 0, ec_merged = 0x0} (gdb) p *$ec2 $5 = {type = T_EquivalenceClass, ec_opfamilies = 0x2c6dc30, ec_collation = 100, ec_members = 0x2c6dd58, ec_sources = 0x2c6dca0, ec_derives = 0x0, ec_relids = 0x2c6dd20, ec_has_const = true, ec_has_volatile = false, ec_below_outer_join = false, ec_broken = false, ec_sortref = 0, ec_min_security = 0, ec_max_security = 0, ec_merged = 0x0} (gdb)
第1个等价类信息
ec_opfamilies
(gdb) p *$ec1->ec_opfamilies $6 = {type = T_OidList, length = 2, head = 0x2c6d960, tail = 0x2c6d9b0} (gdb) p $ec1->ec_opfamilies->head->data.oid_value $7 = 1994 (gdb) p $ec1->ec_opfamilies->head->next->data.oid_value $8 = 2095 (gdb)
数据字典中相应的记录:
testdb=# select * from pg_opfamily where oid=2095; opfmethod | opfname | opfnamespace | opfowner -----------+------------------+--------------+---------- 403 | text_pattern_ops | 11 | 10 (1 row) testdb=# select * from pg_opfamily where oid=1994; opfmethod | opfname | opfnamespace | opfowner -----------+----------+--------------+---------- 403 | text_ops | 11 | 10 (1 row)
ec_members,共有2个元素
第1个元素,是rtindex=3的RTE,属性编号为2的字段,即t_grxx.grbh
(gdb) p *$ec1->ec_members $10 = {type = T_List, length = 2, head = 0x2c6da38, tail = 0x2c6dad8} (gdb) set $ec1_em1=(EquivalenceMember *)$ec1->ec_members->head->data.ptr_value (gdb) set $ec1_em2=(EquivalenceMember *)$ec1->ec_members->head->next->data.ptr_value (gdb) p *$ec1_em1 $13 = {type = T_EquivalenceMember, em_expr = 0x2c69f88, em_relids = 0x2c6d770, em_nullable_relids = 0x0, em_is_const = false, em_is_child = false, em_datatype = 25} (gdb) p *$ec1_em1 $13 = {type = T_EquivalenceMember, em_expr = 0x2c69f88, em_relids = 0x2c6d770, em_nullable_relids = 0x0, em_is_const = false, em_is_child = false, em_datatype = 25} (gdb) p *$ec1_em1->em_expr $14 = {type = T_RelabelType} (gdb) p *(RelabelType *)$ec1_em1->em_expr $15 = {xpr = {type = T_RelabelType}, arg = 0x2c69f38, resulttype = 25, resulttypmod = -1, resultcollid = 100, relabelformat = COERCE_IMPLICIT_CAST, location = -1} (gdb) p *((RelabelType *)$ec1_em1->em_expr)->arg $16 = {type = T_Var} (gdb) p *(Var *)((RelabelType *)$ec1_em1->em_expr)->arg $17 = {xpr = {type = T_Var}, varno = 3, varattno = 2, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0, varnoold = 3, varoattno = 2, location = 136}
第2个元素,是rtindex=4的RTE,属性编号为1的字段,即t_jfxx.grbh
(gdb) p *$ec1_em2->em_expr $28 = {type = T_RelabelType} (gdb) p *(RelabelType *)$ec1_em2->em_expr $29 = {xpr = {type = T_RelabelType}, arg = 0x2c69fd8, resulttype = 25, resulttypmod = -1, resultcollid = 100, relabelformat = COERCE_IMPLICIT_CAST, location = -1} (gdb) p *((RelabelType *)$ec1_em2->em_expr)->arg $30 = {type = T_Var} (gdb) p *(Var *)((RelabelType *)$ec1_em2->em_expr)->arg $31 = {xpr = {type = T_Var}, varno = 4, varattno = 1, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0, varnoold = 4, varoattno = 1, location = 146}
其他信息
(gdb) p *$ec1->ec_sources $34 = {type = T_List, length = 1, head = 0x2c6d9d0, tail = 0x2c6d9d0} (gdb) p *(Node *)$ec1->ec_sources->head->data.ptr_value $35 = {type = T_RestrictInfo} (gdb) p *(RestrictInfo *)$ec1->ec_sources->head->data.ptr_value $36 = {type = T_RestrictInfo, clause = 0x2c6a098, is_pushed_down = true, outerjoin_delayed = false, can_join = true, pseudoconstant = false, leakproof = false, security_level = 0, clause_relids = 0x2c6d7a0, required_relids = 0x2c6d758, outer_relids = 0x0, nullable_relids = 0x0, left_relids = 0x2c6d770, right_relids = 0x2c6d788, orclause = 0x0, parent_ec = 0x0, eval_cost = {startup = -1, per_tuple = 0}, norm_selec = -1, outer_selec = -1, mergeopfamilies = 0x2c6d980, left_ec = 0x2c6ce68, right_ec = 0x2c6ce68, left_em = 0x2c6d890, right_em = 0x2c6da88, scansel_cache = 0x0, outer_is_left = false, hashjoinoperator = 0, left_bucketsize = -1, right_bucketsize = -1, left_mcvfreq = -1, right_mcvfreq = -1} (gdb) p *$ec1->ec_relids $38 = {nwords = 1, words = 0x2c6da24} #即3号和4号RTE (gdb) p $ec1->ec_relids->words[0] $39 = 24
第2个等价类信息
(gdb) p *$ec2 $41 = {type = T_EquivalenceClass, ec_opfamilies = 0x2c6dc30, ec_collation = 100, ec_members = 0x2c6dd58, ec_sources = 0x2c6dca0, ec_derives = 0x0, ec_relids = 0x2c6dd20, ec_has_const = true, ec_has_volatile = false, ec_below_outer_join = false, ec_broken = false, ec_sortref = 0, ec_min_security = 0, ec_max_security = 0, ec_merged = 0x0}
ec_opfamilies,与第1个等价类的信息一致
(gdb) p *$ec2->ec_opfamilies $42 = {type = T_OidList, length = 2, head = 0x2c6dc60, tail = 0x2c6dc10} (gdb) p $ec2->ec_opfamilies->head->data.oid_value $43 = 1994 (gdb) p $ec2->ec_opfamilies->head->next->data.oid_value $44 = 2095
ec_members,有3个元素
(gdb) p *$ec2->ec_members $46 = {type = T_List, length = 3, head = 0x2c6dd38, tail = 0x2c6df20} (gdb) set $ec2_em1=(EquivalenceMember *)$ec2->ec_members->head->data.ptr_value (gdb) set $ec2_em2=(EquivalenceMember *)$ec2->ec_members->head->next->data.ptr_value (gdb) set $ec2_em3=(EquivalenceMember *)$ec2->ec_members->head->next->next->data.ptr_value
第1个元素,3号RTE,属性编号为1的字段,即t_grxx.dwbh
(gdb) p *$ec2_em1 $47 = {type = T_EquivalenceMember, em_expr = 0x2c69d58, em_relids = 0x2c6dbc8, em_nullable_relids = 0x0, em_is_const = false, em_is_child = false, em_datatype = 25} (gdb) p *$ec2_em1->em_expr $48 = {type = T_RelabelType} (gdb) p *(RelabelType *)$ec2_em1->em_expr $49 = {xpr = {type = T_RelabelType}, arg = 0x2c69d08, resulttype = 25, resulttypmod = -1, resultcollid = 100, relabelformat = COERCE_IMPLICIT_CAST, location = -1} (gdb) p *(Var *)((RelabelType *)$ec2_em1->em_expr)->arg $50 = {xpr = {type = T_Var}, varno = 3, varattno = 1, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0, varnoold = 3, varoattno = 1, location = 115}
第2个元素
(gdb) p *$ec2_em2,1号RTE,属性编号为2的字段,即t_dwxx.dwbh $52 = {type = T_EquivalenceMember, em_expr = 0x2c69e28, em_relids = 0x2c6dbe0, em_nullable_relids = 0x0, em_is_const = false, em_is_child = false, em_datatype = 25} (gdb) p *$ec2_em2->em_expr $53 = {type = T_RelabelType} (gdb) p *(Var *)((RelabelType *)$ec2_em2->em_expr)->arg $54 = {xpr = {type = T_Var}, varno = 1, varattno = 2, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0, varnoold = 1, varoattno = 2, location = 125}
第3个元素,是一个常量,即'1001'
(gdb) p *$ec2_em3 $55 = {type = T_EquivalenceMember, em_expr = 0x2c6a498, em_relids = 0x0, em_nullable_relids = 0x0, em_is_const = true, em_is_child = false, em_datatype = 25} (gdb) p *$ec2_em3->em_expr $56 = {type = T_Const} (gdb) p *((Const *)$ec2_em2->em_expr)->arg (gdb) p *(Const *)$ec2_em3->em_expr $58 = {xpr = {type = T_Const}, consttype = 25, consttypmod = -1, constcollid = 100, constlen = -1, constvalue = 46517720, constisnull = false, constbyval = false, location = 172}
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