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本节大体介绍了动态规划算法实现(standard_join_search)中的join_search_one_level->make_join_rel函数，该函数创建两个rels连接所生成的RelOptInfo,并在RelOptInfo中添加访问路径信息。
RelOptInfo
typedef enum RelOptKind { RELOPT_BASEREL,//基本关系(如基表/子查询等) RELOPT_JOINREL,//连接产生的关系,要注意的是通过连接等方式产生的结果亦可以视为关系 RELOPT_OTHER_MEMBER_REL, RELOPT_OTHER_JOINREL, RELOPT_UPPER_REL,//上层的关系 RELOPT_OTHER_UPPER_REL, RELOPT_DEADREL } RelOptKind; /* * Is the given relation a simple relation i.e a base or "other" member * relation? */ #define IS_SIMPLE_REL(rel) \ ((rel)->reloptkind == RELOPT_BASEREL || \ (rel)->reloptkind == RELOPT_OTHER_MEMBER_REL) /* Is the given relation a join relation? */ #define IS_JOIN_REL(rel) \ ((rel)->reloptkind == RELOPT_JOINREL || \ (rel)->reloptkind == RELOPT_OTHER_JOINREL) /* Is the given relation an upper relation? */ #define IS_UPPER_REL(rel) \ ((rel)->reloptkind == RELOPT_UPPER_REL || \ (rel)->reloptkind == RELOPT_OTHER_UPPER_REL) /* Is the given relation an "other" relation? */ #define IS_OTHER_REL(rel) \ ((rel)->reloptkind == RELOPT_OTHER_MEMBER_REL || \ (rel)->reloptkind == RELOPT_OTHER_JOINREL || \ (rel)->reloptkind == RELOPT_OTHER_UPPER_REL) typedef struct RelOptInfo { NodeTag type;//节点标识 RelOptKind reloptkind;//RelOpt类型 /* all relations included in this RelOptInfo */ Relids relids; /*Relids(rtindex)集合 set of base relids (rangetable indexes) */ /* size estimates generated by planner */ double rows; /*结果元组的估算数量 estimated number of result tuples */ /* per-relation planner control flags */ bool consider_startup; /*是否考虑启动成本?是,需要保留启动成本低的路径 keep cheap-startup-cost paths? */ bool consider_param_startup; /*是否考虑参数化?的路径 ditto, for parameterized paths? */ bool consider_parallel; /*是否考虑并行处理路径 consider parallel paths? */ /* default result targetlist for Paths scanning this relation */ struct PathTarget *reltarget; /*扫描该Relation时默认的结果 list of Vars/Exprs, cost, width */ /* materialization information */ List *pathlist; /*访问路径链表 Path structures */ List *ppilist; /*路径链表中使用参数化路径进行 ParamPathInfos used in pathlist */ List *partial_pathlist; /* partial Paths */ struct Path *cheapest_startup_path;//代价最低的启动路径 struct Path *cheapest_total_path;//代价最低的整体路径 struct Path *cheapest_unique_path;//代价最低的获取唯一值的路径 List *cheapest_parameterized_paths;//代价最低的参数化?路径链表 /* parameterization information needed for both base rels and join rels */ /* (see also lateral_vars and lateral_referencers) */ Relids direct_lateral_relids; /*使用lateral语法,需依赖的Relids rels directly laterally referenced */ Relids lateral_relids; /* minimum parameterization of rel */ /* information about a base rel (not set for join rels!) */ //reloptkind=RELOPT_BASEREL时使用的数据结构 Index relid; /* Relation ID */ Oid reltablespace; /* 表空间 containing tablespace */ RTEKind rtekind; /* 基表?子查询?还是函数等等?RELATION, SUBQUERY, FUNCTION, etc */ AttrNumber min_attr; /* 最小的属性编号 smallest attrno of rel (often <0) */ AttrNumber max_attr; /* 最大的属性编号 largest attrno of rel */ Relids *attr_needed; /* 数组 array indexed [min_attr .. max_attr] */ int32 *attr_widths; /* 属性宽度 array indexed [min_attr .. max_attr] */ List *lateral_vars; /* 关系依赖的Vars/PHVs LATERAL Vars and PHVs referenced by rel */ Relids lateral_referencers; /*依赖该关系的Relids rels that reference me laterally */ List *indexlist; /* 该关系的IndexOptInfo链表 list of IndexOptInfo */ List *statlist; /* 统计信息链表 list of StatisticExtInfo */ BlockNumber pages; /* 块数 size estimates derived from pg_class */ double tuples; /* 元组数 */ double allvisfrac; /* ? */ PlannerInfo *subroot; /* 如为子查询,存储子查询的root if subquery */ List *subplan_params; /* 如为子查询,存储子查询的参数 if subquery */ int rel_parallel_workers; /* 并行执行,需要多少个workers? wanted number of parallel workers */ /* Information about foreign tables and foreign joins */ //FWD相关信息 Oid serverid; /* identifies server for the table or join */ Oid userid; /* identifies user to check access as */ bool useridiscurrent; /* join is only valid for current user */ /* use "struct FdwRoutine" to avoid including fdwapi.h here */ struct FdwRoutine *fdwroutine; void *fdw_private; /* cache space for remembering if we have proven this relation unique */ //已知的,可保证唯一的Relids链表 List *unique_for_rels; /* known unique for these other relid * set(s) */ List *non_unique_for_rels; /* 已知的,不唯一的Relids链表 known not unique for these set(s) */ /* used by various scans and joins: */ List *baserestrictinfo; /* 如为基本关系,存储约束条件 RestrictInfo structures (if base rel) */ QualCost baserestrictcost; /* 解析约束表达式的成本? cost of evaluating the above */ Index baserestrict_min_security; /* 最低安全等级 min security_level found in * baserestrictinfo */ List *joininfo; /* 连接语句的约束条件信息 RestrictInfo structures for join clauses * involving this rel */ bool has_eclass_joins; /* 是否存在等价类连接? T means joininfo is incomplete */ /* used by partitionwise joins: */ bool consider_partitionwise_join; /* 分区? consider partitionwise * join paths? (if * partitioned rel) */ Relids top_parent_relids; /* Relids of topmost parents (if "other" * rel) */ /* used for partitioned relations */ //分区表使用 PartitionScheme part_scheme; /* 分区的schema Partitioning scheme. */ int nparts; /* 分区数 number of partitions */ struct PartitionBoundInfoData *boundinfo; /* 分区边界信息 Partition bounds */ List *partition_qual; /* 分区约束 partition constraint */ struct RelOptInfo **part_rels; /* 分区的RelOptInfo数组 Array of RelOptInfos of partitions, * stored in the same order of bounds */ List **partexprs; /* 非空分区键表达式 Non-nullable partition key expressions. */ List **nullable_partexprs; /* 可为空的分区键表达式 Nullable partition key expressions. */ List *partitioned_child_rels; /* RT Indexes链表 List of RT indexes. */ } RelOptInfo; join_search_one_level->...(如make_rels_by_clause_joins)->make_join_rel函数创建两个rels连接所生成的RelOptInfo,并创建访问路径添加到RelOptInfo的pathlist链表中。这里重点介绍make_join_rel函数中的build_join_rel函数,populate_joinrel_with_paths函数下一小节再行介绍.
//---------------------------------------------------- make_join_rel /* * make_join_rel * Find or create a join RelOptInfo that represents the join of * the two given rels, and add to it path information for paths * created with the two rels as outer and inner rel. * (The join rel may already contain paths generated from other * pairs of rels that add up to the same set of base rels.) * 创建两个rels连接所生成的RelOptInfo,并添加访问路径信息. * (新产生的rel可能已经包含从相同的两个rels对所生成的的路径) * * NB: will return NULL if attempted join is not valid. This can happen * when working with outer joins, or with IN or EXISTS clauses that have been * turned into joins. * 注意:如果尝试连接失败,则返回NULL.这可能出现在处理外连接或者已转变为连接的IN/EXISTS子句上 */ RelOptInfo * make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2) { Relids joinrelids; SpecialJoinInfo *sjinfo; bool reversed; SpecialJoinInfo sjinfo_data; RelOptInfo *joinrel; List *restrictlist; /* We should never try to join two overlapping sets of rels. */ Assert(!bms_overlap(rel1->relids, rel2->relids));//两者无交接 /* Construct Relids set that identifies the joinrel. */ joinrelids = bms_union(rel1->relids, rel2->relids);//两个rel涉及的rels /* Check validity and determine join type. */ if (!join_is_legal(root, rel1, rel2, joinrelids, &sjinfo, &reversed))//是否非法 { /* invalid join path */ bms_free(joinrelids); return NULL;//返回 } /* Swap rels if needed to match the join info. */ if (reversed)//位置是否调换 { RelOptInfo *trel = rel1; rel1 = rel2; rel2 = trel; } /* * If it's a plain inner join, then we won't have found anything in * join_info_list. Make up a SpecialJoinInfo so that selectivity * estimation functions will know what's being joined. * 普通的内连接,不需要使用join_info_list, * 构造一个SpecialJoinInfo以便告知选择率估算函数已连接 */ if (sjinfo == NULL) { sjinfo = &sjinfo_data; sjinfo->type = T_SpecialJoinInfo; sjinfo->min_lefthand = rel1->relids; sjinfo->min_righthand = rel2->relids; sjinfo->syn_lefthand = rel1->relids; sjinfo->syn_righthand = rel2->relids; sjinfo->jointype = JOIN_INNER; /* we don't bother trying to make the remaining fields valid */ sjinfo->lhs_strict = false; sjinfo->delay_upper_joins = false; sjinfo->semi_can_btree = false; sjinfo->semi_can_hash = false; sjinfo->semi_operators = NIL; sjinfo->semi_rhs_exprs = NIL; } /* * Find or build the join RelOptInfo, and compute the restrictlist that * goes with this particular joining. * 创建连接生成的新关系RelOptInfo,并为此连接生成限制条件链表 */ joinrel = build_join_rel(root, joinrelids, rel1, rel2, sjinfo, &restrictlist); /* * If we've already proven this join is empty, we needn't consider any * more paths for it. */ if (is_dummy_rel(joinrel)) { bms_free(joinrelids); return joinrel; } /* Add paths to the join relation. */ //为连接生成的新关系构造访问路径 populate_joinrel_with_paths(root, rel1, rel2, joinrel, sjinfo, restrictlist); bms_free(joinrelids);//释放资源 return joinrel;//返回joinrel } //-------------------------------------------------------------------- build_join_rel /* * build_join_rel * Returns relation entry corresponding to the union of two given rels, * creating a new relation entry if none already exists. * 给定两个rels,创建并返回对应这两个rels连接生成的新的Relation * * 'joinrelids' is the Relids set that uniquely identifies the join * 'outer_rel' and 'inner_rel' are relation nodes for the relations to be * joined * 'sjinfo': join context info * 'restrictlist_ptr': result variable. If not NULL, *restrictlist_ptr * receives the list of RestrictInfo nodes that apply to this * particular pair of joinable relations. * joinrelids-与此连接相关的所有relids * outer_rel和inner_rel-构成连接的外表(驱动表)和内表 * sjinfo-连接上下文信息 * restrictlist_ptr-存储结果的变量,如为非NULL值,该指针指向RestrictInfo(约束条件)节点链表 * * restrictlist_ptr makes the routine's API a little grotty, but it saves * duplicated calculation of the restrictlist... */ RelOptInfo * build_join_rel(PlannerInfo *root, Relids joinrelids, RelOptInfo *outer_rel, RelOptInfo *inner_rel, SpecialJoinInfo *sjinfo, List **restrictlist_ptr) { RelOptInfo *joinrel; List *restrictlist; /* This function should be used only for join between parents. */ Assert(!IS_OTHER_REL(outer_rel) && !IS_OTHER_REL(inner_rel)); /* * See if we already have a joinrel for this set of base rels. * 这些基础rels所构成的连接是否已存在? */ joinrel = find_join_rel(root, joinrelids); if (joinrel)//已存在 { /* * Yes, so we only need to figure the restrictlist for this particular * pair of component relations. */ if (restrictlist_ptr) *restrictlist_ptr = build_joinrel_restrictlist(root, joinrel, outer_rel, inner_rel);//如已存在约束条件,则找出相应的信息即可 return joinrel;//返回 } /* * Nope, so make one. * 没有,则构造之 */ joinrel = makeNode(RelOptInfo); joinrel->reloptkind = RELOPT_JOINREL; joinrel->relids = bms_copy(joinrelids); joinrel->rows = 0; /* cheap startup cost is interesting iff not all tuples to be retrieved */ joinrel->consider_startup = (root->tuple_fraction > 0); joinrel->consider_param_startup = false; joinrel->consider_parallel = false; joinrel->reltarget = create_empty_pathtarget(); joinrel->pathlist = NIL; joinrel->ppilist = NIL; joinrel->partial_pathlist = NIL; joinrel->cheapest_startup_path = NULL; joinrel->cheapest_total_path = NULL; joinrel->cheapest_unique_path = NULL; joinrel->cheapest_parameterized_paths = NIL; /* init direct_lateral_relids from children; we'll finish it up below */ joinrel->direct_lateral_relids = bms_union(outer_rel->direct_lateral_relids, inner_rel->direct_lateral_relids); joinrel->lateral_relids = min_join_parameterization(root, joinrel->relids, outer_rel, inner_rel); joinrel->relid = 0; /* indicates not a baserel */ joinrel->rtekind = RTE_JOIN;//RTE_JOIN joinrel->min_attr = 0; joinrel->max_attr = 0; joinrel->attr_needed = NULL; joinrel->attr_widths = NULL; joinrel->lateral_vars = NIL; joinrel->lateral_referencers = NULL; joinrel->indexlist = NIL; joinrel->statlist = NIL; joinrel->pages = 0; joinrel->tuples = 0; joinrel->allvisfrac = 0; joinrel->subroot = NULL; joinrel->subplan_params = NIL; joinrel->rel_parallel_workers = -1; joinrel->serverid = InvalidOid; joinrel->userid = InvalidOid; joinrel->useridiscurrent = false; joinrel->fdwroutine = NULL; joinrel->fdw_private = NULL; joinrel->unique_for_rels = NIL; joinrel->non_unique_for_rels = NIL; joinrel->baserestrictinfo = NIL; joinrel->baserestrictcost.startup = 0; joinrel->baserestrictcost.per_tuple = 0; joinrel->baserestrict_min_security = UINT_MAX; joinrel->joininfo = NIL; joinrel->has_eclass_joins = false; joinrel->consider_partitionwise_join = false; /* might get changed later */ joinrel->top_parent_relids = NULL; joinrel->part_scheme = NULL; joinrel->nparts = 0; joinrel->boundinfo = NULL; joinrel->partition_qual = NIL; joinrel->part_rels = NULL; joinrel->partexprs = NULL; joinrel->nullable_partexprs = NULL; joinrel->partitioned_child_rels = NIL; /* 设置FDW的相关信息,Compute information relevant to the foreign relations. */ set_foreign_rel_properties(joinrel, outer_rel, inner_rel); /* * Create a new tlist containing just the vars that need to be output from * this join (ie, are needed for higher joinclauses or final output). * * 创建一个新的投影列链表,只包含该连接的输出 * NOTE: the tlist order for a join rel will depend on which pair of outer * and inner rels we first try to build it from. But the contents should * be the same regardless. */ build_joinrel_tlist(root, joinrel, outer_rel);//连接外表 build_joinrel_tlist(root, joinrel, inner_rel);//连接内表 add_placeholders_to_joinrel(root, joinrel, outer_rel, inner_rel);//添加PHV /* * add_placeholders_to_joinrel also took care of adding the ph_lateral * sets of any PlaceHolderVars computed here to direct_lateral_relids, so * now we can finish computing that. This is much like the computation of * the transitively-closed lateral_relids in min_join_parameterization, * except that here we *do* have to consider the added PHVs. * add_placeholders_to_joinrel函数将这里产生的PlaceHolderVars的ph_lateral集合 * 添加到direct_lateral_relids中以完成最终的处理。 * 这非常类似于min_join_parameterization的transtivelyclosed lateral al_relid的计算， * 只是这里需要考虑添加的phv。 */ joinrel->direct_lateral_relids = bms_del_members(joinrel->direct_lateral_relids, joinrel->relids); if (bms_is_empty(joinrel->direct_lateral_relids)) joinrel->direct_lateral_relids = NULL; /* * Construct restrict and join clause lists for the new joinrel. (The * caller might or might not need the restrictlist, but I need it anyway * for set_joinrel_size_estimates().) * 为新产生的joinrel构造约束和连接条件链表 */ restrictlist = build_joinrel_restrictlist(root, joinrel, outer_rel, inner_rel);//构建限制条件链表 if (restrictlist_ptr) *restrictlist_ptr = restrictlist; build_joinrel_joinlist(joinrel, outer_rel, inner_rel);//构建连接条件链表 /* * This is also the right place to check whether the joinrel has any * pending EquivalenceClass joins. * 判断是否存在等价类EC */ joinrel->has_eclass_joins = has_relevant_eclass_joinclause(root, joinrel); /* S存储分区信息,tore the partition information. */ build_joinrel_partition_info(joinrel, outer_rel, inner_rel, restrictlist, sjinfo->jointype); /* * 估算joinrel的大小,Set estimates of the joinrel's size. */ set_joinrel_size_estimates(root, joinrel, outer_rel, inner_rel, sjinfo, restrictlist); /* * Set the consider_parallel flag if this joinrel could potentially be * scanned within a parallel worker. If this flag is false for either * inner_rel or outer_rel, then it must be false for the joinrel also. * Even if both are true, there might be parallel-restricted expressions * in the targetlist or quals. * 设置consider_parallel标记,如joinrel可以并行扫描的话 * * Note that if there are more than two rels in this relation, they could * be divided between inner_rel and outer_rel in any arbitrary way. We * assume this doesn't matter, because we should hit all the same baserels * and joinclauses while building up to this joinrel no matter which we * take; therefore, we should make the same decision here however we get * here. */ if (inner_rel->consider_parallel && outer_rel->consider_parallel && is_parallel_safe(root, (Node *) restrictlist) && is_parallel_safe(root, (Node *) joinrel->reltarget->exprs)) joinrel->consider_parallel = true; /* Add the joinrel to the PlannerInfo. */ add_join_rel(root, joinrel);//添加到优化器信息中 /* * Also, if dynamic-programming join search is active, add the new joinrel * to the appropriate sublist. Note: you might think the Assert on number * of members should be for equality, but some of the level 1 rels might * have been joinrels already, so we can only assert <=. * 添加到合适的链表中root->join_rel_levep[j] */ if (root->join_rel_level) { Assert(root->join_cur_level > 0); Assert(root->join_cur_level <= bms_num_members(joinrel->relids)); root->join_rel_level[root->join_cur_level] = lappend(root->join_rel_level[root->join_cur_level], joinrel);//加入到链表中 } return joinrel; }//----------------------------------------------- find_join_rel /* * find_join_rel * Returns relation entry corresponding to 'relids' (a set of RT indexes), * or NULL if none exists. This is for join relations. * 返回对应relids(RT indexes的集合)的RelOptInfo,如无则返回NULL. */ RelOptInfo * find_join_rel(PlannerInfo *root, Relids relids) { /* * Switch to using hash lookup when list grows "too long". The threshold * is arbitrary and is known only here. * 如链表过长,则改用hash查找 */ if (!root->join_rel_hash && list_length(root->join_rel_list) > 32) build_join_rel_hash(root); /* * Use either hashtable lookup or linear search, as appropriate. * 使用hash表查找或者线性搜索 * * Note: the seemingly redundant hashkey variable is used to avoid taking * the address of relids; unless the compiler is exceedingly smart, doing * so would force relids out of a register and thus probably slow down the * list-search case. */ if (root->join_rel_hash)//hash { Relids hashkey = relids; JoinHashEntry *hentry; hentry = (JoinHashEntry *) hash_search(root->join_rel_hash, &hashkey, HASH_FIND, NULL); if (hentry) return hentry->join_rel; } else//线性 { ListCell *l; foreach(l, root->join_rel_list) { RelOptInfo *rel = (RelOptInfo *) lfirst(l); if (bms_equal(rel->relids, relids)) return rel; } } return NULL; } //----------------------------------------------- build_joinrel_restrictlist /* * build_joinrel_restrictlist * build_joinrel_joinlist * These routines build lists of restriction and join clauses for a * join relation from the joininfo lists of the relations it joins. * 从关系的joininfo链表中建立限制条件和连接条件链表 * * These routines are separate because the restriction list must be * built afresh for each pair of input sub-relations we consider, whereas * the join list need only be computed once for any join RelOptInfo. * The join list is fully determined by the set of rels making up the * joinrel, so we should get the same results (up to ordering) from any * candidate pair of sub-relations. But the restriction list is whatever * is not handled in the sub-relations, so it depends on which * sub-relations are considered. * 这些处理过程是独立的，因为限制条件链表必须为所考虑的每一对输入子关系重新构建， * 而连接条件链表只需要为任何连接RelOptInfo计算一次即可。 * 连接链表完全由组成joinrel的一组rels决定， * 因此从任何子关系的候选对中都应该得到相同的结果(直到排序过程)。 * 但是限制条件链表是子关系中没有处理的内容，所以它取决于考虑的子关系。 * * If a join clause from an input relation refers to base rels still not * present in the joinrel, then it is still a join clause for the joinrel; * we put it into the joininfo list for the joinrel. Otherwise, * the clause is now a restrict clause for the joined relation, and we * return it to the caller of build_joinrel_restrictlist() to be stored in * join paths made from this pair of sub-relations. (It will not need to * be considered further up the join tree.) * 如果构成连接关系中的连接条件子句指向的base rels不在joinrel中, * 那么它仍然是joinrel的连接条件子句;这些信息会放到joinrel的joininfo链表中。 * 否则，如果条件子句现在是连接关系的限制子句， * 那么将它返回给build_joinrel_restrictlist()的调用方，将其存储在由这对子关系构成的连接路径中。 * (它不需要被认为位于连接树的更上层。) * * In many case we will find the same RestrictInfos in both input * relations' joinlists, so be careful to eliminate duplicates. * Pointer equality should be a sufficient test for dups, since all * the various joinlist entries ultimately refer to RestrictInfos * pushed into them by distribute_restrictinfo_to_rels(). * 在许多情况下，在两个关系的连接列表中可以发现相同的RestrictInfos，因此要小心排除重复。 * 指针相等的判断应该是对重复值的充分测试，因为所有的joinlist条目最终 * 都指向distribute_restrictinfo_to_rels()推入的RestrictInfos。 * * 'joinrel' is a join relation node,连接新产生的关系 * 'outer_rel' and 'inner_rel' are a pair of relations that can be joined * to form joinrel.连接的外表和内表 * * build_joinrel_restrictlist() returns a list of relevant restrictinfos, * whereas build_joinrel_joinlist() stores its results in the joinrel's * joininfo list. One or the other must accept each given clause! * build_joinrel_restrictlist()返回相关限制条件的链表, * 而build_joinrel_joinlist()把结果存储在joinrel的joininfo链表中 * * NB: Formerly, we made deep(!) copies of each input RestrictInfo to pass * up to the join relation. I believe this is no longer necessary, because * RestrictInfo nodes are no longer context-dependent. Instead, just include * the original nodes in the lists made for the join relation. */ static List * build_joinrel_restrictlist(PlannerInfo *root, RelOptInfo *joinrel, RelOptInfo *outer_rel, RelOptInfo *inner_rel) { List *result; /* * Collect all the clauses that syntactically belong at this level, * eliminating any duplicates (important since we will see many of the * same clauses arriving from both input relations). * 收集语法上属于该级别的所有限制条件子句，消除任何重复(这很重要，因为存在来自两个关系的相同子句)。 */ result = subbuild_joinrel_restrictlist(joinrel, outer_rel->joininfo, NIL); result = subbuild_joinrel_restrictlist(joinrel, inner_rel->joininfo, result); /* * Add on any clauses derived from EquivalenceClasses. These cannot be * redundant with the clauses in the joininfo lists, so don't bother * checking. * 添加来自EC的条件子句. */ result = list_concat(result, generate_join_implied_equalities(root, joinrel->relids, outer_rel->relids, inner_rel)); return result; } static void build_joinrel_joinlist(RelOptInfo *joinrel, RelOptInfo *outer_rel, RelOptInfo *inner_rel) { List *result; /* * Collect all the clauses that syntactically belong above this level, * eliminating any duplicates (important since we will see many of the * same clauses arriving from both input relations). * 收集语法上属于该级别的所有连接条件子句，消除任何重复(这很重要，因为存在来自两个关系的相同子句)。 */ result = subbuild_joinrel_joinlist(joinrel, outer_rel->joininfo, NIL); result = subbuild_joinrel_joinlist(joinrel, inner_rel->joininfo, result); joinrel->joininfo = result; } 测试表和数据继续沿用上一节创建的表和数据，使用的SQL语句如下:
testdb=# explain verbose select a.*,b.c1,c.c2,d.c2,e.c1,f.c2from a inner join b on a.c1=b.c1,c,d,e inner join f on e.c1 = f.c1 and e.c1 < 100where a.c1=f.c1 and b.c1=c.c1 and c.c1 = d.c1 and d.c1 = e.c1; QUERY PLAN ---------------------------------------------------------------------------------------------------------- Nested Loop (cost=101.17..2218.24 rows=2 width=42) Output: a.c1, a.c2, b.c1, c.c2, d.c2, e.c1, f.c2 Join Filter: (a.c1 = b.c1) -> Hash Join (cost=3.25..196.75 rows=100 width=22) Output: a.c1, a.c2, c.c2, c.c1 Hash Cond: (c.c1 = a.c1) -> Seq Scan on public.c (cost=0.00..155.00 rows=10000 width=12) Output: c.c1, c.c2 -> Hash (cost=2.00..2.00 rows=100 width=10) Output: a.c1, a.c2 -> Seq Scan on public.a (cost=0.00..2.00 rows=100 width=10) Output: a.c1, a.c2 -> Materialize (cost=97.92..2014.00 rows=5 width=32) Output: b.c1, d.c2, d.c1, e.c1, f.c2, f.c1 -> Hash Join (cost=97.92..2013.97 rows=5 width=32) Output: b.c1, d.c2, d.c1, e.c1, f.c2, f.c1 Hash Cond: (f.c1 = b.c1) -> Seq Scan on public.f (cost=0.00..1541.00 rows=100000 width=13) Output: f.c1, f.c2 -> Hash (cost=97.86..97.86 rows=5 width=19) Output: b.c1, d.c2, d.c1, e.c1 -> Hash Join (cost=78.10..97.86 rows=5 width=19) Output: b.c1, d.c2, d.c1, e.c1 Hash Cond: (b.c1 = e.c1) -> Seq Scan on public.b (cost=0.00..16.00 rows=1000 width=4) Output: b.c1, b.c2 -> Hash (cost=78.04..78.04 rows=5 width=15) Output: d.c2, d.c1, e.c1 -> Hash Join (cost=73.24..78.04 rows=5 width=15) Output: d.c2, d.c1, e.c1 Hash Cond: (d.c1 = e.c1) -> Seq Scan on public.d (cost=0.00..4.00 rows=200 width=11) Output: d.c1, d.c2 -> Hash (cost=72.00..72.00 rows=99 width=4) Output: e.c1 -> Seq Scan on public.e (cost=0.00..72.00 rows=99 width=4) Output: e.c1 Filter: (e.c1 < 100)(38 rows)
优化器选择了2 rels + 4 rels的连接模式,跟踪重点考察bushy plans的执行情况.
启动gdb,设置断点,只考察level=6的情况
(gdb) b join_search_one_levelBreakpoint 2 at 0x7b0289: file joinrels.c, line 67.(gdb) cContinuing....(gdb) cContinuing.Breakpoint 2, join_search_one_level (root=0x241ca38, level=6) at joinrels.c:6767 List **joinrels = root->join_rel_level;
完成5(rels)+1(rels)的调用
(gdb) b joinrels.c:142Breakpoint 3 at 0x7b03c4: file joinrels.c, line 142.(gdb) cContinuing.Breakpoint 3, join_search_one_level (root=0x241ca38, level=6) at joinrels.c:142142 for (k = 2;; k++)
查看root->join_rel_level[6]
(gdb) p *root->join_rel_level[6]$1 = {type = T_List, length = 1, head = 0x24c8468, tail = 0x24c8468} 查看该链表中的RelOptInfo
(gdb) set $roi=(RelOptInfo *)root->join_rel_level[6]->head->data.ptr_value(gdb) p *$roi$3 = {type = T_RelOptInfo, reloptkind = RELOPT_JOINREL, relids = 0x1eb8330, rows = 2, consider_startup = false, consider_param_startup = false, consider_parallel = true, reltarget = 0x1f25ac8, pathlist = 0x1f25f80, ppilist = 0x0, partial_pathlist = 0x0, cheapest_startup_path = 0x0, cheapest_total_path = 0x0, cheapest_unique_path = 0x0, cheapest_parameterized_paths = 0x0, direct_lateral_relids = 0x0, lateral_relids = 0x0, relid = 0, reltablespace = 0, rtekind = RTE_JOIN, min_attr = 0, max_attr = 0, attr_needed = 0x0, attr_widths = 0x0, lateral_vars = 0x0, lateral_referencers = 0x0, indexlist = 0x0, statlist = 0x0, pages = 0, tuples = 0, allvisfrac = 0, subroot = 0x0, subplan_params = 0x0, rel_parallel_workers = -1, serverid = 0, userid = 0, useridiscurrent = false, fdwroutine = 0x0, fdw_private = 0x0, unique_for_rels = 0x0, non_unique_for_rels = 0x0, baserestrictinfo = 0x0, baserestrictcost = { startup = 0, per_tuple = 0}, baserestrict_min_security = 4294967295, joininfo = 0x0, has_eclass_joins = false, top_parent_relids = 0x0, part_scheme = 0x0, nparts = 0, boundinfo = 0x0, partition_qual = 0x0, part_rels = 0x0, partexprs = 0x0, nullable_partexprs = 0x0, partitioned_child_rels = 0x0} 查看该RelOptInfo的pathlist
(gdb) p *$roi->pathlist$4 = {type = T_List, length = 1, head = 0x1f25f60, tail = 0x1f25f60}(gdb) p *(Node *)$roi->pathlist->head->data.ptr_value$5 = {type = T_NestPath}(gdb) set $np=(NestPath *)$roi->pathlist->head->data.ptr_value(gdb) p *(NestPath *)$np$5 = {path = {type = T_NestPath, pathtype = T_NestLoop, parent = 0x1f258b8, pathtarget = 0x1f25ac8, param_info = 0x0, parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 2, startup_cost = 290.57499999999999, total_cost = 2216.1374999999998, pathkeys = 0x0}, jointype = JOIN_INNER, inner_unique = false, outerjoinpath = 0x1f07c00, innerjoinpath = 0x1f27c40, joinrestrictinfo = 0x1f27e60} 查看该连接的外表和内部访问路径
(gdb) p *$np->outerjoinpath$6 = {type = T_Path, pathtype = T_SeqScan, parent = 0x1e228e8, pathtarget = 0x1f04bc0, param_info = 0x0, parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 100, startup_cost = 0, total_cost = 2, pathkeys = 0x0}(gdb) p *$np->innerjoinpath$7 = {type = T_MaterialPath, pathtype = T_Material, parent = 0x1ebb538, pathtarget = 0x1ebb748, param_info = 0x0, parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 5, startup_cost = 290.57499999999999, total_cost = 2206.6500000000001, pathkeys = 0x0} 下面开始尝试bushy plans,即（2/4 rels+ 4/2 rels)或(3 rels + 3 rels)模式,重点考察ac + bdef这种组合
(gdb) b joinrels.c:156Breakpoint 3 at 0x7557df: file joinrels.c, line 156.(gdb) cContinuing.Breakpoint 3, join_search_one_level (root=0x1e214b8, level=6) at joinrels.c:164164 if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins &&(gdb) p *old_rel->relids->words$13 = 18
进入make_join_rel函数
173 for_each_cell(r2, other_rels)(gdb) 175 RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);(gdb) 177 if (!bms_overlap(old_rel->relids, new_rel->relids))(gdb) 184 if (have_relevant_joinclause(root, old_rel, new_rel) ||(gdb) 187 (void) make_join_rel(root, old_rel, new_rel);(gdb) stepmake_join_rel (root=0x1e214b8, rel1=0x1f079f0, rel2=0x1e96520) at joinrels.c:681681 joinrelids = bms_union(rel1->relids, rel2->relids);
进入build_join_rel函数,相应的RelOptInfo已存在,返回
(gdb) 728 joinrel = build_join_rel(root, joinrelids, rel1, rel2, sjinfo,(gdb) stepbuild_join_rel (root=0x1e214b8, joinrelids=0x1e401d8, outer_rel=0x1f079f0, inner_rel=0x1e96520, sjinfo=0x7fff247e18a0, restrictlist_ptr=0x7fff247e1898) at relnode.c:498498 joinrel = find_join_rel(root, joinrelids);500 if (joinrel)(gdb) n506 if (restrictlist_ptr)(gdb) 507 *restrictlist_ptr = build_joinrel_restrictlist(root,(gdb) 511 return joinrel;
执行populate_joinrel_with_paths,该函数执行后再次查看外表和内部访问路径,变成了HashPath + MaterialPath的组合,具体的变化,下一节再行介绍.
...(gdb) 742 populate_joinrel_with_paths(root, rel1, rel2, joinrel, sjinfo,(gdb) n745 bms_free(joinrelids);(gdb) set $roi=(RelOptInfo *)root->join_rel_level[6]->head->data.ptr_value(gdb) set $np=(NestPath *)$roi->pathlist->head->data.ptr_value(gdb) p *$np->outerjoinpath$30 = {type = T_HashPath, pathtype = T_HashJoin, parent = 0x1f079f0, pathtarget = 0x1e41128, param_info = 0x0, parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 100, startup_cost = 3.25, total_cost = 196.75, pathkeys = 0x0}(gdb) p *$np->innerjoinpath$31 = {type = T_MaterialPath, pathtype = T_Material, parent = 0x1e96520, pathtarget = 0x1e96730, param_info = 0x0, parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 5, startup_cost = 97.962499999999991, total_cost = 2014.0375000000001, pathkeys = 0x0} DONE!
allpaths.c
cost.h costsize.c PG Document:Query Planning来自 “ ITPUB博客 ” ，链接：http://blog.itpub.net/6906/viewspace-2374836/，如需转载，请注明出处，否则将追究法律责任。
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