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PostgreSQL 源码解读(64)- 查询语句#49(mak

PostgreSQL 源码解读(64)- 查询语句#49(mak

作者: EthanHe | 来源:发表于2018-10-11 12:26 被阅读4次

    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。

    一、数据结构

    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;
    
    

    二、源码解读

    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;
     }
     
    

    三、跟踪分析

    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.c2
    from a inner join b on a.c1=b.c1,c,d,e inner join f on e.c1 = f.c1 and e.c1 < 100
    where 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_level
    Breakpoint 2 at 0x7b0289: file joinrels.c, line 67.
    (gdb) c
    Continuing.
    ...
    (gdb) c
    Continuing.
    
    Breakpoint 2, join_search_one_level (root=0x241ca38, level=6) at joinrels.c:67
    67      List      **joinrels = root->join_rel_level;
    

    完成5(rels)+1(rels)的调用

    (gdb) b joinrels.c:142
    Breakpoint 3 at 0x7b03c4: file joinrels.c, line 142.
    (gdb) c
    Continuing.
    
    Breakpoint 3, join_search_one_level (root=0x241ca38, level=6) at joinrels.c:142
    142     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:156
    Breakpoint 3 at 0x7557df: file joinrels.c, line 156.
    (gdb) c
    Continuing.
    
    Breakpoint 3, join_search_one_level (root=0x1e214b8, level=6) at joinrels.c:164
    164             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) step
    make_join_rel (root=0x1e214b8, rel1=0x1f079f0, rel2=0x1e96520) at joinrels.c:681
    681     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) step
    build_join_rel (root=0x1e214b8, joinrelids=0x1e401d8, outer_rel=0x1f079f0, inner_rel=0x1e96520, sjinfo=0x7fff247e18a0, 
        restrictlist_ptr=0x7fff247e1898) at relnode.c:498
    498     joinrel = find_join_rel(root, joinrelids);
    500     if (joinrel)
    (gdb) n
    506         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) n
    745     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!

    四、参考资料

    allpaths.c
    cost.h
    costsize.c
    PG Document:Query Planning

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