PostgreSQL中set_base_rel_sizes函数及其子函数案例分析

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make_one_rel源代码:

 RelOptInfo * make_one_rel(PlannerInfo *root, List *joinlist) {     RelOptInfo *rel;     Index       rti;      /*      * Construct the all_baserels Relids set.      */     root->all_baserels = NULL;     for (rti = 1; rti < root->simple_rel_array_size; rti++)//遍历RelOptInfo     {         RelOptInfo *brel = root->simple_rel_array[rti];          /* there may be empty slots corresponding to non-baserel RTEs */         if (brel == NULL)             continue;          Assert(brel->relid == rti); /* sanity check on array */          /* ignore RTEs that are "other rels" */         if (brel->reloptkind != RELOPT_BASEREL)             continue;          root->all_baserels = bms_add_member(root->all_baserels, brel->relid);//添加到all_baserels遍历中     }      /* Mark base rels as to whether we care about fast-start plans */     //设置RelOptInfo的consider_param_startup变量,是否考量fast-start plans     set_base_rel_consider_startup(root);      /*      * Compute size estimates and consider_parallel flags for each base rel,      * then generate access paths.      */     set_base_rel_sizes(root);//估算Relation的Size并且设置consider_parallel标记     set_base_rel_pathlists(root);//生成Relation的扫描(访问)路径      /*      * Generate access paths for the entire join tree.      * 通过动态规划或遗传算法生成连接路径       */     rel = make_rel_from_joinlist(root, joinlist);      /*      * The result should join all and only the query's base rels.      */     Assert(bms_equal(rel->relids, root->all_baserels));   //返回最上层的RelOptInfo     return rel; }

一、数据结构

RelOptInfo

 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

make_one_rel函数调用了set_base_rel_sizes,该函数的主要实现逻辑通过调用set_rel_size实现.现重点考察函数set_rel_size中对基础关系进行估算的处理逻辑,即函数set_plain_rel_size的实现逻辑.
set_plain_rel_size

 /*  * set_plain_rel_size  *    Set size estimates for a plain relation (no subquery, no inheritance)  */ static void set_plain_rel_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) {     /*      * Test any partial indexes of rel for applicability.  We must do this      * first since partial unique indexes can affect size estimates.      */     check_index_predicates(root, rel);//验证部分(条件)索引的可用性      /* Mark rel with estimated output rows, width, etc */     set_baserel_size_estimates(root, rel);//标记rel的输出行数/行宽等信息 }

set_plain_rel_size->check_index_predicates
如果部分(条件)索引的谓词与查询语句相匹配,则predOK设置为true
比如:
数据表t1(c1 int,c2 varchar(40),...),如存在索引idx_t1_partial_c1,条件为where c1 > 100
查询条件为where c1 > 100(是否支持>200?),那么该谓词与查询条件相匹配

//----------------------------------------- check_index_predicates /*  * check_index_predicates  *      Set the predicate-derived IndexOptInfo fields for each index  *      of the specified relation.  *  * predOK is set true if the index is partial and its predicate is satisfied  * for this query, ie the query's WHERE clauses imply the predicate.  * 如果部分(条件)索引的谓词与查询语句相匹配,则predOK设置为true  * 比如:  *    数据表t1(c1 int,c2 varchar(40),...),如存在索引idx_t1_partial_c1,条件为where c1 > 100  *    查询条件为where c1 > 100(是否支持>200?),那么该谓词与查询条件相匹配  *  * indrestrictinfo is set to the relation's baserestrictinfo list less any  * conditions that are implied by the index's predicate.  (Obviously, for a  * non-partial index, this is the same as baserestrictinfo.)  Such conditions  * can be dropped from the plan when using the index, in certain cases.  *   * indrestrictinfo会加入到rel的baserestrictinfo链表中,减少了索引谓词所隐含的限制条件.  *  * At one time it was possible for this to get re-run after adding more  * restrictions to the rel, thus possibly letting us prove more indexes OK.  * That doesn't happen any more (at least not in the core code's usage),  * but this code still supports it in case extensions want to mess with the  * baserestrictinfo list.  We assume that adding more restrictions can't make  * an index not predOK.  We must recompute indrestrictinfo each time, though,  * to make sure any newly-added restrictions get into it if needed.  */ void check_index_predicates(PlannerInfo *root, RelOptInfo *rel) {     List       *clauselist;//条件链表     bool        have_partial;//是否包含部分索引     bool        is_target_rel;//目标rel?     Relids      otherrels;//Relids     ListCell   *lc;//临时变量      /* Indexes are available only on base or "other" member relations. */     Assert(IS_SIMPLE_REL(rel));//rel必须是基础关系      /*      * Initialize the indrestrictinfo lists to be identical to      * baserestrictinfo, and check whether there are any partial indexes.  If      * not, this is all we need to do.      */     have_partial = false;     foreach(lc, rel->indexlist)//遍历index     {         IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);          index->indrestrictinfo = rel->baserestrictinfo;//设置索引约束条件         if (index->indpred)             have_partial = true;//存在部分索引     }     if (!have_partial)         return;      /*      * Construct a list of clauses that we can assume true for the purpose of      * proving the index(es) usable.  Restriction clauses for the rel are      * always usable, and so are any join clauses that are "movable to" this      * rel.  Also, we can consider any EC-derivable join clauses (which must      * be "movable to" this rel, by definition).      */     clauselist = list_copy(rel->baserestrictinfo);//条件语句初始化      /* Scan the rel's join clauses */     foreach(lc, rel->joininfo)//遍历连接条件     {         RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);//条件          /* Check if clause can be moved to this rel */         if (!join_clause_is_movable_to(rinfo, rel))//条件是否可以下推到Rel中             continue;//不可用,下一个条件          clauselist = lappend(clauselist, rinfo);//可以,则添加到条件语句链表中     }      /*      * Add on any equivalence-derivable join clauses.  Computing the correct      * relid sets for generate_join_implied_equalities is slightly tricky      * because the rel could be a child rel rather than a true baserel, and in      * that case we must remove its parents' relid(s) from all_baserels.      */     if (rel->reloptkind == RELOPT_OTHER_MEMBER_REL)         otherrels = bms_difference(root->all_baserels,                                    find_childrel_parents(root, rel));//     else         otherrels = bms_difference(root->all_baserels, rel->relids);//获取与rel无关的其他rels      if (!bms_is_empty(otherrels))         clauselist =             list_concat(clauselist,                         generate_join_implied_equalities(root,                                                          bms_union(rel->relids,                                                                    otherrels),                                                          otherrels,                                                          rel));//添加到条件语句      /*      * Normally we remove quals that are implied by a partial index's      * predicate from indrestrictinfo, indicating that they need not be      * checked explicitly by an indexscan plan using this index.  However, if      * the rel is a target relation of UPDATE/DELETE/SELECT FOR UPDATE, we      * cannot remove such quals from the plan, because they need to be in the      * plan so that they will be properly rechecked by EvalPlanQual testing.      * Some day we might want to remove such quals from the main plan anyway      * and pass them through to EvalPlanQual via a side channel; but for now,      * we just don't remove implied quals at all for target relations.      */     is_target_rel = (rel->relid == root->parse->resultRelation ||                      get_plan_rowmark(root->rowMarks, rel->relid) != NULL);      /*      * Now try to prove each index predicate true, and compute the      * indrestrictinfo lists for partial indexes.  Note that we compute the      * indrestrictinfo list even for non-predOK indexes; this might seem      * wasteful, but we may be able to use such indexes in OR clauses, cf      * generate_bitmap_or_paths().      */     foreach(lc, rel->indexlist)//遍历index     {         IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);         ListCell   *lcr;          if (index->indpred == NIL)             continue;           /* ignore non-partial indexes here */          if (!index->predOK)     /* don't repeat work if already proven OK */             index->predOK = predicate_implied_by(index->indpred, clauselist,                                                  false);//设置predOK参数          /* If rel is an update target, leave indrestrictinfo as set above */         if (is_target_rel)             continue;          /* Else compute indrestrictinfo as the non-implied quals */         index->indrestrictinfo = NIL;         foreach(lcr, rel->baserestrictinfo)         {             RestrictInfo *rinfo = (RestrictInfo *) lfirst(lcr);              /* predicate_implied_by() assumes first arg is immutable */             if (contain_mutable_functions((Node *) rinfo->clause) ||                 !predicate_implied_by(list_make1(rinfo->clause),                                       index->indpred, false))                 index->indrestrictinfo = lappend(index->indrestrictinfo, rinfo);//         }     } }

set_plain_rel_size->set_baserel_size_estimates
函数注释:

//----------------------------------------- set_baserel_size_estimates /*  * set_baserel_size_estimates  *      Set the size estimates for the given base relation.  *      估算base rel的估算大小  *  * The rel's targetlist and restrictinfo list must have been constructed  * already, and rel->tuples must be set.  *   rel的targetlist和限制条件链表已构建,并且tuples已获取.  *  * We set the following fields of the rel node:  * 通过该方法,设置以下3个变量  *  rows: the estimated number of output tuples (after applying  *        restriction clauses).  *        应用限制条件后,估算得出的输出元组数目  *  width: the estimated average output tuple width in bytes.  *        以字节为单位输出估算的平均元组大小  *  baserestrictcost: estimated cost of evaluating baserestrictinfo clauses.  *        解析限制条件的估算成本  */

源代码:

 void set_baserel_size_estimates(PlannerInfo *root, RelOptInfo *rel) {     double      nrows;      /* Should only be applied to base relations */     Assert(rel->relid > 0);      nrows = rel->tuples *         clauselist_selectivity(root,                                rel->baserestrictinfo,                                0,                                JOIN_INNER,                                NULL);//元组总数*选择率      rel->rows = clamp_row_est(nrows);      cost_qual_eval(&rel->baserestrictcost, rel->baserestrictinfo, root);      set_rel_width(root, rel); }//----------------------------------------- clauselist_selectivity /*  * clauselist_selectivity -  *    Compute the selectivity of an implicitly-ANDed list of boolean  *    expression clauses.  The list can be empty, in which case 1.0  *    must be returned.  List elements may be either RestrictInfos  *    or bare expression clauses --- the former is preferred since  *    it allows caching of results.  *  *    计算布尔表达式条件(隐式AND条件语句链表保存)的选择性.如果链表为空,  *    则返回1.0.链表中的元素可以是RestrictInfo结构体,也可以是裸条件表达式  *    (前者因为允许缓存,因此是首选)  *  * See clause_selectivity() for the meaning of the additional parameters.  *  * Our basic approach is to take the product of the selectivities of the  * subclauses.  However, that's only right if the subclauses have independent  * probabilities, and in reality they are often NOT independent.  So,  * we want to be smarter where we can.  *  * 采取的基本方法是subclauses的选择性乘积。采取这种做法的前台是子项具有独立的概率.  * 但实际上它们往往不是独立的,因此,需要在能做到的地方变得更好。   *  * If the clauses taken together refer to just one relation, we'll try to  * apply selectivity estimates using any extended statistics for that rel.  * Currently we only have (soft) functional dependencies, so apply these in as  * many cases as possible, and fall back on normal estimates for remaining  * clauses.  *  * 如果在一起的子句只涉及一个关系，将尝试应用关系上的扩展统计进行选择性的估算。  *  * We also recognize "range queries", such as "x > 34 AND x < 42".  Clauses  * are recognized as possible range query components if they are restriction  * opclauses whose operators have scalarltsel or a related function as their  * restriction selectivity estimator.  We pair up clauses of this form that  * refer to the same variable.  An unpairable clause of this kind is simply  * multiplied into the selectivity product in the normal way.  But when we  * find a pair, we know that the selectivities represent the relative  * positions of the low and high bounds within the column's range, so instead  * of figuring the selectivity as hisel * losel, we can figure it as hisel +  * losel - 1.  (To visualize this, see that hisel is the fraction of the range  * below the high bound, while losel is the fraction above the low bound; so  * hisel can be interpreted directly as a 0..1 value but we need to convert  * losel to 1-losel before interpreting it as a value.  Then the available  * range is 1-losel to hisel.  However, this calculation double-excludes  * nulls, so really we need hisel + losel + null_frac - 1.)  *  * 优化器还可以识别范围查询,比如x > 34 AND x < 42,这类范围查询不能简单的把x > 34  * 的选择率乘以x < 42的选择率,为方便起见,假定x < 42的选择率为hisel,x < 34的选择率为losel,  * 那么计算公式应该为hisel - (1 - losel),即hisel + losel -1,考虑NULL值,则范围查询的选择率  * 为hisel + losel + null_frac - 1  *  * If either selectivity is exactly DEFAULT_INEQ_SEL, we forget this equation  * and instead use DEFAULT_RANGE_INEQ_SEL.  The same applies if the equation  * yields an impossible (negative) result.  *  * 如果任意一个选择性都恰好是DEFAULT_INEQ_SEL，那么我们将忘记这个等式，  * 而使用DEFAULT_RANGE_INEQ_SEL。这种情况同样适用于如果等式产生了一个不可能的(负的)结果。  *  * A free side-effect is that we can recognize redundant inequalities such  * as "x < 4 AND x < 5"; only the tighter constraint will be counted.  *  * 我们可以识别冗余的不等式,比如x < 4 AND x <5,只有严格的约束条件才会计算在内  *  * Of course this is all very dependent on the behavior of the inequality  * selectivity functions; perhaps some day we can generalize the approach.  *   * 这完全取决于不等选择性函数的行为,也许有一天我们可以推广这种方法.  *  */ Selectivity clauselist_selectivity(PlannerInfo *root,                        List *clauses,                        int varRelid,                        JoinType jointype,                        SpecialJoinInfo *sjinfo) {     Selectivity s1 = 1.0;//默认返回值     RelOptInfo *rel;//     Bitmapset  *estimatedclauses = NULL;//位图集合     RangeQueryClause *rqlist = NULL;//范围查询语句     ListCell   *l;//临时变量     int         listidx;      /*      * If there's exactly one clause, just go directly to      * clause_selectivity(). None of what we might do below is relevant.      */     if (list_length(clauses) == 1)         return clause_selectivity(root, (Node *) linitial(clauses),                                   varRelid, jointype, sjinfo);//单个条件      /*      * Determine if these clauses reference a single relation.  If so, and if      * it has extended statistics, try to apply those.      */     //如果条件链表中的元素依赖的rel有且只有一个,则返回此rel     rel = find_single_rel_for_clauses(root, clauses);     //应用dependencies_clauselist_selectivity中的可用的条件进行选择率估算     if (rel && rel->rtekind == RTE_RELATION && rel->statlist != NIL)     {         /*          * Perform selectivity estimations on any clauses found applicable by          * dependencies_clauselist_selectivity.  'estimatedclauses' will be          * filled with the 0-based list positions of clauses used that way, so          * that we can ignore them below.          */         s1 *= dependencies_clauselist_selectivity(root, clauses, varRelid,                                                   jointype, sjinfo, rel,                                                   &estimatedclauses);          /*          * This would be the place to apply any other types of extended          * statistics selectivity estimations for remaining clauses.          */     }      /*      * Apply normal selectivity estimates for remaining clauses. We'll be      * careful to skip any clauses which were already estimated above.      * 剩下的条件语句,应用常规的选择率估算.      *      * Anything that doesn't look like a potential rangequery clause gets      * multiplied into s1 and forgotten. Anything that does gets inserted into      * an rqlist entry.      * 非范围条件语句乘上s1后被丢弃,范围条件语句则加入到rqlist链表中.      */     listidx = -1;     foreach(l, clauses)//遍历     {         Node       *clause = (Node *) lfirst(l);//链表中的元素         RestrictInfo *rinfo;         Selectivity s2;          listidx++;          /*          * Skip this clause if it's already been estimated by some other          * statistics above.          */         if (bms_is_member(listidx, estimatedclauses))//跳过已处理的条件             continue;          /* Always compute the selectivity using clause_selectivity */         s2 = clause_selectivity(root, clause, varRelid, jointype, sjinfo);//获取条件选择率          /*          * Check for being passed a RestrictInfo.          *          * If it's a pseudoconstant RestrictInfo, then s2 is either 1.0 or          * 0.0; just use that rather than looking for range pairs.          */         if (IsA(clause, RestrictInfo))//条件语句是RestrictInfo类型         {             rinfo = (RestrictInfo *) clause;             if (rinfo->pseudoconstant)//常量             {                 s1 = s1 * s2;//直接相乘                 continue;             }             clause = (Node *) rinfo->clause;//条件表达式         }         else             rinfo = NULL;//不是RestrictInfo类型,rinfo设置为NULL          /*          * See if it looks like a restriction clause with a pseudoconstant on          * one side.  (Anything more complicated than that might not behave in          * the simple way we are expecting.)  Most of the tests here can be          * done more efficiently with rinfo than without.          */         if (is_opclause(clause) && list_length(((OpExpr *) clause)->args) == 2)//OpExpr         {             OpExpr     *expr = (OpExpr *) clause;//条件语句             bool        varonleft = true;             bool        ok;              if (rinfo)//rinfo中的条件语句             {                 ok = (bms_membership(rinfo->clause_relids) == BMS_SINGLETON) &&                     (is_pseudo_constant_clause_relids(lsecond(expr->args),                                                       rinfo->right_relids) ||                      (varonleft = false,                       is_pseudo_constant_clause_relids(linitial(expr->args),                                                        rinfo->left_relids)));             }             else//裸条件语句             {                 ok = (NumRelids(clause) == 1) &&                     (is_pseudo_constant_clause(lsecond(expr->args)) ||                      (varonleft = false,                       is_pseudo_constant_clause(linitial(expr->args))));             }              if (ok)//校验通过             {                 /*                  * If it's not a "<"/"<="/">"/">=" operator, just merge the                  * selectivity in generically.  But if it's the right oprrest,                  * add the clause to rqlist for later processing.                  */                 switch (get_oprrest(expr->opno))                 {                     case F_SCALARLTSEL:                     case F_SCALARLESEL:                         addRangeClause(&rqlist, clause,                                        varonleft, true, s2);//范围条件                         break;                     case F_SCALARGTSEL:                     case F_SCALARGESEL:                         addRangeClause(&rqlist, clause,                                        varonleft, false, s2);//范围条件                         break;                     default:                         /* Just merge the selectivity in generically */                         s1 = s1 * s2;//直接相乘                         break;                 }                 continue;       /* drop to loop bottom */             }         }          /* Not the right form, so treat it generically. */         s1 = s1 * s2;//直接相乘     }      /*      * Now scan the rangequery pair list.      */     while (rqlist != NULL)//处理范围条件     {         RangeQueryClause *rqnext;          if (rqlist->have_lobound && rqlist->have_hibound)//存在上下限         {             /* Successfully matched a pair of range clauses */             Selectivity s2;//选择率              /*              * Exact equality to the default value probably means the              * selectivity function punted.  This is not airtight but should              * be good enough.              */             if (rqlist->hibound == DEFAULT_INEQ_SEL ||                 rqlist->lobound == DEFAULT_INEQ_SEL)//默认值             {                 s2 = DEFAULT_RANGE_INEQ_SEL;//默认为DEFAULT_RANGE_INEQ_SEL             }             else             {                 s2 = rqlist->hibound + rqlist->lobound - 1.0;//计算公式在注释已解释                  /* Adjust for double-exclusion of NULLs */                 s2 += nulltestsel(root, IS_NULL, rqlist->var,                                   varRelid, jointype, sjinfo);//NULL值                  /*                  * A zero or slightly negative s2 should be converted into a                  * small positive value; we probably are dealing with a very                  * tight range and got a bogus result due to roundoff errors.                  * However, if s2 is very negative, then we probably have                  * default selectivity estimates on one or both sides of the                  * range that we failed to recognize above for some reason.                  */                 if (s2 <= 0.0)//小于0?                 {                     if (s2 < -0.01)                     {                         /*                          * No data available --- use a default estimate that                          * is small, but not real small.                          */                         s2 = DEFAULT_RANGE_INEQ_SEL;//小于﹣1%,默认值                     }                     else                     {                         /*                          * It's just roundoff error; use a small positive                          * value                          */                         s2 = 1.0e-10;,//否则设置为1的﹣10次方                     }                 }             }             /* Merge in the selectivity of the pair of clauses */             s1 *= s2;//直接相乘         }         else//只有其中一个限制         {             /* Only found one of a pair, merge it in generically */             if (rqlist->have_lobound)                 s1 *= rqlist->lobound;//下限             else                 s1 *= rqlist->hibound;//上限         }         /* release storage and advance */         rqnext = rqlist->next;//释放资源         pfree(rqlist);         rqlist = rqnext;     }      return s1;//返回选择率 } /*  * clause_selectivity -  *    Compute the selectivity of a general boolean expression clause.  *    计算布尔表达式条件语句的选择率  *  * The clause can be either a RestrictInfo or a plain expression.  If it's  * a RestrictInfo, we try to cache the selectivity for possible re-use,  * so passing RestrictInfos is preferred.  *   clause可以是RestrictInfo结构体或者是常规的表达式.如果是RestrictInfo,  *   那么我们会尝试缓存结果已便于重用.  *  * varRelid is either 0 or a rangetable index.  *    varRelid是0或者是RTE编号  *  * When varRelid is not 0, only variables belonging to that relation are  * considered in computing selectivity; other vars are treated as constants  * of unknown values.  This is appropriate for estimating the selectivity of  * a join clause that is being used as a restriction clause in a scan of a  * nestloop join's inner relation --- varRelid should then be the ID of the  * inner relation.  *    如果varRelid不为0,只有属于该Rel的变量才会考虑计算选择率,其他变量作为未知常量处理  *    这种情况常见于嵌套循环内表的选择率估算(varRelid是内部的RTE)  *  * When varRelid is 0, all variables are treated as variables.  This  * is appropriate for ordinary join clauses and restriction clauses.  *    如果varRelid为0,所有的变量都需要考虑,用于常规的连接条件和限制条件估算  *  *  * jointype is the join type, if the clause is a join clause.  Pass JOIN_INNER  * if the clause isn't a join clause.  *    如果条件是连接条件,那么jointype是连接类型,如果不是连接调整,则该参数为JOIN_INNER  *  * sjinfo is NULL for a non-join clause, otherwise it provides additional  * context information about the join being performed.  There are some  * special cases:  *  1. For a special (not INNER) join, sjinfo is always a member of  *     root->join_info_list.非INNER_JOIN,sjinfo通常是oot->join_info_list的一个元素  *  2. For an INNER join, sjinfo is just a transient struct, and only the  *     relids and jointype fields in it can be trusted.INNER_JOIN,sjinfo通常是临时的结构  * It is possible for jointype to be different from sjinfo->jointype.//jointype可能跟sjinfo中的jointype不同  * This indicates we are considering a variant join: either with  * the LHS and RHS switched, or with one input unique-ified.这意味着连接有可能会变换  *  * Note: when passing nonzero varRelid, it's normally appropriate to set  * jointype == JOIN_INNER, sjinfo == NULL, even if the clause is really a  * join clause; because we aren't treating it as a join clause.  */ Selectivity clause_selectivity(PlannerInfo *root,                    Node *clause,                    int varRelid,                    JoinType jointype,                    SpecialJoinInfo *sjinfo) {     Selectivity s1 = 0.5;       /* 默认值,default for any unhandled clause type */     RestrictInfo *rinfo = NULL;     bool        cacheable = false;      if (clause == NULL)         /* can this still happen? */         return s1;      if (IsA(clause, RestrictInfo))//RestrictInfo     {         rinfo = (RestrictInfo *) clause;          /*          * If the clause is marked pseudoconstant, then it will be used as a          * gating qual and should not affect selectivity estimates; hence          * return 1.0.  The only exception is that a constant FALSE may be          * taken as having selectivity 0.0, since it will surely mean no rows          * out of the plan.  This case is simple enough that we need not          * bother caching the result.          */         if (rinfo->pseudoconstant)//pseudoconstant,不影响选择率         {             if (!IsA(rinfo->clause, Const))                 return (Selectivity) 1.0;//返回1.0         }          /*          * If the clause is marked redundant, always return 1.0.          */         if (rinfo->norm_selec > 1)             return (Selectivity) 1.0;//返回1.0          /*          * If possible, cache the result of the selectivity calculation for          * the clause.  We can cache if varRelid is zero or the clause          * contains only vars of that relid --- otherwise varRelid will affect          * the result, so mustn't cache.  Outer join quals might be examined          * with either their join's actual jointype or JOIN_INNER, so we need          * two cache variables to remember both cases.  Note: we assume the          * result won't change if we are switching the input relations or          * considering a unique-ified case, so we only need one cache variable          * for all non-JOIN_INNER cases.          */         if (varRelid == 0 ||             bms_is_subset_singleton(rinfo->clause_relids, varRelid))//varRelid为0         {             /* Cacheable --- do we already have the result? */             if (jointype == JOIN_INNER)             {                 if (rinfo->norm_selec >= 0)                     return rinfo->norm_selec;             }             else             {                 if (rinfo->outer_selec >= 0)                     return rinfo->outer_selec;             }             cacheable = true;         }          /*          * Proceed with examination of contained clause.  If the clause is an          * OR-clause, we want to look at the variant with sub-RestrictInfos,          * so that per-subclause selectivities can be cached.          */         if (rinfo->orclause)             clause = (Node *) rinfo->orclause;         else             clause = (Node *) rinfo->clause;     }      if (IsA(clause, Var))//Var     {         Var        *var = (Var *) clause;          /*          * We probably shouldn't ever see an uplevel Var here, but if we do,          * return the default selectivity...          */         if (var->varlevelsup == 0 &&             (varRelid == 0 || varRelid == (int) var->varno))         {             /* Use the restriction selectivity function for a bool Var */             s1 = boolvarsel(root, (Node *) var, varRelid);//bool Var选择率         }     }     else if (IsA(clause, Const))//常量     {         /* bool constant is pretty easy... */         Const      *con = (Const *) clause;          s1 = con->constisnull ? 0.0 :             DatumGetBool(con->constvalue) ? 1.0 : 0.0;//常量有效则为1.0,否则为0.0     }     else if (IsA(clause, Param))//参数     {         /* see if we can replace the Param */         Node       *subst = estimate_expression_value(root, clause);          if (IsA(subst, Const))         {             /* bool constant is pretty easy... */             Const      *con = (Const *) subst;              s1 = con->constisnull ? 0.0 :                 DatumGetBool(con->constvalue) ? 1.0 : 0.0;         }         else         {             /* XXX any way to do better than default? */         }     }     else if (not_clause(clause))//反选     {         /* inverse of the selectivity of the underlying clause */         s1 = 1.0 - clause_selectivity(root,                                       (Node *) get_notclausearg((Expr *) clause),                                       varRelid,                                       jointype,                                       sjinfo);     }     else if (and_clause(clause))//AND语句     {         /* share code with clauselist_selectivity() */         s1 = clauselist_selectivity(root,                                     ((BoolExpr *) clause)->args,                                     varRelid,                                     jointype,                                     sjinfo);//递归调用     }     else if (or_clause(clause))//OR语句     {         /*          * Selectivities for an OR clause are computed as s1+s2 - s1*s2 to          * account for the probable overlap of selected tuple sets.          *          * XXX is this too conservative?          */         ListCell   *arg;          s1 = 0.0;         foreach(arg, ((BoolExpr *) clause)->args)         {             Selectivity s2 = clause_selectivity(root,                                                 (Node *) lfirst(arg),                                                 varRelid,                                                 jointype,                                                 sjinfo);//递归调用              s1 = s1 + s2 - s1 * s2;         }     }     else if (is_opclause(clause) || IsA(clause, DistinctExpr))     {         OpExpr     *opclause = (OpExpr *) clause;         Oid         opno = opclause->opno;          if (treat_as_join_clause(clause, rinfo, varRelid, sjinfo))         {             /* Estimate selectivity for a join clause. */             s1 = join_selectivity(root, opno,                                   opclause->args,                                   opclause->inputcollid,                                   jointype,                                   sjinfo);//连接条件         }         else         {             /* Estimate selectivity for a restriction clause. */             s1 = restriction_selectivity(root, opno,                                          opclause->args,                                          opclause->inputcollid,                                          varRelid);//限制条件         }          /*          * DistinctExpr has the same representation as OpExpr, but the          * contained operator is "=" not "<>", so we must negate the result.          * This estimation method doesn't give the right behavior for nulls,          * but it's better than doing nothing.          */         if (IsA(clause, DistinctExpr))             s1 = 1.0 - s1;//Distinct?     }     else if (IsA(clause, ScalarArrayOpExpr))//数组     {         /* Use node specific selectivity calculation function */         s1 = scalararraysel(root,                             (ScalarArrayOpExpr *) clause,                             treat_as_join_clause(clause, rinfo,                                                  varRelid, sjinfo),                             varRelid,                             jointype,                             sjinfo);     }     else if (IsA(clause, RowCompareExpr))//行对比     {         /* Use node specific selectivity calculation function */         s1 = rowcomparesel(root,                            (RowCompareExpr *) clause,                            varRelid,                            jointype,                            sjinfo);     }     else if (IsA(clause, NullTest))//NullTest     {         /* Use node specific selectivity calculation function */         s1 = nulltestsel(root,                          ((NullTest *) clause)->nulltesttype,                          (Node *) ((NullTest *) clause)->arg,                          varRelid,                          jointype,                          sjinfo);     }     else if (IsA(clause, BooleanTest))//BooleanTest     {         /* Use node specific selectivity calculation function */         s1 = booltestsel(root,                          ((BooleanTest *) clause)->booltesttype,                          (Node *) ((BooleanTest *) clause)->arg,                          varRelid,                          jointype,                          sjinfo);     }     else if (IsA(clause, CurrentOfExpr))//CurrentOfExpr     {         /* CURRENT OF selects at most one row of its table */         CurrentOfExpr *cexpr = (CurrentOfExpr *) clause;         RelOptInfo *crel = find_base_rel(root, cexpr->cvarno);          if (crel->tuples > 0)             s1 = 1.0 / crel->tuples;     }     else if (IsA(clause, RelabelType))//RelabelType     {         /* Not sure this case is needed, but it can't hurt */         s1 = clause_selectivity(root,                                 (Node *) ((RelabelType *) clause)->arg,                                 varRelid,                                 jointype,                                 sjinfo);     }     else if (IsA(clause, CoerceToDomain))//CoerceToDomain     {         /* Not sure this case is needed, but it can't hurt */         s1 = clause_selectivity(root,                                 (Node *) ((CoerceToDomain *) clause)->arg,                                 varRelid,                                 jointype,                                 sjinfo);     }     else     {         /*          * For anything else, see if we can consider it as a boolean variable.          * This only works if it's an immutable expression in Vars of a single          * relation; but there's no point in us checking that here because          * boolvarsel() will do it internally, and return a suitable default          * selectivity if not.          */         s1 = boolvarsel(root, clause, varRelid);//默认为bool Var     }      /* Cache the result if possible */     if (cacheable)//缓存?     {         if (jointype == JOIN_INNER)             rinfo->norm_selec = s1;         else             rinfo->outer_selec = s1;     }  #ifdef SELECTIVITY_DEBUG     elog(DEBUG4, "clause_selectivity: s1 %f", s1); #endif                          /* SELECTIVITY_DEBUG */      return s1; } /*  * find_single_rel_for_clauses  *      Examine each clause in 'clauses' and determine if all clauses  *      reference only a single relation.  If so return that relation,  *      otherwise return NULL.  *  *      如果条件链表中的元素依赖的rel有且只有一个,则返回此rel  */ static RelOptInfo * find_single_rel_for_clauses(PlannerInfo *root, List *clauses) {     int         lastrelid = 0;     ListCell   *l;      foreach(l, clauses)     {         RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);         int         relid;          /*          * If we have a list of bare clauses rather than RestrictInfos, we          * could pull out their relids the hard way with pull_varnos().          * However, currently the extended-stats machinery won't do anything          * with non-RestrictInfo clauses anyway, so there's no point in          * spending extra cycles; just fail if that's what we have.          */         if (!IsA(rinfo, RestrictInfo))             return NULL;          if (bms_is_empty(rinfo->clause_relids))             continue;           /* we can ignore variable-free clauses */         if (!bms_get_singleton_member(rinfo->clause_relids, &relid))             return NULL;        /* multiple relations in this clause */         if (lastrelid == 0)             lastrelid = relid;  /* first clause referencing a relation */         else if (relid != lastrelid)             return NULL;        /* relation not same as last one */     }      if (lastrelid != 0)         return find_base_rel(root, lastrelid);      return NULL;                /* no clauses */ }//---------------------------------------------- clamp_row_est /*  * clamp_row_est  *      Force a row-count estimate to a sane value.  *      返回合法值  */ double clamp_row_est(double nrows) {     /*      * Force estimate to be at least one row, to make explain output look      * better and to avoid possible divide-by-zero when interpolating costs.      * Make it an integer, too.      */     if (nrows <= 1.0)         nrows = 1.0;//小于1,返回1     else         nrows = rint(nrows);//整型      return nrows; } //---------------------------------------------- cost_qual_eval /*  * cost_qual_eval  *      Estimate the CPU costs of evaluating a WHERE clause.  *      The input can be either an implicitly-ANDed list of boolean  *      expressions, or a list of RestrictInfo nodes.  (The latter is  *      preferred since it allows caching of the results.)  *      The result includes both a one-time (startup) component,  *      and a per-evaluation component.  */ void cost_qual_eval(QualCost *cost, List *quals, PlannerInfo *root) {     cost_qual_eval_context context;     ListCell   *l;      context.root = root;     context.total.startup = 0;     context.total.per_tuple = 0;      /* We don't charge any cost for the implicit ANDing at top level ... */      foreach(l, quals)     {         Node       *qual = (Node *) lfirst(l);          cost_qual_eval_walker(qual, &context);     }      *cost = context.total; }//---------------------------------------------- set_rel_width /*  * set_rel_width  *      Set the estimated output width of a base relation.  *  * The estimated output width is the sum of the per-attribute width estimates  * for the actually-referenced columns, plus any PHVs or other expressions  * that have to be calculated at this relation.  This is the amount of data  * we'd need to pass upwards in case of a sort, hash, etc.  *  * This function also sets reltarget->cost, so it's a bit misnamed now.  *  * NB: this works best on plain relations because it prefers to look at  * real Vars.  For subqueries, set_subquery_size_estimates will already have  * copied up whatever per-column estimates were made within the subquery,  * and for other types of rels there isn't much we can do anyway.  We fall  * back on (fairly stupid) datatype-based width estimates if we can't get  * any better number.  *  * The per-attribute width estimates are cached for possible re-use while  * building join relations or post-scan/join pathtargets.  */ static void set_rel_width(PlannerInfo *root, RelOptInfo *rel) {     Oid         reloid = planner_rt_fetch(rel->relid, root)->relid;     int32       tuple_width = 0;     bool        have_wholerow_var = false;     ListCell   *lc;      /* Vars are assumed to have cost zero, but other exprs do not */     rel->reltarget->cost.startup = 0;     rel->reltarget->cost.per_tuple = 0;      foreach(lc, rel->reltarget->exprs)     {         Node       *node = (Node *) lfirst(lc);          /*          * Ordinarily, a Var in a rel's targetlist must belong to that rel;          * but there are corner cases involving LATERAL references where that          * isn't so.  If the Var has the wrong varno, fall through to the          * generic case (it doesn't seem worth the trouble to be any smarter).          */         if (IsA(node, Var) &&             ((Var *) node)->varno == rel->relid)         {             Var        *var = (Var *) node;             int         ndx;             int32       item_width;              Assert(var->varattno >= rel->min_attr);             Assert(var->varattno <= rel->max_attr);              ndx = var->varattno - rel->min_attr;              /*              * If it's a whole-row Var, we'll deal with it below after we have              * already cached as many attr widths as possible.              */             if (var->varattno == 0)             {                 have_wholerow_var = true;                 continue;             }              /*              * The width may have been cached already (especially if it's a              * subquery), so don't duplicate effort.              */             if (rel->attr_widths[ndx] > 0)             {                 tuple_width += rel->attr_widths[ndx];                 continue;             }              /* Try to get column width from statistics */             if (reloid != InvalidOid && var->varattno > 0)             {                 item_width = get_attavgwidth(reloid, var->varattno);                 if (item_width > 0)                 {                     rel->attr_widths[ndx] = item_width;                     tuple_width += item_width;                     continue;                 }             }              /*              * Not a plain relation, or can't find statistics for it. Estimate              * using just the type info.              */             item_width = get_typavgwidth(var->vartype, var->vartypmod);             Assert(item_width > 0);             rel->attr_widths[ndx] = item_width;             tuple_width += item_width;         }         else if (IsA(node, PlaceHolderVar))         {             /*              * We will need to evaluate the PHV's contained expression while              * scanning this rel, so be sure to include it in reltarget->cost.              */             PlaceHolderVar *phv = (PlaceHolderVar *) node;             PlaceHolderInfo *phinfo = find_placeholder_info(root, phv, false);             QualCost    cost;              tuple_width += phinfo->ph_width;             cost_qual_eval_node(&cost, (Node *) phv->phexpr, root);             rel->reltarget->cost.startup += cost.startup;             rel->reltarget->cost.per_tuple += cost.per_tuple;         }         else         {             /*              * We could be looking at an expression pulled up from a subquery,              * or a ROW() representing a whole-row child Var, etc.  Do what we              * can using the expression type information.              */             int32       item_width;             QualCost    cost;              item_width = get_typavgwidth(exprType(node), exprTypmod(node));             Assert(item_width > 0);             tuple_width += item_width;             /* Not entirely clear if we need to account for cost, but do so */             cost_qual_eval_node(&cost, node, root);             rel->reltarget->cost.startup += cost.startup;             rel->reltarget->cost.per_tuple += cost.per_tuple;         }     }      /*      * If we have a whole-row reference, estimate its width as the sum of      * per-column widths plus heap tuple header overhead.      */     if (have_wholerow_var)     {         int32       wholerow_width = MAXALIGN(SizeofHeapTupleHeader);          if (reloid != InvalidOid)         {             /* Real relation, so estimate true tuple width */             wholerow_width += get_relation_data_width(reloid,                                                       rel->attr_widths - rel->min_attr);         }         else         {             /* Do what we can with info for a phony rel */             AttrNumber  i;              for (i = 1; i <= rel->max_attr; i++)                 wholerow_width += rel->attr_widths[i - rel->min_attr];         }          rel->attr_widths[0 - rel->min_attr] = wholerow_width;          /*          * Include the whole-row Var as part of the output tuple.  Yes, that          * really is what happens at runtime.          */         tuple_width += wholerow_width;     }      Assert(tuple_width >= 0);     rel->reltarget->width = tuple_width; }

三、跟踪分析

测试脚本:
单位信息表,插入100,000行数据,dwbh为主键,同时创建函数索引和部分索引

drop table if exists t_dwxx;create table t_dwxx(dwmc varchar(100),dwbh varchar(20),dwdz varchar(100));alter table t_dwxx add primary key(dwbh);create index idx_dwxx_expr on t_dwxx(trim(dwmc));create index idx_dwxx_predicate_dwbh on t_dwxx(dwbh) where dwbh > '50000';truncate table t_dwxx;insert into t_dwxx(dwmc,dwbh,dwdz) select 'DWMC'||generate_series(1,100000),generate_series(1,100000)||'','DWDZ'||generate_series(1,100000);

个人信息表,插入5,000,000行数据,在grbh和dwbh上创建索引

drop table if exists t_grxx;create table t_grxx(dwbh varchar(10),grbh varchar(10),xm varchar(20),xb varchar(10),nl int);insert into t_grxx(dwbh,grbh,xm,xb,nl) select generate_series(1,5000000)/50||'',generate_series(1,5000000),'XM'||generate_series(1,5000000),(case when (floor(random()*2)=0) then '男' else '女' end),floor(random() * 100 + 1)::int;create index idx_t_grxx_grbh on t_grxx(grbh);create index idx_t_dwxx_grbh on t_grxx(dwbh);

个人缴费信息表,在grbh上创建索引,多次插入5,000,000行数据

drop table if exists t_jfxx;create table t_jfxx(grbh varchar(10),ny varchar(10),je float);-- 根据实际情况,多次执行以下SQLinsert into t_jfxx(grbh,ny,je) select generate_series(1,5000000),       to_char(now()::timestamp - (floor(random()*240+1)||' month')::interval,'yyyymm'),       floor(random()*10000+1);create index idx_t_jfxx_grbh on t_jfxx(grbh);

执行简单的查询SQL:

select t1.* from t_dwxx t1 where dwbh > '60000' and dwbh < '70000' and dwbh < '65000';

执行计划如下:

testdb=# explain (analyze true,verbose) select t1.* from t_dwxx t1 where dwbh > '60000' and dwbh < '70000' and dwbh < '65000';                                                               QUERY PLAN                                                               ---------------------------------------------------------------------------------------------------------------------------------------- Bitmap Heap Scan on public.t_dwxx t1  (cost=134.19..956.12 rows=5482 width=23) (actual time=1.484..2.744 rows=5554 loops=1)   Output: dwmc, dwbh, dwdz   Recheck Cond: (((t1.dwbh)::text > '60000'::text) AND ((t1.dwbh)::text < '70000'::text) AND ((t1.dwbh)::text < '65000'::text))   Heap Blocks: exact=45   ->  Bitmap Index Scan on idx_dwxx_predicate_dwbh  (cost=0.00..132.81 rows=5482 width=0) (actual time=1.467..1.467 rows=5554 loops=1)         Index Cond: (((t1.dwbh)::text > '60000'::text) AND ((t1.dwbh)::text < '70000'::text) AND ((t1.dwbh)::text < '65000'::text)) Planning Time: 0.204 ms Execution Time: 3.288 ms

启动gdb跟踪分析:

(gdb) b set_baserel_size_estimatesBreakpoint 1 at 0x747bf5: file costsize.c, line 4302.(gdb) cContinuing.Breakpoint 1, set_baserel_size_estimates (root=0x2686fa8, rel=0x26873b8) at costsize.c:43024302    nrows = rel->tuples *

进入函数clauselist_selectivity:

(gdb) stepclauselist_selectivity (root=0x2686fa8, clauses=0x271f600, varRelid=0, jointype=JOIN_INNER, sjinfo=0x0) at clausesel.c:105105   Selectivity s1 = 1.0;...124   rel = find_single_rel_for_clauses(root, clauses);(gdb) 125   if (rel && rel->rtekind == RTE_RELATION && rel->statlist != NIL)#与限制条件相关的rel(t_dwxx)(gdb) p *rel$1 = {type = T_RelOptInfo, reloptkind = RELOPT_BASEREL, relids = 0x2687728, rows = 0, consider_startup = false,   consider_param_startup = false, consider_parallel = true, reltarget = 0x271e228, pathlist = 0x0, 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 = 1, reltablespace = 0,   rtekind = RTE_RELATION, min_attr = -7, max_attr = 3, attr_needed = 0x271e278, attr_widths = 0x271e308,   lateral_vars = 0x0, lateral_referencers = 0x0, indexlist = 0x271e700, statlist = 0x0, pages = 726, tuples = 100000,   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 = 0x271f600, baserestrictcost = {startup = 0, per_tuple = 0}, baserestrict_min_security = 0,   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}

开始循环处理:

152   foreach(l, clauses)...

第一个条件语句,调用clause_selectivity后,选择率为0.44...

168     s2 = clause_selectivity(root, clause, varRelid, jointype, sjinfo);(gdb) 176     if (IsA(clause, RestrictInfo))(gdb) p s2$2 = 0.44045086705202319

添加到范围条件语句中:

...225         switch (get_oprrest(expr->opno))(gdb) 234             addRangeClause(&rqlist, clause,(gdb) 236             break;

第二个条件语句,调用clause_selectivity后,选择率为0.66...,,同样会添加到范围条件语句中:

168     s2 = clause_selectivity(root, clause, varRelid, jointype, sjinfo);(gdb) 176     if (IsA(clause, RestrictInfo))(gdb) p s2$3 = 0.66904390539053915...225         switch (get_oprrest(expr->opno))(gdb) 229             addRangeClause(&rqlist, clause,

第三个条件语句,调用clause_selectivity后,选择率为0.61...,,同样会添加到范围条件语句中:

168     s2 = clause_selectivity(root, clause, varRelid, jointype, sjinfo);(gdb) 176     if (IsA(clause, RestrictInfo))(gdb) p s2$4 = 0.61437297872340435...225         switch (get_oprrest(expr->opno))(gdb) 229             addRangeClause(&rqlist, clause,

结束循环,开始处理范围条件语句:

253   while (rqlist != NULL)(gdb) n#既有上限,也有下限(gdb) p *rqlist$7 = {next = 0x0, var = 0x271dba8, have_lobound = true, have_hibound = true, lobound = 0.44045086705202319,   hibound = 0.61437297872340435}...#计算公式注释已作介绍(gdb) n274         s2 = rqlist->hibound + rqlist->lobound - 1.0;(gdb) 277         s2 += nulltestsel(root, IS_NULL, rqlist->var,#最终结果  (gdb) 325   return s1;(gdb) p s1$11 = 0.054823845775427538...

回到主函数:

(gdb) set_baserel_size_estimates (root=0x2686fa8, rel=0x26873b8) at costsize.c:43024302    nrows = rel->tuples *(gdb) 4309    rel->rows = clamp_row_est(nrows);(gdb) 4311    cost_qual_eval(&rel->baserestrictcost, rel->baserestrictinfo, root);(gdb) 4313    set_rel_width(root, rel);(gdb) p rel->rows$12 = 5482

结果为5482,执行计划中的rows=5482就是这么来的.

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