PostgreSQL物理优化中的create_index_paths->generate_bitmap_or_paths函数分析

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该函数从条件子句链表中寻找OR子句,如找到并且可以处理则生成BitmapOrPath。

下面是BitmapOrPath访问路径样例:

testdb=# explain verbose select t1.* from t_dwxx t1 where (dwbh > '10000' and dwbh < '30000') OR (dwdz between 'DWDZ10000' and 'DWDZ20000');QUERY PLAN                                                                                     --------------------------------------------------------------------------------------------- Bitmap Heap Scan on public.t_dwxx t1  (cost=84.38..216.82 rows=3156 width=20)   Output: dwmc, dwbh, dwdz   Recheck Cond: ((((t1.dwbh)::text > '10000'::text) AND ((t1.dwbh)::text < '30000'::text)) OR (((t1.dwdz)::text >= 'DWDZ10000'::text) AND ((t1.dwdz)::text <= 'DWDZ20000'::text)))   ->  BitmapOr  (cost=84.38..84.38 rows=3422 width=0)  -->BitmapOr         ->  Bitmap Index Scan on t_dwxx_pkey  (cost=0.00..50.52 rows=2223 width=0)               Index Cond: (((t1.dwbh)::text > '10000'::text) AND ((t1.dwbh)::text < '30000'::text))         ->  Bitmap Index Scan on idx_dwxx_dwdz  (cost=0.00..32.28 rows=1200 width=0)               Index Cond: (((t1.dwdz)::text >= 'DWDZ10000'::text) AND ((t1.dwdz)::text <= 'DWDZ20000'::text))(8 rows)

一、数据结构

Cost相关
注意:实际使用的参数值通过系统配置文件定义,而不是这里的常量定义!

 typedef double Cost; /* execution cost (in page-access units) */ /* defaults for costsize.c's Cost parameters */ /* NB: cost-estimation code should use the variables, not these constants! */ /* 注意:实际值通过系统配置文件定义,而不是这里的常量定义! */ /* If you change these, update backend/utils/misc/postgresql.sample.conf */ #define DEFAULT_SEQ_PAGE_COST  1.0       //顺序扫描page的成本 #define DEFAULT_RANDOM_PAGE_COST  4.0      //随机扫描page的成本 #define DEFAULT_CPU_TUPLE_COST  0.01     //处理一个元组的CPU成本 #define DEFAULT_CPU_INDEX_TUPLE_COST 0.005   //处理一个索引元组的CPU成本 #define DEFAULT_CPU_OPERATOR_COST  0.0025    //执行一次操作或函数的CPU成本 #define DEFAULT_PARALLEL_TUPLE_COST 0.1    //并行执行,从一个worker传输一个元组到另一个worker的成本 #define DEFAULT_PARALLEL_SETUP_COST  1000.0  //构建并行执行环境的成本  #define DEFAULT_EFFECTIVE_CACHE_SIZE  524288    /*先前已有介绍, measured in pages */ double      seq_page_cost = DEFAULT_SEQ_PAGE_COST; double      random_page_cost = DEFAULT_RANDOM_PAGE_COST; double      cpu_tuple_cost = DEFAULT_CPU_TUPLE_COST; double      cpu_index_tuple_cost = DEFAULT_CPU_INDEX_TUPLE_COST; double      cpu_operator_cost = DEFAULT_CPU_OPERATOR_COST; double      parallel_tuple_cost = DEFAULT_PARALLEL_TUPLE_COST; double      parallel_setup_cost = DEFAULT_PARALLEL_SETUP_COST;  int         effective_cache_size = DEFAULT_EFFECTIVE_CACHE_SIZE; Cost        disable_cost = 1.0e10;//1后面10个0,通过设置一个巨大的成本,让优化器自动放弃此路径  int         max_parallel_workers_per_gather = 2;//每次gather使用的worker数

二、源码解读

generate_bitmap_or_paths函数
create_index_paths->generate_bitmap_or_paths函数从条件子句链表中寻找OR子句,如找到并且可以处理则生成BitmapOrPath.函数返回生成的链表BitmapOrPaths.

 /*  * generate_bitmap_or_paths  *      Look through the list of clauses to find OR clauses, and generate  *      a BitmapOrPath for each one we can handle that way.  Return a list  *      of the generated BitmapOrPaths.  *   从条件子句链表中寻找OR子句,如找到并且可以处理则生成BitmapOrPath.  *     函数返回生成的链表BitmapOrPaths   *  * other_clauses is a list of additional clauses that can be assumed true  * for the purpose of generating indexquals, but are not to be searched for  * ORs.  (See build_paths_for_OR() for motivation.)  * other_clauses是一个附加子句链表，  * 为了生成索引条件，可以假定为true，但不能用于搜索OR子句。  */ static List * generate_bitmap_or_paths(PlannerInfo *root, RelOptInfo *rel,                          List *clauses, List *other_clauses) {     List       *result = NIL;     List       *all_clauses;     ListCell   *lc;      /*      * We can use both the current and other clauses as context for      * build_paths_for_OR; no need to remove ORs from the lists.      * 使用当前和其他子句作为build_paths_for_OR函数的输入参数      * 从而不需要从列表中删除OR子句。      */     all_clauses = list_concat(list_copy(clauses), other_clauses);//合并到链表中      foreach(lc, clauses)//遍历子句链表     {         RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);//约束条件         List       *pathlist;//路径链表         Path       *bitmapqual;//         ListCell   *j;          /* Ignore RestrictInfos that aren't ORs */         if (!restriction_is_or_clause(rinfo))//不是OR子句,处理下一个子句             continue;          /*          * We must be able to match at least one index to each of the arms of          * the OR, else we can't use it.          * 必须能够将至少一个索引匹配到OR的某个分支，否则无法使用索引。          */         pathlist = NIL;         foreach(j, ((BoolExpr *) rinfo->orclause)->args)//遍历OR子句参数         {             Node       *orarg = (Node *) lfirst(j);//参数节点             List       *indlist;              /* OR arguments should be ANDs or sub-RestrictInfos */             //OR子句的参数必须是AND子句或者是子约束条件             if (and_clause(orarg))//如为AND子句             {                 List       *andargs = ((BoolExpr *) orarg)->args;//获取AND子句的参数                  indlist = build_paths_for_OR(root, rel,                                              andargs,                                              all_clauses);//构建路径                  /* Recurse in case there are sub-ORs */                 //递归调用generate_bitmap_or_paths,并添加到访问路径链表中                 indlist = list_concat(indlist,                                       generate_bitmap_or_paths(root, rel,                                                                andargs,                                                                all_clauses));             }             else             {                 RestrictInfo *rinfo = castNode(RestrictInfo, orarg);//不是AND,则为约束条件                 List       *orargs;                  Assert(!restriction_is_or_clause(rinfo));                 orargs = list_make1(rinfo);                  indlist = build_paths_for_OR(root, rel,                                              orargs,                                              all_clauses);//构建访问路径             }              /*              * If nothing matched this arm, we can't do anything with this OR              * clause.              */             if (indlist == NIL)             {                 pathlist = NIL;                 break;             }              /*              * OK, pick the most promising AND combination, and add it to              * pathlist.              * 选择最有希望的组合，并将其添加到路径列表中。              */             bitmapqual = choose_bitmap_and(root, rel, indlist);             pathlist = lappend(pathlist, bitmapqual);         }          /*          * If we have a match for every arm, then turn them into a          * BitmapOrPath, and add to result list.          * 如果左右两边都匹配，那么将它们转换为BitmapOrPath，并添加到结果列表中。          */         if (pathlist != NIL)         {       //创建BitmapOrPath             bitmapqual = (Path *) create_bitmap_or_path(root, rel, pathlist);             result = lappend(result, bitmapqual);         }     }      return result; } //------------------------------------------------------ build_paths_for_OR /*  * build_paths_for_OR  *    Given a list of restriction clauses from one arm of an OR clause,  *    construct all matching IndexPaths for the relation.  *    给定OR子句的约束条件子句,构建该Relation所有匹配的索引访问路径.  *  * Here we must scan all indexes of the relation, since a bitmap OR tree  * can use multiple indexes.  * BitmapOr可能会使用多个索引,因此需要访问该Relation的所有索引.  *  * The caller actually supplies two lists of restriction clauses: some  * "current" ones and some "other" ones.  Both lists can be used freely  * to match keys of the index, but an index must use at least one of the  * "current" clauses to be considered usable.  The motivation for this is  * examples like  *      WHERE (x = 42) AND (... OR (y = 52 AND z = 77) OR ....)  * While we are considering the y/z subclause of the OR, we can use "x = 42"  * as one of the available index conditions; but we shouldn't match the  * subclause to any index on x alone, because such a Path would already have  * been generated at the upper level.  So we could use an index on x,y,z  * or an index on x,y for the OR subclause, but not an index on just x.  * When dealing with a partial index, a match of the index predicate to  * one of the "current" clauses also makes the index usable.  * 函数调用方提供了2个约束条件子句链表,一个是"current",另外一个是"other".  * 这两个链表都可以用于资源匹配索引键,但是索引必须使用至少一个存在于"current"中的子句.   * 举个例子,有下面的条件语句:  *     WHERE (x = 42) AND (... OR (y = 52 AND z = 77) OR ....)  * 在考察OR中的x/z子句时,可以使用"x = 42"作为可用的索引条件,但  * 但不应该将子句单独与x上的任何索引进行匹配，因为这样的访问路径已经在上层生成。  * 因此可以在OR子句上使用x,y,z上索引或x,y上的索引,但不能是x上的索引.  * 在处理部分索引时,与索引谓词匹配的"current"子句同样可以使用此索引.  *  * 'rel' is the relation for which we want to generate index paths  * 'clauses' is the current list of clauses (RestrictInfo nodes)  * 'other_clauses' is the list of additional upper-level clauses  * 输入参数:  * rel-需要生成访问路径的Relation   * clauses-"current"子句,节点类型为RestrictInfo  * other_clauses-"other"子句,上层子句已处理  */ static List * build_paths_for_OR(PlannerInfo *root, RelOptInfo *rel,                    List *clauses, List *other_clauses) {     List       *result = NIL;//返回结果     List       *all_clauses = NIL;  /* not computed till needed */     ListCell   *lc;//临时变量      foreach(lc, rel->indexlist)//遍历RelOptInfo上的Index     {         IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);//IndexOptInfo         IndexClauseSet clauseset;//         List       *indexpaths;         bool        useful_predicate;          /* Ignore index if it doesn't support bitmap scans */         if (!index->amhasgetbitmap)//索引不支持BitmapIndexScan             continue;          /*          * Ignore partial indexes that do not match the query.  If a partial          * index is marked predOK then we know it's OK.  Otherwise, we have to          * test whether the added clauses are sufficient to imply the          * predicate. If so, we can use the index in the current context.          * 忽略不匹配查询的部分索引。如predOK标记为T,则可考虑使用此索引.          * 否则，必须测试添加的子句是否足以包含索引谓词.          * 在这种情况下才可以在当前上下文中使用索引。          *          * We set useful_predicate to true iff the predicate was proven using          * the current set of clauses.  This is needed to prevent matching a          * predOK index to an arm of an OR, which would be a legal but          * pointlessly inefficient plan.  (A better plan will be generated by          * just scanning the predOK index alone, no OR.)          * 如验证通过,则将useful_predicate设置为T。      * 这是为了避免predOK索引与OR的某个分支相匹配，这是一个合法但无意义的低效计划。      * (只需要扫描部分索引就可以产生一个更好的计划，但不是OR子句)          */         useful_predicate = false;         if (index->indpred != NIL)         {             if (index->predOK)             {                 /* Usable, but don't set useful_predicate */             }             else             {                 /* Form all_clauses if not done already */                 if (all_clauses == NIL)                     all_clauses = list_concat(list_copy(clauses),                                               other_clauses);                  if (!predicate_implied_by(index->indpred, all_clauses, false))                     continue;   /* can't use it at all */                  if (!predicate_implied_by(index->indpred, other_clauses, false))                     useful_predicate = true;             }         }          /*          * Identify the restriction clauses that can match the index.          * 标记与索引匹配的约束条件子句          */         MemSet(&clauseset, 0, sizeof(clauseset));         match_clauses_to_index(index, clauses, &clauseset);          /*          * If no matches so far, and the index predicate isn't useful, we          * don't want it.          */         if (!clauseset.nonempty && !useful_predicate)//没有合适的,继续下一个索引             continue;          /*          * Add "other" restriction clauses to the clauseset.          */         match_clauses_to_index(index, other_clauses, &clauseset);//添加到clauseset中          /*          * Construct paths if possible.          */         indexpaths = build_index_paths(root, rel,                                        index, &clauseset,                                        useful_predicate,                                        ST_BITMAPSCAN,                                        NULL,                                        NULL);//构建索引访问路径         result = list_concat(result, indexpaths);     }      return result; } //------------------------------------------------------ create_bitmap_or_path /*  * create_bitmap_or_path  *    Creates a path node representing a BitmapOr.  *    创建BitmapOr路径节点  */ BitmapOrPath * create_bitmap_or_path(PlannerInfo *root,                       RelOptInfo *rel,                       List *bitmapquals) {     BitmapOrPath *pathnode = makeNode(BitmapOrPath);      pathnode->path.pathtype = T_BitmapOr;     pathnode->path.parent = rel;     pathnode->path.pathtarget = rel->reltarget;     pathnode->path.param_info = NULL;   /* not used in bitmap trees */      /*      * Currently, a BitmapHeapPath, BitmapAndPath, or BitmapOrPath will be      * parallel-safe if and only if rel->consider_parallel is set.  So, we can      * set the flag for this path based only on the relation-level flag,      * without actually iterating over the list of children.      */     pathnode->path.parallel_aware = false;     pathnode->path.parallel_safe = rel->consider_parallel;     pathnode->path.parallel_workers = 0;      pathnode->path.pathkeys = NIL;  /* always unordered */      pathnode->bitmapquals = bitmapquals;      /* this sets bitmapselectivity as well as the regular cost fields: */     cost_bitmap_or_node(pathnode, root);//计算成本      return pathnode; }//------------------------------------ create_bitmap_or_path /*  * cost_bitmap_or_node  *      Estimate the cost of a BitmapOr node  *      估算BitmapOr成本  *  * See comments for cost_bitmap_and_node.  */ void cost_bitmap_or_node(BitmapOrPath *path, PlannerInfo *root) {     Cost        totalCost;     Selectivity selec;     ListCell   *l;      /*      * We estimate OR selectivity on the assumption that the inputs are      * non-overlapping, since that's often the case in "x IN (list)" type      * situations.  Of course, we clamp to 1.0 at the end.      * 我们估算或计算选择率的前提是输入不重叠，因为存在"x in (list)"这样的情况。      * 当然，我们在最后调整为1.0。    *      * The runtime cost of the BitmapOr itself is estimated at 100x      * cpu_operator_cost for each tbm_union needed.  Probably too small,      * definitely too simplistic?  We are aware that the tbm_unions are      * optimized out when the inputs are BitmapIndexScans.      * 对于所需的每个tbm_union操作,       * BitmapOr本身的运行时成本估计为100 x cpu_operator_cost。      * 这个估值是否太小，太简单了?其实，当输入是位图索引扫描时，tbm_unions已被优化。      */     totalCost = 0.0;//成本     selec = 0.0;//选择率     foreach(l, path->bitmapquals)//遍历条件     {         Path       *subpath = (Path *) lfirst(l);//路径         Cost        subCost;//成本         Selectivity subselec;          cost_bitmap_tree_node(subpath, &subCost, &subselec);//遍历路径获取成本&选择率          selec += subselec;//          totalCost += subCost;         if (l != list_head(path->bitmapquals) &&             !IsA(subpath, IndexPath))             totalCost += 100.0 * cpu_operator_cost;//非单个条件而且不是索引访问路径,则添加运行期成本     }     path->bitmapselectivity = Min(selec, 1.0);//选择率     path->path.rows = 0;        /* per above, not used */     path->path.startup_cost = totalCost;     path->path.total_cost = totalCost; }

三、跟踪分析

测试脚本如下

select t1.* from t_dwxx t1 where (dwbh > '10000' and dwbh < '30000')       OR (dwdz between 'DWDZ10000' and 'DWDZ20000');

启动gdb跟踪

(gdb) b generate_bitmap_or_pathsBreakpoint 1 at 0x74e6c1: file indxpath.c, line 1266.(gdb) cContinuing.Breakpoint 1, generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaf138, other_clauses=0x0)    at indxpath.c:12661266    List     *result = NIL;

查看输入参数,clauses是链表,只有一个元素(BoolExpr类型,即OR子句);other_clauses为NULL

(gdb) p *clauses$1 = {type = T_List, length = 1, head = 0x2aaf118, tail = 0x2aaf118}(gdb) p *(Node *)clauses->head->data.ptr_value$2 = {type = T_RestrictInfo}(gdb) p *(RestrictInfo *)clauses->head->data.ptr_value$3 = {type = T_RestrictInfo, clause = 0x2aad818, is_pushed_down = true, outerjoin_delayed = false, can_join = false,   pseudoconstant = false, leakproof = false, security_level = 0, clause_relids = 0x2aaf100, required_relids = 0x2aae938,   outer_relids = 0x0, nullable_relids = 0x0, left_relids = 0x0, right_relids = 0x0, orclause = 0x2aaefc0, parent_ec = 0x0,   eval_cost = {startup = 0, per_tuple = 0.01}, norm_selec = 0.31556115090433856, outer_selec = -1, mergeopfamilies = 0x0,   left_ec = 0x0, right_ec = 0x0, left_em = 0x0, right_em = 0x0, scansel_cache = 0x0, outer_is_left = false,   hashjoinoperator = 0, left_bucketsize = -1, right_bucketsize = -1, left_mcvfreq = -1, right_mcvfreq = -1}(gdb) p *((RestrictInfo *)clauses->head->data.ptr_value)->clause$4 = {type = T_BoolExpr}(gdb) set $clause=((RestrictInfo *)clauses->head->data.ptr_value)->clause(gdb) p *(BoolExpr *)$clause$6 = {xpr = {type = T_BoolExpr}, boolop = OR_EXPR, args = 0x2aad758, location = -1}

遍历clausees子句,rinfo->clause即BoolExpr(OR子句)

...1276    foreach(lc, clauses)(gdb) 1278      RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);(gdb) 1284      if (!restriction_is_or_clause(rinfo))

遍历OR子句的参数

(gdb) 1292      foreach(j, ((BoolExpr *) rinfo->orclause)->args)

参数的第一个元素,BoolExpr,boolop操作符为AND_EXPR

(gdb) n1294        Node     *orarg = (Node *) lfirst(j);(gdb) 1298        if (and_clause(orarg))(gdb) p *orarg$10 = {type = T_BoolExpr}(gdb) p *(BoolExpr *)orarg$11 = {xpr = {type = T_BoolExpr}, boolop = AND_EXPR, args = 0x2aaea90, location = -1}

AND子句的参数

(gdb) n1300          List     *andargs = ((BoolExpr *) orarg)->args;(gdb) 1302          indlist = build_paths_for_OR(root, rel,(gdb) p *andargs$12 = {type = T_List, length = 2, head = 0x2aada78, tail = 0x2aada98}(gdb) p *(Node *)andargs->head->data.ptr_value$13 = {type = T_RestrictInfo}(gdb) p *(RestrictInfo *)andargs->head->data.ptr_value$14 = {type = T_RestrictInfo, clause = 0x2aace08, is_pushed_down = true, outerjoin_delayed = false, can_join = false,   pseudoconstant = false, leakproof = false, security_level = 0, clause_relids = 0x2aaea78, required_relids = 0x2aaea78,   outer_relids = 0x0, nullable_relids = 0x0, left_relids = 0x2aaea60, right_relids = 0x0, orclause = 0x0, parent_ec = 0x0,   eval_cost = {startup = 0, per_tuple = 0.0025000000000000001}, norm_selec = 0.99990000000000001, outer_selec = -1,   mergeopfamilies = 0x0, left_ec = 0x0, right_ec = 0x0, left_em = 0x0, right_em = 0x0, scansel_cache = 0x0,   outer_is_left = false, hashjoinoperator = 0, left_bucketsize = -1, right_bucketsize = -1, left_mcvfreq = -1,   right_mcvfreq = -1}(gdb) p *((RestrictInfo *)andargs->head->data.ptr_value)->clause$15 = {type = T_OpExpr}(gdb) set $tmp=((RestrictInfo *)andargs->head->data.ptr_value)->clause(gdb) p *(OpExpr *)$tmp$16 = {xpr = {type = T_OpExpr}, opno = 666, opfuncid = 742, opresulttype = 16, opretset = false, opcollid = 0,   inputcollid = 100, args = 0x2aacd68, location = 39}(gdb) set $tmp2=((RestrictInfo *)andargs->head->next->data.ptr_value)->clause(gdb) p *(OpExpr *)$tmp2$17 = {xpr = {type = T_OpExpr}, opno = 664, opfuncid = 740, opresulttype = 16, opretset = false, opcollid = 0,   inputcollid = 100, args = 0x2aacc78, location = 58}(gdb)

进入build_paths_for_OR函数

(gdb) stepbuild_paths_for_OR (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaea90, other_clauses=0x2aaf598) at indxpath.c:11701170    List     *result = NIL;

遍历索引,第一个索引是idx_dwxx_dwdz

1174    foreach(lc, rel->indexlist)(gdb) 1176      IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);(gdb) 1182      if (!index->amhasgetbitmap)(gdb) p *index$18 = {type = T_IndexOptInfo, indexoid = 16753, reltablespace = 0, rel = 0x2aa6658, pages = 40, tuples = 10000,   tree_height = 1, ncolumns = 1, nkeycolumns = 1, indexkeys = 0x2aae590, indexcollations = 0x2aae5a8, opfamily = 0x2aae5c0,   opcintype = 0x2aae5d8, sortopfamily = 0x2aae5c0, reverse_sort = 0x2aae608, nulls_first = 0x2aae620,   canreturn = 0x2aae5f0, relam = 403, indexprs = 0x0, indpred = 0x0, indextlist = 0x2aae6f8, indrestrictinfo = 0x2aaf138,   predOK = false, unique = false, immediate = true, hypothetical = false, amcanorderbyop = false, amoptionalkey = true,   amsearcharray = true, amsearchnulls = true, amhasgettuple = true, amhasgetbitmap = true, amcanparallel = true,   amcostestimate = 0x94f0ad }--testdb=# select relname from pg_class where oid=16753;    relname    --------------- idx_dwxx_dwdz(1 row)--

与约束条件不匹配((dwbh > '10000' and dwbh < '30000')),继续下一个索引

1229      if (!clauseset.nonempty && !useful_predicate)(gdb) p clauseset$20 = {nonempty = false, indexclauses = {0x0 }}(gdb) n1230        continue;

下一个索引是idx_dwxx_predicate_dwmc/idx_dwxx_expr,同样不匹配,继续寻找索引,直至索引t_dwxx_pkey

(gdb) p *index$23 = {type = T_IndexOptInfo, indexoid = 16738,...1223      match_clauses_to_index(index, clauses, &clauseset);(gdb) 1229      if (!clauseset.nonempty && !useful_predicate)(gdb) p clauseset$24 = {nonempty = true, indexclauses = {0x2aaf638, 0x0 }}

构建索引访问路径

(gdb) 1246      result = list_concat(result, indexpaths);(gdb) p *indexpaths$25 = {type = T_List, length = 1, head = 0x2aafb48, tail = 0x2aafb48}(gdb) p *(Node *)indexpaths->head->data.ptr_value$26 = {type = T_IndexPath}(gdb) p *(IndexPath *)indexpaths->head->data.ptr_value$27 = {path = {type = T_IndexPath, pathtype = T_IndexScan, parent = 0x2aa6658, pathtarget = 0x2aad8d8, param_info = 0x0,     parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 3156, startup_cost = 0.28500000000000003,     total_cost = 191.46871600907946, pathkeys = 0x0}, indexinfo = 0x2aa6868, indexclauses = 0x2aaf6a8,   indexquals = 0x2aaf898, indexqualcols = 0x2aaf8e8, indexorderbys = 0x0, indexorderbycols = 0x0,   indexscandir = ForwardScanDirection, indextotalcost = 50.515000000000001, indexselectivity = 0.22227191011235958}

回到generate_bitmap_or_paths函数

1250  }(gdb) generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaf138, other_clauses=0x0) at indxpath.c:13071307          indlist = list_concat(indlist,

递归进入generate_bitmap_or_paths

(gdb) nBreakpoint 1, generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaea90, other_clauses=0x2aaf598)    at indxpath.c:12661266    List     *result = NIL;#直接结束(gdb) finishRun till exit from #0  generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaea90, other_clauses=0x2aaf598)    at indxpath.c:12660x000000000074e7a0 in generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaf138, other_clauses=0x0)    at indxpath.c:13071307          indlist = list_concat(indlist,Value returned is $28 = (List *) 0x0

完成第一轮循环

(gdb) n1329        if (indlist == NIL)(gdb) n1339        bitmapqual = choose_bitmap_and(root, rel, indlist);(gdb) 1340        pathlist = lappend(pathlist, bitmapqual);(gdb) p *bitmapqual$29 = {type = T_IndexPath, pathtype = T_IndexScan, parent = 0x2aa6658, pathtarget = 0x2aad8d8, param_info = 0x0,   parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 3156, startup_cost = 0.28500000000000003,   total_cost = 191.46871600907946, pathkeys = 0x0}

这是第二个AND子句

1292      foreach(j, ((BoolExpr *) rinfo->orclause)->args)(gdb) 1294        Node     *orarg = (Node *) lfirst(j);(gdb) 1298        if (and_clause(orarg))(gdb) 1300          List     *andargs = ((BoolExpr *) orarg)->args;

完成第二轮循环

(gdb) 1339        bitmapqual = choose_bitmap_and(root, rel, indlist);(gdb) 1340        pathlist = lappend(pathlist, bitmapqual);(gdb) p bitmapqual$33 = (Path *) 0x2aafd78(gdb) p *bitmapqual$34 = {type = T_IndexPath, pathtype = T_IndexScan, parent = 0x2aa6658, pathtarget = 0x2aad8d8, param_info = 0x0,   parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 3156, startup_cost = 0.28500000000000003,   total_cost = 148.08735471522883, pathkeys = 0x0}

结束循环,构建BitmapOrPath

1347      if (pathlist != NIL)(gdb) 1349        bitmapqual = (Path *) create_bitmap_or_path(root, rel, pathlist);

进入create_bitmap_or_path,调用函数cost_bitmap_or_node计算成本

(gdb) stepcreate_bitmap_or_path (root=0x2aa6248, rel=0x2aa6658, bitmapquals=0x2aafbf8) at pathnode.c:11561156    BitmapOrPath *pathnode = makeNode(BitmapOrPath);...1178    cost_bitmap_or_node(pathnode, root);(gdb) stepcost_bitmap_or_node (path=0x2ab0278, root=0x2aa6248) at costsize.c:1149...

计算结果,与执行计划中的信息相匹配"BitmapOr (cost=84.38..84.38 rows=3422 width=0)"

(gdb) p *path$37 = {path = {type = T_BitmapOrPath, pathtype = T_BitmapOr, parent = 0x2aa6658, pathtarget = 0x2aad8d8, param_info = 0x0,     parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 0, startup_cost = 84.378,     total_cost = 84.378, pathkeys = 0x0}, bitmapquals = 0x2aafbf8, bitmapselectivity = 0.34222288270157986}

回到generate_bitmap_or_paths

(gdb) ncreate_bitmap_or_path (root=0x2aa6248, rel=0x2aa6658, bitmapquals=0x2aafbf8) at pathnode.c:11801180    return pathnode;(gdb) 1181  }(gdb) generate_bitmap_or_paths (root=0x2aa6248, rel=0x2aa6658, clauses=0x2aaf138, other_clauses=0x0) at indxpath.c:13501350        result = lappend(result, bitmapqual);

感谢各位的阅读，以上就是"PostgreSQL物理优化中的create_index_paths->generate_bitmap_or_paths函数分析"的内容了，经过本文的学习后，相信大家对PostgreSQL物理优化中的create_index_paths->generate_bitmap_or_paths函数分析这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是，小编将为大家推送更多相关知识点的文章，欢迎关注！