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PostgreSQL 源码解读(70)- 查询语句#55(make_one_rel函数#20-...

原创 PostgreSQL 作者:husthxd 时间:2018-10-26 10:57:00 0 删除 编辑

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->populate_joinrel_with_paths->add_paths_to_joinrel函数中的hash_inner_and_outer函数,该函数尝试构造hash join访问路径。

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

hash join的算法实现伪代码如下:
Step 1
FOR small_table_row IN (SELECT * FROM small_table)
LOOP
slot := HASH(small_table_row.join_key);
INSERT_HASH_TABLE(slot,small_table_row);
END LOOP;

Step 2
FOR large_table_row IN (SELECT * FROM large_table) LOOP
slot := HASH(large_table_row.join_key);
small_table_row = LOOKUP_HASH_TABLE(slot,large_table_row.join_key);
IF small_table_row FOUND THEN
output small_table_row + large_table_row;
END IF;
END LOOP;

hash_inner_and_outer
该函数创建hash join访问路径。


//------------------------------------------------ hash_inner_and_outer

/*
 * hash_inner_and_outer
 *    Create hashjoin join paths by explicitly hashing both the outer and
 *    inner keys of each available hash clause.
 *    通过显式对外表和内表(应用每个可用的hash条件)进行hash操作,创建hash join访问路径
 *
 * 'joinrel' is the join relation
 * 'outerrel' is the outer join relation
 * 'innerrel' is the inner join relation
 * 'jointype' is the type of join to do
 * 'extra' contains additional input values
 */
static void
hash_inner_and_outer(PlannerInfo *root,
                     RelOptInfo *joinrel,
                     RelOptInfo *outerrel,
                     RelOptInfo *innerrel,
                     JoinType jointype,
                     JoinPathExtraData *extra)
{
    JoinType    save_jointype = jointype;
    bool        isouterjoin = IS_OUTER_JOIN(jointype);
    List       *hashclauses;
    ListCell   *l;

    /*
     * We need to build only one hashclauses list for any given pair of outer
     * and inner relations; all of the hashable clauses will be used as keys.
     * 只需要为给定的外表和内表对构建一个hashclauses条件链表;所有的hashable子句将用作hash键。
     *
     * Scan the join's restrictinfo list to find hashjoinable clauses that are
     * usable with this pair of sub-relations.
     * 扫描连接的约束条件restrictinfo链表,找到可用于这对子关系的hash连接hashjoinable子句。
     */
    hashclauses = NIL;
    foreach(l, extra->restrictlist)
    {
        RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(l);

        /*
         * If processing an outer join, only use its own join clauses for
         * hashing.  For inner joins we need not be so picky.
         * 如果处理外连接,则仅使用其自己的连接子句进行哈希操作。对于内连接,则无需如此操作。
         */
        if (isouterjoin && RINFO_IS_PUSHED_DOWN(restrictinfo, joinrel->relids))
            continue;

        if (!restrictinfo->can_join ||
            restrictinfo->hashjoinoperator == InvalidOid)
            continue;           /* 不能被hash.not hashjoinable */

        /*
         * Check if clause has the form "outer op inner" or "inner op outer".
         * 检查条件是否有形如outer op inner或者inner op outer的形式
         */
        if (!clause_sides_match_join(restrictinfo, outerrel, innerrel))
            continue;           /* no good for these input relations */

        hashclauses = lappend(hashclauses, restrictinfo);//加入到hash条件中
    }

    /* If we found any usable hashclauses, make paths */
    //如发现可用于hash连接的条件,则构建hash连接访问路径,如无则无法构建
    if (hashclauses)
    {
        /*
         * We consider both the cheapest-total-cost and cheapest-startup-cost
         * outer paths.  There's no need to consider any but the
         * cheapest-total-cost inner path, however.
         * 外表:既考虑了成本最低的总成本,也考虑了外表启动成本最低的访问路径。
         * 内表:除了成本最低的内部路径之外,不需要考虑任何其他路径。
         */
        Path       *cheapest_startup_outer = outerrel->cheapest_startup_path;
        Path       *cheapest_total_outer = outerrel->cheapest_total_path;
        Path       *cheapest_total_inner = innerrel->cheapest_total_path;

        /*
         * If either cheapest-total path is parameterized by the other rel, we
         * can't use a hashjoin.  (There's no use looking for alternative
         * input paths, since these should already be the least-parameterized
         * available paths.)
         * 如果其中一个关系参数化了其中一个成本最低的访问路径,那么不能使用hash join。
         * (没有必要寻找替代的输入路径,因为这些路径应该已经是参数化最少的可用路径了。)
         */
        if (PATH_PARAM_BY_REL(cheapest_total_outer, innerrel) ||
            PATH_PARAM_BY_REL(cheapest_total_inner, outerrel))
            return;//直接退出

        /* Unique-ify if need be; we ignore parameterized possibilities */
        //如果需要保证唯一性,丢弃参数化
        if (jointype == JOIN_UNIQUE_OUTER)
        {
            cheapest_total_outer = (Path *)
                create_unique_path(root, outerrel,
                                   cheapest_total_outer, extra->sjinfo);
            Assert(cheapest_total_outer);
            jointype = JOIN_INNER;
            try_hashjoin_path(root,
                              joinrel,
                              cheapest_total_outer,
                              cheapest_total_inner,
                              hashclauses,
                              jointype,
                              extra);
            /* no possibility of cheap startup here */
        }
        else if (jointype == JOIN_UNIQUE_INNER)
        {
            cheapest_total_inner = (Path *)
                create_unique_path(root, innerrel,
                                   cheapest_total_inner, extra->sjinfo);
            Assert(cheapest_total_inner);
            jointype = JOIN_INNER;
            try_hashjoin_path(root,
                              joinrel,
                              cheapest_total_outer,
                              cheapest_total_inner,
                              hashclauses,
                              jointype,
                              extra);
            if (cheapest_startup_outer != NULL &&
                cheapest_startup_outer != cheapest_total_outer)
                try_hashjoin_path(root,
                                  joinrel,
                                  cheapest_startup_outer,
                                  cheapest_total_inner,
                                  hashclauses,
                                  jointype,
                                  extra);
        }
        else//其他连接类型
        {
            /*
             * For other jointypes, we consider the cheapest startup outer
             * together with the cheapest total inner, and then consider
             * pairings of cheapest-total paths including parameterized ones.
             * There is no use in generating parameterized paths on the basis
             * of possibly cheap startup cost, so this is sufficient.
             * 对于其他连接类型,我们考虑成本最低的的外表启动和内表启动访问路径,
             * 然后考虑包括参数化路径在内的成本最低的访问路径对。
             * 在基于可能较低的启动成本的基础上生成参数化路径是没有用的,上面的做法就足够了。
             */
            ListCell   *lc1;
            ListCell   *lc2;

            if (cheapest_startup_outer != NULL)//启动成本最低的外表访问路径
                try_hashjoin_path(root,
                                  joinrel,
                                  cheapest_startup_outer,
                                  cheapest_total_inner,
                                  hashclauses,
                                  jointype,
                                  extra);//构建hash join访问路径

            foreach(lc1, outerrel->cheapest_parameterized_paths)//遍历外表参数化路径
            {
                Path       *outerpath = (Path *) lfirst(lc1);

                /*
                 * We cannot use an outer path that is parameterized by the
                 * inner rel.
                 * 不能使用被内表参数化使用的外表访问路径
                 */
                if (PATH_PARAM_BY_REL(outerpath, innerrel))
                    continue;

                foreach(lc2, innerrel->cheapest_parameterized_paths)//遍历内表参数化路径
                {
                    Path       *innerpath = (Path *) lfirst(lc2);

                    /*
                     * We cannot use an inner path that is parameterized by
                     * the outer rel, either.
                     * 同样的,不能使用被外表参数化使用的内表访问路径
                     */
                    if (PATH_PARAM_BY_REL(innerpath, outerrel))
                        continue;

                    if (outerpath == cheapest_startup_outer &&
                        innerpath == cheapest_total_inner)
                        continue;   /* already tried it */

                    try_hashjoin_path(root,
                                      joinrel,
                                      outerpath,
                                      innerpath,
                                      hashclauses,
                                      jointype,
                                      extra);//构建hash连接访问路径
                }
            }
        }

        /*
         * If the joinrel is parallel-safe, we may be able to consider a
         * partial hash join.  However, we can't handle JOIN_UNIQUE_OUTER,
         * because the outer path will be partial, and therefore we won't be
         * able to properly guarantee uniqueness.  Similarly, we can't handle
         * JOIN_FULL and JOIN_RIGHT, because they can produce false null
         * extended rows.  Also, the resulting path must not be parameterized.
         * We would be able to support JOIN_FULL and JOIN_RIGHT for Parallel
         * Hash, since in that case we're back to a single hash table with a
         * single set of match bits for each batch, but that will require
         * figuring out a deadlock-free way to wait for the probe to finish.
         * 如果连接是并行安全的,可以考虑并行哈希连接。
         * 但是,我们不能处理JOIN_UNIQUE_OUTER,因为外部路径是部分的,因此我们不能正确地保证惟一性。
         * 类似地,我们不能处理JOIN_FULL和JOIN_RIGHT,因为它们会产生假空扩展行。
         * 此外,生成的路径不能被参数化。
         * 我们将能够支持JOIN_FULL和JOIN_RIGHT用于并行哈希,
         * 因为在这种情况下,我们将返回到一个哈希表,每个批处理只有一组匹配位,
         * 但这需要找到一种没有死锁的方式来等待探测完成。
         */
        if (joinrel->consider_parallel &&
            save_jointype != JOIN_UNIQUE_OUTER &&
            save_jointype != JOIN_FULL &&
            save_jointype != JOIN_RIGHT &&
            outerrel->partial_pathlist != NIL &&
            bms_is_empty(joinrel->lateral_relids))
        {
            Path       *cheapest_partial_outer;
            Path       *cheapest_partial_inner = NULL;
            Path       *cheapest_safe_inner = NULL;

            cheapest_partial_outer =
                (Path *) linitial(outerrel->partial_pathlist);

            /*
             * Can we use a partial inner plan too, so that we can build a
             * shared hash table in parallel?
             * 我们是否也可以使用部分内表访问路径,以便并行构建共享哈希表?
             */
            if (innerrel->partial_pathlist != NIL && enable_parallel_hash)
            {
                cheapest_partial_inner =
                    (Path *) linitial(innerrel->partial_pathlist);
                try_partial_hashjoin_path(root, joinrel,
                                          cheapest_partial_outer,
                                          cheapest_partial_inner,
                                          hashclauses, jointype, extra,
                                          true /* parallel_hash */ );
            }

            /*
             * Normally, given that the joinrel is parallel-safe, the cheapest
             * total inner path will also be parallel-safe, but if not, we'll
             * have to search for the cheapest safe, unparameterized inner
             * path.  If doing JOIN_UNIQUE_INNER, we can't use any alternative
             * inner path.
             * 通常,假设连接是并行安全的,最便宜的总内表访问路径也是并行安全的,
             * 但如果不是,我们将不得不寻找成本最低的安全的、非参数化的内表访问路径。
             * 如果执行JOIN_UNIQUE_INNER,则不能使用任何替代的内表访问路径。
             */
            if (cheapest_total_inner->parallel_safe)
                cheapest_safe_inner = cheapest_total_inner;
            else if (save_jointype != JOIN_UNIQUE_INNER)
                cheapest_safe_inner =
                    get_cheapest_parallel_safe_total_inner(innerrel->pathlist);

            if (cheapest_safe_inner != NULL)
                try_partial_hashjoin_path(root, joinrel,
                                          cheapest_partial_outer,
                                          cheapest_safe_inner,
                                          hashclauses, jointype, extra,
                                          false /* parallel_hash */ );
        }
    }
}
 

//----------------------------- try_hashjoin_path

 /*
  * try_hashjoin_path
  *    Consider a hash join path; if it appears useful, push it into
  *    the joinrel's pathlist via add_path().
  *    尝试构造hash join访问路径.
  *    如果该访问路径可用,通过add_path函数添加到连接新生成的关系joinrel中的pathlist链表中
  */
 static void
 try_hashjoin_path(PlannerInfo *root,
                   RelOptInfo *joinrel,
                   Path *outer_path,
                   Path *inner_path,
                   List *hashclauses,
                   JoinType jointype,
                   JoinPathExtraData *extra)
 {
     Relids      required_outer;
     JoinCostWorkspace workspace;
 
     /*
      * Check to see if proposed path is still parameterized, and reject if the
      * parameterization wouldn't be sensible.
      * 检查建议的路径是否仍然是参数化的,如果参数化不合理,则拒绝。
      * 
      */
     required_outer = calc_non_nestloop_required_outer(outer_path,
                                                       inner_path);
     if (required_outer &&
         !bms_overlap(required_outer, extra->param_source_rels))
     {
         /* Waste no memory when we reject a path here */
         bms_free(required_outer);
         return;
     }
 
     /*
      * See comments in try_nestloop_path().  Also note that hashjoin paths
      * never have any output pathkeys, per comments in create_hashjoin_path.
      * 参见try_nestloop_path()中的注释。
      * 还要注意,hash join访问路径从来没有任何输出路径键,参见create_hashjoin_path中的注释.
      */
     initial_cost_hashjoin(root, &workspace, jointype, hashclauses,
                           outer_path, inner_path, extra, false);//初步估算成本
 
     if (add_path_precheck(joinrel,
                           workspace.startup_cost, workspace.total_cost,
                           NIL, required_outer))//初始判断
     {
         add_path(joinrel, (Path *)
                  create_hashjoin_path(root,
                                       joinrel,
                                       jointype,
                                       &workspace,
                                       extra,
                                       outer_path,
                                       inner_path,
                                       false,    /* parallel_hash */
                                       extra->restrictlist,
                                       required_outer,
                                       hashclauses));//创建hash join访问路径,并添加
     }
     else
     {
         /* Waste no memory when we reject a path here */
         bms_free(required_outer);
     }
 }
 

//------------------ create_hashjoin_path

 /*
  * create_hashjoin_path
  *    Creates a pathnode corresponding to a hash join between two relations.
  *    创建hash join访问路径Node
  *
  * 'joinrel' is the join relation
  * 'jointype' is the type of join required
  * 'workspace' is the result from initial_cost_hashjoin
  * 'extra' contains various information about the join
  * 'outer_path' is the cheapest outer path
  * 'inner_path' is the cheapest inner path
  * 'parallel_hash' to select Parallel Hash of inner path (shared hash table)
  * 'restrict_clauses' are the RestrictInfo nodes to apply at the join
  * 'required_outer' is the set of required outer rels
  * 'hashclauses' are the RestrictInfo nodes to use as hash clauses
  *      (this should be a subset of the restrict_clauses list)
  */
 HashPath *
 create_hashjoin_path(PlannerInfo *root,
                      RelOptInfo *joinrel,
                      JoinType jointype,
                      JoinCostWorkspace *workspace,
                      JoinPathExtraData *extra,
                      Path *outer_path,
                      Path *inner_path,
                      bool parallel_hash,
                      List *restrict_clauses,
                      Relids required_outer,
                      List *hashclauses)
 {
     HashPath   *pathnode = makeNode(HashPath);
 
     pathnode->jpath.path.pathtype = T_HashJoin;
     pathnode->jpath.path.parent = joinrel;
     pathnode->jpath.path.pathtarget = joinrel->reltarget;
     pathnode->jpath.path.param_info =
         get_joinrel_parampathinfo(root,
                                   joinrel,
                                   outer_path,
                                   inner_path,
                                   extra->sjinfo,
                                   required_outer,
                                   &restrict_clauses);
     pathnode->jpath.path.parallel_aware =
         joinrel->consider_parallel && parallel_hash;
     pathnode->jpath.path.parallel_safe = joinrel->consider_parallel &&
         outer_path->parallel_safe && inner_path->parallel_safe;
     /* This is a foolish way to estimate parallel_workers, but for now... */
     pathnode->jpath.path.parallel_workers = outer_path->parallel_workers;
 
     /*
      * A hashjoin never has pathkeys, since its output ordering is
      * unpredictable due to possible batching.  XXX If the inner relation is
      * small enough, we could instruct the executor that it must not batch,
      * and then we could assume that the output inherits the outer relation's
      * ordering, which might save a sort step.  However there is considerable
      * downside if our estimate of the inner relation size is badly off. For
      * the moment we don't risk it.  (Note also that if we wanted to take this
      * seriously, joinpath.c would have to consider many more paths for the
      * outer rel than it does now.)
      * hashjoin从来没有路径键,因为由于可能的批处理,其输出顺序不可预测。
      * 如果内部关系足够小,可以指示执行器它不执行批处理,然后可以假设输出继承外部关系的顺序,这样可以节省排序步骤。
      * 然而,如果对内部关系大小的估计严重不足,就会有相当大的负面影响。
      * (还要注意,如果我们想认真对待这个问题,那就是joinpath.c将不得不考虑比现在更多的外表访问路径。)
      */
     pathnode->jpath.path.pathkeys = NIL;
     pathnode->jpath.jointype = jointype;
     pathnode->jpath.inner_unique = extra->inner_unique;
     pathnode->jpath.outerjoinpath = outer_path;
     pathnode->jpath.innerjoinpath = inner_path;
     pathnode->jpath.joinrestrictinfo = restrict_clauses;
     pathnode->path_hashclauses = hashclauses;
     /* final_cost_hashjoin will fill in pathnode->num_batches */
 
     final_cost_hashjoin(root, pathnode, workspace, extra);//最终的成本估算
 
     return pathnode;
 }

三、跟踪分析

测试脚本如下

testdb=# explain verbose select dw.*,grjf.grbh,grjf.xm,grjf.ny,grjf.je 
testdb-# from t_dwxx dw,lateral (select gr.grbh,gr.xm,jf.ny,jf.je 
testdb(#                         from t_grxx gr inner join t_jfxx jf 
testdb(#                                        on gr.dwbh = dw.dwbh 
testdb(#                                           and gr.grbh = jf.grbh) grjf
testdb-# order by dw.dwbh;
                                           QUERY PLAN                                            
-------------------------------------------------------------------------------------------------
 Sort  (cost=20070.93..20320.93 rows=100000 width=47)
   Output: dw.dwmc, dw.dwbh, dw.dwdz, gr.grbh, gr.xm, jf.ny, jf.je
   Sort Key: dw.dwbh
   ->  Hash Join  (cost=3754.00..8689.61 rows=100000 width=47)
         Output: dw.dwmc, dw.dwbh, dw.dwdz, gr.grbh, gr.xm, jf.ny, jf.je
         Inner Unique: true
         Hash Cond: ((gr.dwbh)::text = (dw.dwbh)::text)
         ->  Hash Join  (cost=3465.00..8138.00 rows=100000 width=31)
               Output: gr.grbh, gr.xm, gr.dwbh, jf.ny, jf.je
               Hash Cond: ((jf.grbh)::text = (gr.grbh)::text)
               ->  Seq Scan on public.t_jfxx jf  (cost=0.00..1637.00 rows=100000 width=20)
                     Output: jf.ny, jf.je, jf.grbh
               ->  Hash  (cost=1726.00..1726.00 rows=100000 width=16)
                     Output: gr.grbh, gr.xm, gr.dwbh
                     ->  Seq Scan on public.t_grxx gr  (cost=0.00..1726.00 rows=100000 width=16)
                           Output: gr.grbh, gr.xm, gr.dwbh
         ->  Hash  (cost=164.00..164.00 rows=10000 width=20)
               Output: dw.dwmc, dw.dwbh, dw.dwdz
               ->  Seq Scan on public.t_dwxx dw  (cost=0.00..164.00 rows=10000 width=20)
                     Output: dw.dwmc, dw.dwbh, dw.dwdz
(20 rows)

启动gdb,设置断点跟踪

(gdb) b hash_inner_and_outer
Breakpoint 1 at 0x7b066b: file joinpath.c, line 1684.
(gdb) c
Continuing.

Breakpoint 1, hash_inner_and_outer (root=0x2676078, joinrel=0x26d2bc0, outerrel=0x26814e0, innerrel=0x2682a10, 
    jointype=JOIN_INNER, extra=0x7ffd6ea6b9d0) at joinpath.c:1684
1684        JoinType    save_jointype = jointype;

连接类型为JOIN_INNER

(gdb) p jointype
$1 = JOIN_INNER

1号和3号RTE的连接(即t_dwxx和t_grxx)

(gdb) p *joinrel->relids->words
$3 = 10

开始遍历连接条件,获取hash连接条件

1697        foreach(l, extra->restrictlist)
(gdb) 
1699            RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(l);

成功获取,t_dwxx.dwbh = t_grxx.dwbh

(gdb) 
1697        foreach(l, extra->restrictlist)
(gdb) 
1722        if (hashclauses)
(gdb) p *hashclauses
$4 = {type = T_List, length = 1, head = 0x26d4068, tail = 0x26d4068}

获取成本最低的外表启动路径/成本最低的外表访问路径/成本最低的内部访问路径
分别是外表顺序扫描/外表顺序扫描/内部顺序扫描

(gdb) n
1729            Path       *cheapest_startup_outer = outerrel->cheapest_startup_path;
(gdb) 
1730            Path       *cheapest_total_outer = outerrel->cheapest_total_path;
(gdb) 
1731            Path       *cheapest_total_inner = innerrel->cheapest_total_path;
(gdb) p *cheapest_startup_outer
$5 = {type = T_Path, pathtype = T_SeqScan, parent = 0x26814e0, pathtarget = 0x2681718, param_info = 0x0, 
  parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 10000, startup_cost = 0, total_cost = 164, 
  pathkeys = 0x0}
(gdb) p *cheapest_total_outer
$6 = {type = T_Path, pathtype = T_SeqScan, parent = 0x26814e0, pathtarget = 0x2681718, param_info = 0x0, 
  parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 10000, startup_cost = 0, total_cost = 164, 
  pathkeys = 0x0}
(gdb) p *cheapest_total_inner
$7 = {type = T_Path, pathtype = T_SeqScan, parent = 0x2682a10, pathtarget = 0x2682c48, param_info = 0x0, 
  parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 100000, startup_cost = 0, total_cost = 1726, 
  pathkeys = 0x0}

如外表成本最低的启动路径不为NULL,则尝试hash连接

(gdb) n
1740                PATH_PARAM_BY_REL(cheapest_total_inner, outerrel))
(gdb) 
1739            if (PATH_PARAM_BY_REL(cheapest_total_outer, innerrel) ||
(gdb) 
1744            if (jointype == JOIN_UNIQUE_OUTER)
(gdb) 
1760            else if (jointype == JOIN_UNIQUE_INNER)
(gdb) 
1796                if (cheapest_startup_outer != NULL)
(gdb) 
1797                    try_hashjoin_path(root,

进入try_hashjoin_path

(gdb) step
try_hashjoin_path (root=0x2676078, joinrel=0x26d2bc0, outer_path=0x26853b8, inner_path=0x26cf610, hashclauses=0x26d4090, 
    jointype=JOIN_INNER, extra=0x7ffd6ea6b9d0) at joinpath.c:737
737     required_outer = calc_non_nestloop_required_outer(outer_path,

try_hashjoin_path->初步估算成本

...
751     initial_cost_hashjoin(root, &workspace, jointype, hashclauses,
(gdb) p workspace
$9 = {startup_cost = 3465, total_cost = 4261, run_cost = 796, inner_run_cost = 0, 
  inner_rescan_run_cost = 6.9528109284473596e-310, outer_rows = 3.7882102964330281e-317, 
  inner_rows = 2.0115578425988515e-316, outer_skip_rows = 2.0115578425988515e-316, 
  inner_skip_rows = 6.9528109284331305e-310, numbuckets = 131072, numbatches = 2, inner_rows_total = 100000}    

try_hashjoin_path->进入函数create_hashjoin_path

(gdb) n
759                  create_hashjoin_path(root,
(gdb) step
create_hashjoin_path (root=0x2676078, joinrel=0x26d2bc0, jointype=JOIN_INNER, workspace=0x7ffd6ea6b850, 
    extra=0x7ffd6ea6b9d0, outer_path=0x26853b8, inner_path=0x26cf610, parallel_hash=false, restrict_clauses=0x26d3098, 
    required_outer=0x0, hashclauses=0x26d4090) at pathnode.c:2330
2330        HashPath   *pathnode = makeNode(HashPath);

try_hashjoin_path->create_hashjoin_path->计算成本并返回

(gdb) 
2370        final_cost_hashjoin(root, pathnode, workspace, extra);
(gdb) 
2372        return pathnode;
(gdb) 
2373    }
(gdb) p *pathnode
$10 = {jpath = {path = {type = T_HashPath, pathtype = T_HashJoin, parent = 0x26d2bc0, pathtarget = 0x26d2df8, 
      param_info = 0x0, parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 100000, 
      startup_cost = 3465, total_cost = 5386, pathkeys = 0x0}, jointype = JOIN_INNER, inner_unique = false, 
    outerjoinpath = 0x26853b8, innerjoinpath = 0x26cf610, joinrestrictinfo = 0x26d3098}, path_hashclauses = 0x26d4090, 
  num_batches = 2, inner_rows_total = 100000}

try_hashjoin_path->添加路径

(gdb) n
try_hashjoin_path (root=0x2676078, joinrel=0x26d2bc0, outer_path=0x26853b8, inner_path=0x26cf610, hashclauses=0x26d4090, 
    jointype=JOIN_INNER, extra=0x7ffd6ea6b9d0) at joinpath.c:758
758         add_path(joinrel, (Path *)
(gdb) 
776 }
(gdb) 

回到hash_inner_and_outer,继续循环

(gdb) 
hash_inner_and_outer (root=0x2676078, joinrel=0x26d2bc0, outerrel=0x26814e0, innerrel=0x2682a10, jointype=JOIN_INNER, 
    extra=0x7ffd6ea6b9d0) at joinpath.c:1805
1805                foreach(lc1, outerrel->cheapest_parameterized_paths)

结束函数调用

1904    }
(gdb) 
add_paths_to_joinrel (root=0x2676078, joinrel=0x26d2bc0, outerrel=0x26814e0, innerrel=0x2682a10, jointype=JOIN_INNER, 
    sjinfo=0x7ffd6ea6bac0, restrictlist=0x26d3098) at joinpath.c:315
315     if (joinrel->fdwroutine &&
(gdb) p *joinrel->pathlist
$11 = {type = T_List, length = 2, head = 0x26d4160, tail = 0x26d3e30}

查看joinrel的路径链表

(gdb) p *(Node *)joinrel->pathlist->head->data.ptr_value
$12 = {type = T_HashPath}
(gdb) p *(Node *)joinrel->pathlist->head->next->data.ptr_value
$13 = {type = T_MergePath}
(gdb) p *(HashPath *)joinrel->pathlist->head->data.ptr_value
$14 = {jpath = {path = {type = T_HashPath, pathtype = T_HashJoin, parent = 0x26d2bc0, pathtarget = 0x26d2df8, 
      param_info = 0x0, parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 100000, 
      startup_cost = 3465, total_cost = 5386, pathkeys = 0x0}, jointype = JOIN_INNER, inner_unique = false, 
    outerjoinpath = 0x26853b8, innerjoinpath = 0x26cf610, joinrestrictinfo = 0x26d3098}, path_hashclauses = 0x26d4090, 
  num_batches = 2, inner_rows_total = 100000}
(gdb) p *(MergePath *)joinrel->pathlist->head->next->data.ptr_value
$15 = {jpath = {path = {type = T_MergePath, pathtype = T_MergeJoin, parent = 0x26d2bc0, pathtarget = 0x26d2df8, 
      param_info = 0x0, parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 100000, 
      startup_cost = 10035.66023721841, total_cost = 11955.396048959938, pathkeys = 0x2685928}, jointype = JOIN_INNER, 
    inner_unique = false, outerjoinpath = 0x26ce070, innerjoinpath = 0x26cf610, joinrestrictinfo = 0x26d3098}, 
  path_mergeclauses = 0x26d3eb8, outersortkeys = 0x0, innersortkeys = 0x26d3f18, skip_mark_restore = false, 
  materialize_inner = false}

DONE!
函数initial_cost_hashjoin和final_cost_hashjoin在下一小节介绍.

四、参考资料

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

来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/6906/viewspace-2374828/,如需转载,请注明出处,否则将追究法律责任。

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