PostgreSQL中hash_inner_and_outer函数分析

这篇文章主要讲解了“postgresql中hash_inner_and_outer函数分析”，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习“Postgresql中hash_inner_and_outer函数分析”吧！

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; 

 
 
 
 
 #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    

 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


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;

    
    hashclauses = NIL;
    foreach(l, extra->restrictlist)
    {
        RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(l);

        
        if (isouterjoin && RINFO_IS_PUSHED_DOWN(restrictinfo, joinrel->relids))
            continue;

        if (!restrictinfo->can_join ||
            restrictinfo->hashjoinoperator == InvalidOid)
            continue;           

        
        if (!clause_sides_match_join(restrictinfo, outerrel, innerrel))
            continue;           

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

    
    //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)
    {
        
        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 (PATH_PARAM_BY_REL(cheapest_total_outer, innerrel) ||
            PATH_PARAM_BY_REL(cheapest_total_inner, outerrel))
            return;//直接退出

        
        //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);
            
        }
        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
        {
            
            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);

                
                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);

                    
                    if (PATH_PARAM_BY_REL(innerpath, outerrel))
                        continue;

                    if (outerpath == cheapest_startup_outer &&
                        innerpath == cheapest_total_inner)
                        continue;   

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

        
        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);

            
            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  );
            }

            
            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  );
        }
    }
}
 

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

 
 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;
 
     
     required_outer = calc_non_nestloop_required_outer(outer_path,
                                                       inner_path);
     if (required_outer &&
         !bms_overlap(required_outer, extra->param_source_rels))
     {
         
         bms_free(required_outer);
         return;
     }
 
     
     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,    
                                       extra->restrictlist,
                                       required_outer,
                                       hashclauses));//创建hash join访问路径,并添加
     }
     else
     {
         
         bms_free(required_outer);
     }
 }
 

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

 
 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;
     
     pathnode->jpath.path.parallel_workers = outer_path->parallel_workers;
 
     
     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(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}

感谢各位的阅读，以上就是“PostgreSQL中hash_inner_and_outer函数分析”的内容了，经过本文的学习后，相信大家对PostgreSQL中hash_inner_and_outer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。这里是编程网，小编将为大家推送更多相关知识点的文章，欢迎关注！