PostgreSQL中create_plan的实现逻辑是什么

本篇内容主要讲解"PostgreSQL中create_plan的实现逻辑是什么"，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习"PostgreSQL中create_plan的实现逻辑是什么"吧!

一、数据结构

Plan
所有计划节点通过将Plan结构作为第一个字段从Plan结构"派生"。这确保了在将节点转换为计划节点时，一切都能正常工作。(在执行器中以通用方式传递时，节点指针经常被转换为Plan *)

/* ---------------- *      Plan node * * All plan nodes "derive" from the Plan structure by having the * Plan structure as the first field.  This ensures that everything works * when nodes are cast to Plan's.  (node pointers are frequently cast to Plan* * when passed around generically in the executor) * 所有计划节点通过将Plan结构作为第一个字段从Plan结构"派生"。 * 这确保了在将节点转换为计划节点时，一切都能正常工作。 * (在执行器中以通用方式传递时，节点指针经常被转换为Plan *) * * We never actually instantiate any Plan nodes; this is just the common * abstract superclass for all Plan-type nodes. * 从未实例化任何Plan节点;这只是所有Plan-type节点的通用抽象超类。 * ---------------- */typedef struct Plan{    NodeTag     type;//节点类型    /*     * 成本估算信息;estimated execution costs for plan (see costsize.c for more info)     */    Cost        startup_cost;   /* 启动成本;cost expended before fetching any tuples */    Cost        total_cost;     /* 总成本;total cost (assuming all tuples fetched) */    /*     * 优化器估算信息;planner's estimate of result size of this plan step     */    double      plan_rows;      /* 行数;number of rows plan is expected to emit */    int         plan_width;     /* 平均行大小(Byte为单位);average row width in bytes */    /*     * 并行执行相关的信息;information needed for parallel query     */    bool        parallel_aware; /* 是否参与并行执行逻辑?engage parallel-aware logic? */    bool        parallel_safe;  /* 是否并行安全;OK to use as part of parallel plan? */    /*     * Plan类型节点通用的信息.Common structural data for all Plan types.     */    int         plan_node_id;   /* unique across entire final plan tree */    List       *targetlist;     /* target list to be computed at this node */    List       *qual;           /* implicitly-ANDed qual conditions */    struct Plan *lefttree;      /* input plan tree(s) */    struct Plan *righttree;    List       *initPlan;       /* Init Plan nodes (un-correlated expr                                 * subselects) */    /*     * Information for management of parameter-change-driven rescanning     * parameter-change-driven重扫描的管理信息.     *      * extParam includes the paramIDs of all external PARAM_EXEC params     * affecting this plan node or its children.  setParam params from the     * node's initPlans are not included, but their extParams are.     *     * allParam includes all the extParam paramIDs, plus the IDs of local     * params that affect the node (i.e., the setParams of its initplans).     * These are _all_ the PARAM_EXEC params that affect this node.     */    Bitmapset  *extParam;    Bitmapset  *allParam;} Plan;

二、源码解读

create_plan调用create_plan_recurse函数，递归遍历访问路径，相应的创建计划（Plan）节点。

/* * create_plan *    Creates the access plan for a query by recursively processing the *    desired tree of pathnodes, starting at the node 'best_path'.  For *    every pathnode found, we create a corresponding plan node containing *    appropriate id, target list, and qualification information. *    从节点'best_path'开始,递归处理路径节点树，为查询语句创建执行计划。 *    对于找到的每个访问路径节点，创建一个相应的计划节点，其中包含合适的id、投影列和限定信息。 * *    The tlists and quals in the plan tree are still in planner format, *    ie, Vars still correspond to the parser's numbering.  This will be *    fixed later by setrefs.c. *    计划中的投影列和约束条件仍然以优化器的格式存储. *    比如Vars对应着解析树的编号等,这些处理都在setrefs.c中完成 * *    best_path is the best access path *    best_path是最优的访问路径 * *    Returns a Plan tree. *    返回Plan树. */Plan *create_plan(PlannerInfo *root, Path *best_path){    Plan       *plan;    /* plan_params should not be in use in current query level */    //plan_params在当前查询层次上不应使用(值为NULL)    Assert(root->plan_params == NIL);    /* Initialize this module's private workspace in PlannerInfo */    //初始化该模块中优化器信息的私有工作空间    root->curOuterRels = NULL;    root->curOuterParams = NIL;    /* Recursively process the path tree, demanding the correct tlist result */    //递归处理计划树(tlist参数设置为CP_EXACT_TLIST)    plan = create_plan_recurse(root, best_path, CP_EXACT_TLIST);    /*     * Make sure the topmost plan node's targetlist exposes the original     * column names and other decorative info.  Targetlists generated within     * the planner don't bother with that stuff, but we must have it on the     * top-level tlist seen at execution time.  However, ModifyTable plan     * nodes don't have a tlist matching the querytree targetlist.     * 确保最顶层计划节点的投影列targetlist可以获知原始列名和其他调整过的信息。     * 在计划器中生成的投影列targetlist不需要处理这些信息，但是必须在执行时看到最高层的投影列tlist。     * 注意:ModifyTable计划节点没有一个匹配查询树targetlist的tlist。     */    if (!IsA(plan, ModifyTable))        apply_tlist_labeling(plan->targetlist, root->processed_tlist);//非ModifyTable    /*     * Attach any initPlans created in this query level to the topmost plan     * node.  (In principle the initplans could go in any plan node at or     * above where they're referenced, but there seems no reason to put them     * any lower than the topmost node for the query level.  Also, see     * comments for SS_finalize_plan before you try to change this.)     * 将此查询级别中创建的任何initplan附加到最高层的计划节点中。     * (原则上，initplans可以在引用它们的任何计划节点或以上的节点中访问，     * 但似乎没有理由将它们放在查询级别的最高层节点以下。     * 另外，如需尝试更改SS_finalize_plan,请参阅注释。)     */    SS_attach_initplans(root, plan);    /* Check we successfully assigned all NestLoopParams to plan nodes */    //检查已经为计划节点参数NestLoopParams赋值    if (root->curOuterParams != NIL)        elog(ERROR, "failed to assign all NestLoopParams to plan nodes");    /*     * Reset plan_params to ensure param IDs used for nestloop params are not     * re-used later     * 重置plan_params参数,以确保用于nestloop参数的参数IDs不会在后续被重复使用     */    root->plan_params = NIL;    return plan;}//------------------------------------------------------------------------ create_plan_recurse/* * create_plan_recurse *    Recursive guts of create_plan(). *    create_plan()函数中的递归实现过程. */static Plan *create_plan_recurse(PlannerInfo *root, Path *best_path, int flags){    Plan       *plan;    /* Guard against stack overflow due to overly complex plans */    //确保堆栈不会溢出    check_stack_depth();    switch (best_path->pathtype)//根据路径类型,执行相应的处理    {        case T_SeqScan://顺序扫描        case T_SampleScan://采样扫描        case T_IndexScan://索引扫描        case T_IndexOnlyScan://索引快速扫描        case T_BitmapHeapScan://位图堆扫描        case T_TidScan://TID扫描        case T_SubqueryScan://子查询扫描        case T_FunctionScan://函数扫描        case T_TableFuncScan://表函数扫描        case T_ValuesScan://Values扫描        case T_CteScan://CTE扫描        case T_WorkTableScan://WorkTable扫描        case T_NamedTuplestoreScan://NamedTuplestore扫描        case T_ForeignScan://外表扫描        case T_CustomScan://自定义扫描            plan = create_scan_plan(root, best_path, flags);//扫描计划            break;        case T_HashJoin://Hash连接        case T_MergeJoin://合并连接        case T_NestLoop://内嵌循环连接            plan = create_join_plan(root,                                    (JoinPath *) best_path);//连接结合            break;        case T_Append://追加(集合)            plan = create_append_plan(root,                                      (AppendPath *) best_path);//追加(集合并)计划            break;        case T_MergeAppend://合并            plan = create_merge_append_plan(root,                                            (MergeAppendPath *) best_path);            break;        case T_Result://投影操作            if (IsA(best_path, ProjectionPath))            {                plan = create_projection_plan(root,                                              (ProjectionPath *) best_path,                                              flags);            }            else if (IsA(best_path, MinMaxAggPath))            {                plan = (Plan *) create_minmaxagg_plan(root,                                                      (MinMaxAggPath *) best_path);            }            else            {                Assert(IsA(best_path, ResultPath));                plan = (Plan *) create_result_plan(root,                                                   (ResultPath *) best_path);            }            break;        case T_ProjectSet://投影集合操作            plan = (Plan *) create_project_set_plan(root,                                                    (ProjectSetPath *) best_path);            break;        case T_Material://物化            plan = (Plan *) create_material_plan(root,                                                 (MaterialPath *) best_path,                                                 flags);            break;        case T_Unique://唯一处理            if (IsA(best_path, UpperUniquePath))            {                plan = (Plan *) create_upper_unique_plan(root,                                                         (UpperUniquePath *) best_path,                                                         flags);            }            else            {                Assert(IsA(best_path, UniquePath));                plan = create_unique_plan(root,                                          (UniquePath *) best_path,                                          flags);            }            break;        case T_Gather://汇总收集            plan = (Plan *) create_gather_plan(root,                                               (GatherPath *) best_path);            break;        case T_Sort://排序            plan = (Plan *) create_sort_plan(root,                                             (SortPath *) best_path,                                             flags);            break;        case T_Group://分组            plan = (Plan *) create_group_plan(root,                                              (GroupPath *) best_path);            break;        case T_Agg://聚集计算            if (IsA(best_path, GroupingSetsPath))                plan = create_groupingsets_plan(root,                                                (GroupingSetsPath *) best_path);            else            {                Assert(IsA(best_path, AggPath));                plan = (Plan *) create_agg_plan(root,                                                (AggPath *) best_path);            }            break;        case T_WindowAgg://窗口函数            plan = (Plan *) create_windowagg_plan(root,                                                  (WindowAggPath *) best_path);            break;        case T_SetOp://集合操作            plan = (Plan *) create_setop_plan(root,                                              (SetOpPath *) best_path,                                              flags);            break;        case T_RecursiveUnion://递归UNION            plan = (Plan *) create_recursiveunion_plan(root,                                                       (RecursiveUnionPath *) best_path);            break;        case T_LockRows://锁定(for update)            plan = (Plan *) create_lockrows_plan(root,                                                 (LockRowsPath *) best_path,                                                 flags);            break;        case T_ModifyTable://更新            plan = (Plan *) create_modifytable_plan(root,                                                    (ModifyTablePath *) best_path);            break;        case T_Limit://限制操作            plan = (Plan *) create_limit_plan(root,                                              (LimitPath *) best_path,                                              flags);            break;        case T_GatherMerge://收集合并            plan = (Plan *) create_gather_merge_plan(root,                                                     (GatherMergePath *) best_path);            break;        default://其他非法类型            elog(ERROR, "unrecognized node type: %d",                 (int) best_path->pathtype);            plan = NULL;        /* keep compiler quiet */            break;    }    return plan;}//------------------------------------------------------------------------ apply_tlist_labeling /*  * apply_tlist_labeling  *      Apply the TargetEntry labeling attributes of src_tlist to dest_tlist  *      将src_tlist的TargetEntry标记属性应用到dest_tlist  *  * This is useful for reattaching column names etc to a plan's final output  * targetlist.  */ void apply_tlist_labeling(List *dest_tlist, List *src_tlist) {     ListCell   *ld,                *ls;      Assert(list_length(dest_tlist) == list_length(src_tlist));     forboth(ld, dest_tlist, ls, src_tlist)     {         TargetEntry *dest_tle = (TargetEntry *) lfirst(ld);         TargetEntry *src_tle = (TargetEntry *) lfirst(ls);          Assert(dest_tle->resno == src_tle->resno);         dest_tle->resname = src_tle->resname;         dest_tle->ressortgroupref = src_tle->ressortgroupref;         dest_tle->resorigtbl = src_tle->resorigtbl;         dest_tle->resorigcol = src_tle->resorigcol;         dest_tle->resjunk = src_tle->resjunk;     } } //------------------------------------------------------------------------ apply_tlist_labeling /*  * SS_attach_initplans - attach initplans to topmost plan node  * 将initplans附加到最顶层的计划节点   *  * Attach any initplans created in the current query level to the specified  * plan node, which should normally be the topmost node for the query level.  * (In principle the initPlans could go in any node at or above where they're  * referenced; but there seems no reason to put them any lower than the  * topmost node, so we don't bother to track exactly where they came from.)  * We do not touch the plan node's cost; the initplans should have been  * accounted for in path costing.  */ void SS_attach_initplans(PlannerInfo *root, Plan *plan) {     plan->initPlan = root->init_plans; }

三、跟踪分析

测试脚本如下

testdb=# explain 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) grjftestdb-# order by dw.dwbh;                                        QUERY PLAN                                        ------------------------------------------------------------------------------------------ Sort  (cost=20070.93..20320.93 rows=100000 width=47)   Sort Key: dw.dwbh   ->  Hash Join  (cost=3754.00..8689.61 rows=100000 width=47)         Hash Cond: ((gr.dwbh)::text = (dw.dwbh)::text)         ->  Hash Join  (cost=3465.00..8138.00 rows=100000 width=31)               Hash Cond: ((jf.grbh)::text = (gr.grbh)::text)               ->  Seq Scan on t_jfxx jf  (cost=0.00..1637.00 rows=100000 width=20)               ->  Hash  (cost=1726.00..1726.00 rows=100000 width=16)                     ->  Seq Scan on t_grxx gr  (cost=0.00..1726.00 rows=100000 width=16)         ->  Hash  (cost=164.00..164.00 rows=10000 width=20)               ->  Seq Scan on t_dwxx dw  (cost=0.00..164.00 rows=10000 width=20)(11 rows)

启动gdb,设置断点,进入

(gdb) info breakNum     Type           Disp Enb Address            What2       breakpoint     keep y   0x00000000007b76c1 in create_plan at createplan.c:313(gdb) cContinuing.Breakpoint 2, create_plan (root=0x26c1258, best_path=0x2722d00) at createplan.c:313313     Assert(root->plan_params == NIL);

进入create_plan_recurse函数

313     Assert(root->plan_params == NIL);(gdb) n316     root->curOuterRels = NULL;(gdb) 317     root->curOuterParams = NIL;(gdb) 320     plan = create_plan_recurse(root, best_path, CP_EXACT_TLIST);(gdb) stepcreate_plan_recurse (root=0x26c1258, best_path=0x2722d00, flags=1) at createplan.c:364364     check_stack_depth();

根据访问路径类型(T_ProjectionPath)选择处理分支

(gdb) p *best_path$1 = {type = T_ProjectionPath, pathtype = T_Result, parent = 0x2722998, pathtarget = 0x27226f8, param_info = 0x0,   parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 100000, startup_cost = 20070.931487218411,   total_cost = 20320.931487218411, pathkeys = 0x26cfe98}

调用create_projection_plan函数

(gdb) n400             if (IsA(best_path, ProjectionPath))(gdb) 402                 plan = create_projection_plan(root,

创建相应的Plan(T_Sort,存在左右子树),下一节将详细解释create_projection_plan函数

(gdb) 504     return plan;(gdb) p *plan$1 = {type = T_Sort, startup_cost = 20070.931487218411, total_cost = 20320.931487218411, plan_rows = 100000,   plan_width = 47, parallel_aware = false, parallel_safe = true, plan_node_id = 0, targetlist = 0x2724548, qual = 0x0,   lefttree = 0x27243d0, righttree = 0x0, initPlan = 0x0, extParam = 0x0, allParam = 0x0}

执行返回

(gdb) create_plan (root=0x270f9c8, best_path=0x2722d00) at createplan.c:329329     if (!IsA(plan, ModifyTable))(gdb) 330         apply_tlist_labeling(plan->targetlist, root->processed_tlist);(gdb) 339     SS_attach_initplans(root, plan);(gdb) 342     if (root->curOuterParams != NIL)(gdb) 349     root->plan_params = NIL;(gdb) 351     return plan;

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