本节简单介绍了创建执行计划主函数create_plan的实现逻辑。
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) grjf
testdb-# 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 break
Num Type Disp Enb Address What
2 breakpoint keep y 0x00000000007b76c1 in create_plan at createplan.c:313
(gdb) c
Continuing.
Breakpoint 2, create_plan (root=0x26c1258, best_path=0x2722d00) at createplan.c:313
313 Assert(root->plan_params == NIL);
进入create_plan_recurse函数
313 Assert(root->plan_params == NIL);
(gdb) n
316 root->curOuterRels = NULL;
(gdb)
317 root->curOuterParams = NIL;
(gdb)
320 plan = create_plan_recurse(root, best_path, CP_EXACT_TLIST);
(gdb) step
create_plan_recurse (root=0x26c1258, best_path=0x2722d00, flags=1) at createplan.c:364
364 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) n
400 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:329
329 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;
DONE!
