这篇文章主要讲解了“PostgreSQL中create_sort_plan函数实现逻辑是什么”，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create_sort_plan函数实现逻辑是什么”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 *)
typedef struct Plan
{
NodeTag type;//节点类型
Cost startup_cost;
Cost total_cost;
double plan_rows;
int plan_width;
bool parallel_aware;
bool parallel_safe;
int plan_node_id;
List *targetlist;
List *qual;
struct Plan *lefttree;
struct Plan *righttree;
List *initPlan;
Bitmapset *extParam;
Bitmapset *allParam;
} Plan;二、源码解读
create_plan->create_plan_recurse->create_projection_plan函数创建计划树,执行投影操作并通过递归的方式为子访问路径生成执行计划。create_sort_plan函数创建Sort计划节点。
//---------------------------------------------------------------- create_projection_plan
static Plan *
create_projection_plan(PlannerInfo *root, ProjectionPath *best_path, int flags)
{
Plan *plan;
Plan *subplan;
List *tlist;
bool needs_result_node = false;
if (use_physical_tlist(root, &best_path->path, flags))
{
subplan = create_plan_recurse(root, best_path->subpath, 0);
tlist = subplan->targetlist;
if (flags & CP_LABEL_TLIST)
apply_pathtarget_labeling_to_tlist(tlist,
best_path->path.pathtarget);
}
else if (is_projection_capable_path(best_path->subpath))
{
subplan = create_plan_recurse(root, best_path->subpath,
CP_IGNORE_TLIST);
tlist = build_path_tlist(root, &best_path->path);
}
else
{
subplan = create_plan_recurse(root, best_path->subpath, 0);
tlist = build_path_tlist(root, &best_path->path);
needs_result_node = !tlist_same_exprs(tlist, subplan->targetlist);
}
if (!needs_result_node)
{
//不需要单独的Result节点,把tlist赋值给subplan
plan = subplan;
plan->targetlist = tlist;
//标记估算成本
plan->startup_cost = best_path->path.startup_cost;
plan->total_cost = best_path->path.total_cost;
plan->plan_rows = best_path->path.rows;
plan->plan_width = best_path->path.pathtarget->width;
plan->parallel_safe = best_path->path.parallel_safe;
}
else
{
//需要Result节点
plan = (Plan *) make_result(tlist, NULL, subplan);
copy_generic_path_info(plan, (Path *) best_path);
}
return plan;
}
//---------------------------------------------------------------- create_sort_plan
static Sort *
create_sort_plan(PlannerInfo *root, SortPath *best_path, int flags)
{
Sort *plan;
Plan *subplan;
subplan = create_plan_recurse(root, best_path->subpath,
flags | CP_SMALL_TLIST);
plan = make_sort_from_pathkeys(subplan, best_path->path.pathkeys,
IS_OTHER_REL(best_path->subpath->parent) ?
best_path->path.parent->relids : NULL);
copy_generic_path_info(&plan->plan, (Path *) best_path);
return plan;
}
//------------------------------------------------ build_path_tlist
static List *
build_path_tlist(PlannerInfo *root, Path *path)
{
List *tlist = NIL;
Index *sortgrouprefs = path->pathtarget->sortgrouprefs;
int resno = 1;
ListCell *v;
foreach(v, path->pathtarget->exprs)
{
Node *node = (Node *) lfirst(v);
TargetEntry *tle;
if (path->param_info)
node = replace_nestloop_params(root, node);
tle = makeTargetEntry((Expr *) node,
resno,
NULL,
false);
if (sortgrouprefs)
tle->ressortgroupref = sortgrouprefs[resno - 1];
tlist = lappend(tlist, tle);
resno++;
}
return tlist;
}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create_projection_plan函数
(gdb) b create_projection_plan
Breakpoint 2 at 0x7b95a8: file createplan.c, line 1627.
(gdb) c
Continuing.
Breakpoint 2, create_projection_plan (root=0x26c1258, best_path=0x2722d00, flags=1) at createplan.c:1627
1627 bool needs_result_node = false;转换subpath为Plan,并确定是否需要Result节点,并且判断是否需要生成Result节点
...
(gdb) n
1642 if (use_physical_tlist(root, &best_path->path, flags))
(gdb) n
1655 else if (is_projection_capable_path(best_path->subpath))
(gdb)
1673 subplan = create_plan_recurse(root, best_path->subpath, 0);查看best_path&best_path->subpath变量
(gdb) p *best_path
$3 = {path = {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}, subpath = 0x2722c68, dummypp = true}
(gdb) p *(SortPath *)best_path->subpath
$16 = {path = {type = T_SortPath, pathtype = T_Sort, parent = 0x2722998, pathtarget = 0x27212d8, param_info = 0x0,
parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 100000, startup_cost = 20070.931487218411,
total_cost = 20320.931487218411, pathkeys = 0x26cfe98}, subpath = 0x2721e60}创建subpath(SortPath)的执行计划
(gdb) step
create_plan_recurse (root=0x26c1258, best_path=0x2722c68, flags=0) at createplan.c:364
364 check_stack_depth();
(gdb) n
366 switch (best_path->pathtype)
(gdb)
447 plan = (Plan *) create_sort_plan(root,进入create_sort_plan
(gdb) step
create_sort_plan (root=0x26c1258, best_path=0x2722c68, flags=0) at createplan.c:1759
1759 subplan = create_plan_recurse(root, best_path->subpath,SortPath的subpath是HashPath
(gdb) p best_path->subpath->type
$17 = T_HashPath
(gdb) p *(HashPath *)best_path->subpath
$18 = {jpath = {path = {type = T_HashPath, pathtype = T_HashJoin, parent = 0x27210c0, pathtarget = 0x27212d8,
param_info = 0x0, parallel_aware = false, parallel_safe = true, parallel_workers = 0, rows = 100000,
startup_cost = 3754, total_cost = 8689.6112499999999, pathkeys = 0x0}, jointype = JOIN_INNER, inner_unique = true,
outerjoinpath = 0x2720f68, innerjoinpath = 0x26d0598, joinrestrictinfo = 0x2722068}, path_hashclauses = 0x27223c0,
num_batches = 1, inner_rows_total = 10000}完成SortPath执行计划的构建
(gdb)
1774 return plan;
(gdb)
1775 }
(gdb) p *plan
$20 = {plan = {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 = 0x2723208, qual = 0x0,
lefttree = 0x27243d0, righttree = 0x0, initPlan = 0x0, extParam = 0x0, allParam = 0x0}, numCols = 1,
sortColIdx = 0x27222a0, sortOperators = 0x2724468, collations = 0x2724488, nullsFirst = 0x27244a8}回到上一层
(gdb) n
create_plan_recurse (root=0x26c1258, best_path=0x2722c68, flags=0) at createplan.c:450
450 break;回到create_projection_plan函数
(gdb) n
504 return plan;
(gdb)
505 }
(gdb)
create_projection_plan (root=0x26c1258, best_path=0x2722d00, flags=1) at createplan.c:1674
1674 tlist = build_path_tlist(root, &best_path->path);执行完毕,返回create_plan,结果,最外层的Plan为Sort
(gdb)
1708 return plan;
(gdb)
1709 }
(gdb) p *plan
$22 = {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}
(gdb) n
create_plan_recurse (root=0x26c1258, best_path=0x2722d00, flags=1) at createplan.c:504
504 return plan;
(gdb) p *plan
$23 = {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}
(gdb) n
505 }
(gdb)
create_plan (root=0x26c1258, best_path=0x2722d00) at createplan.c:329
329 if (!IsA(plan, ModifyTable))感谢各位的阅读，以上就是“PostgreSQL中create_sort_plan函数实现逻辑是什么”的内容了，经过本文的学习后，相信大家对PostgreSQL中create_sort_plan函数实现逻辑是什么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。这里是亿速云，小编将为大家推送更多相关知识点的文章，欢迎关注！
