PostgreSQL 源码解读（79）- 查询语句#64（create_plan函数#3-Se...
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本节介绍了创建计划create_plan函数中扫描计划的实现过程，主要的逻辑在函数create_scan_plan中实现。
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_scan_plan函数创建Scan Plan.扫描可以分为顺序扫描(全表扫描)/索引扫描/索引快速扫描/TID扫描等多种扫描方式,这里主要介绍常见的顺序扫描和索引扫描,相应的实现函数是create_seqscan_plan和create_indexscan_plan.
//--------------------------------------------------- create_scan_plan
static Plan *
create_scan_plan(PlannerInfo *root, Path *best_path, int flags)
{
RelOptInfo *rel = best_path->parent;
List *scan_clauses;
List *gating_clauses;
List *tlist;
Plan *plan;
switch (best_path->pathtype)
{
case T_IndexScan:
case T_IndexOnlyScan://索引扫描,使用索引约束条件
scan_clauses = castNode(IndexPath, best_path)->indexinfo->indrestrictinfo;
break;
default:
scan_clauses = rel->baserestrictinfo;//默认使用关系中的约束条件
break;
}
if (best_path->param_info)
scan_clauses = list_concat(list_copy(scan_clauses),
best_path->param_info->ppi_clauses);
gating_clauses = get_gating_quals(root, scan_clauses);
if (gating_clauses)
flags = 0;
if (flags == CP_IGNORE_TLIST)
{
tlist = NULL;//使用CP_IGNORE_TLIST标志,则设置tlist为NULL
}
else if (use_physical_tlist(root, best_path, flags))
{
if (best_path->pathtype == T_IndexOnlyScan)//索引快速扫描
{
//对于所有快速扫描,tlist中的列应在索引中
tlist = copyObject(((IndexPath *) best_path)->indexinfo->indextlist);
if (flags & CP_LABEL_TLIST)
apply_pathtarget_labeling_to_tlist(tlist, best_path->pathtarget);
}
else//非索引快速扫描
{
tlist = build_physical_tlist(root, rel);//构建物理的tlist
if (tlist == NIL)
{
//build_physical_tlist无法构建,则使用常规方法构建
tlist = build_path_tlist(root, best_path);
}
else
{
if (flags & CP_LABEL_TLIST)
apply_pathtarget_labeling_to_tlist(tlist, best_path->pathtarget);
}
}
}
else
{
tlist = build_path_tlist(root, best_path);//使用常规方法构建
}
switch (best_path->pathtype)//根据路径类型进行相应的处理
{
case T_SeqScan://顺序扫描
plan = (Plan *) create_seqscan_plan(root,
best_path,
tlist,
scan_clauses);
break;
case T_SampleScan:
plan = (Plan *) create_samplescan_plan(root,
best_path,
tlist,
scan_clauses);
break;
case T_IndexScan:
plan = (Plan *) create_indexscan_plan(root,
(IndexPath *) best_path,
tlist,
scan_clauses,
false);
break;
case T_IndexOnlyScan:
plan = (Plan *) create_indexscan_plan(root,
(IndexPath *) best_path,
tlist,
scan_clauses,
true);
break;
case T_BitmapHeapScan:
plan = (Plan *) create_bitmap_scan_plan(root,
(BitmapHeapPath *) best_path,
tlist,
scan_clauses);
break;
case T_TidScan:
plan = (Plan *) create_tidscan_plan(root,
(TidPath *) best_path,
tlist,
scan_clauses);
break;
case T_SubqueryScan:
plan = (Plan *) create_subqueryscan_plan(root,
(SubqueryScanPath *) best_path,
tlist,
scan_clauses);
break;
case T_FunctionScan:
plan = (Plan *) create_functionscan_plan(root,
best_path,
tlist,
scan_clauses);
break;
case T_TableFuncScan:
plan = (Plan *) create_tablefuncscan_plan(root,
best_path,
tlist,
scan_clauses);
break;
case T_ValuesScan:
plan = (Plan *) create_valuesscan_plan(root,
best_path,
tlist,
scan_clauses);
break;
case T_CteScan:
plan = (Plan *) create_ctescan_plan(root,
best_path,
tlist,
scan_clauses);
break;
case T_NamedTuplestoreScan:
plan = (Plan *) create_namedtuplestorescan_plan(root,
best_path,
tlist,
scan_clauses);
break;
case T_WorkTableScan:
plan = (Plan *) create_worktablescan_plan(root,
best_path,
tlist,
scan_clauses);
break;
case T_ForeignScan:
plan = (Plan *) create_foreignscan_plan(root,
(ForeignPath *) best_path,
tlist,
scan_clauses);
break;
case T_CustomScan:
plan = (Plan *) create_customscan_plan(root,
(CustomPath *) best_path,
tlist,
scan_clauses);
break;
default:
elog(ERROR, "unrecognized node type: %d",
(int) best_path->pathtype);
plan = NULL;
break;
}
if (gating_clauses)
plan = create_gating_plan(root, best_path, plan, gating_clauses);
return plan;
}
//------------------------------------- create_seqscan_plan
static SeqScan *
create_seqscan_plan(PlannerInfo *root, Path *best_path,
List *tlist, List *scan_clauses)
{
SeqScan *scan_plan;
Index scan_relid = best_path->parent->relid;
//基本关系
Assert(scan_relid > 0);
Assert(best_path->parent->rtekind == RTE_RELATION);
//约束条件排序为最佳的执行顺序
scan_clauses = order_qual_clauses(root, scan_clauses);
//规约限制条件信息链表到裸表达式,同时忽略pseudoconstants
scan_clauses = extract_actual_clauses(scan_clauses, false);
//参数化访问,则使用内嵌循环参数替换外表变量
if (best_path->param_info)
{
scan_clauses = (List *)
replace_nestloop_params(root, (Node *) scan_clauses);//约束条件
}
scan_plan = make_seqscan(tlist,
scan_clauses,
scan_relid);//构建扫描计划
copy_generic_path_info(&scan_plan->plan, best_path);
return scan_plan;//返回
}
//------------------------------------- copy_generic_path_info
static void
copy_generic_path_info(Plan *dest, Path *class="lazy" data-src)
{
dest->startup_cost = class="lazy" data-src->startup_cost;
dest->total_cost = class="lazy" data-src->total_cost;
dest->plan_rows = class="lazy" data-src->rows;
dest->plan_width = class="lazy" data-src->pathtarget->width;
dest->parallel_aware = class="lazy" data-src->parallel_aware;
dest->parallel_safe = class="lazy" data-src->parallel_safe;
}
//------------------------------------- make_seqscan
static SeqScan *
make_seqscan(List *qptlist,
List *qpqual,
Index scanrelid)
{
SeqScan *node = makeNode(SeqScan);
Plan *plan = &node->plan;
plan->targetlist = qptlist;
plan->qual = qpqual;
plan->lefttree = NULL;
plan->righttree = NULL;
node->scanrelid = scanrelid;
return node;//创建节点
}
//------------------------------------- create_indexscan_plan
static Scan *
create_indexscan_plan(PlannerInfo *root,
IndexPath *best_path,
List *tlist,
List *scan_clauses,
bool indexonly)
{
Scan *scan_plan;
List *indexquals = best_path->indexquals;
List *indexorderbys = best_path->indexorderbys;
Index baserelid = best_path->path.parent->relid;
Oid indexoid = best_path->indexinfo->indexoid;
List *qpqual;
List *stripped_indexquals;
List *fixed_indexquals;
List *fixed_indexorderbys;
List *indexorderbyops = NIL;
ListCell *l;
//基本关系
Assert(baserelid > 0);
Assert(best_path->path.parent->rtekind == RTE_RELATION);
stripped_indexquals = get_actual_clauses(indexquals);
fixed_indexquals = fix_indexqual_references(root, best_path);
fixed_indexorderbys = fix_indexorderby_references(root, best_path);
qpqual = NIL;
foreach(l, scan_clauses)//遍历scan_clauses链表
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, l);
if (rinfo->pseudoconstant)
continue;
if (list_member_ptr(indexquals, rinfo))
continue;
if (is_redundant_derived_clause(rinfo, indexquals))
continue;
if (!contain_mutable_functions((Node *) rinfo->clause) &&
predicate_implied_by(list_make1(rinfo->clause), indexquals, false))
continue;
qpqual = lappend(qpqual, rinfo);
}
//条件排序
qpqual = order_qual_clauses(root, qpqual);
//规约
qpqual = extract_actual_clauses(qpqual, false);
if (best_path->path.param_info)//存在参数信息,使用内嵌循环参数替换
{
stripped_indexquals = (List *)
replace_nestloop_params(root, (Node *) stripped_indexquals);
qpqual = (List *)
replace_nestloop_params(root, (Node *) qpqual);
indexorderbys = (List *)
replace_nestloop_params(root, (Node *) indexorderbys);
}
if (indexorderbys)
{
ListCell *pathkeyCell,
*exprCell;
Assert(list_length(best_path->path.pathkeys) == list_length(indexorderbys));
forboth(pathkeyCell, best_path->path.pathkeys, exprCell, indexorderbys)
{
PathKey *pathkey = (PathKey *) lfirst(pathkeyCell);
Node *expr = (Node *) lfirst(exprCell);
Oid exprtype = exprType(expr);
Oid sortop;
sortop = get_opfamily_member(pathkey->pk_opfamily,
exprtype,
exprtype,
pathkey->pk_strategy);
if (!OidIsValid(sortop))
elog(ERROR, "missing operator %d(%u,%u) in opfamily %u",
pathkey->pk_strategy, exprtype, exprtype, pathkey->pk_opfamily);
indexorderbyops = lappend_oid(indexorderbyops, sortop);
}
}
//OK,下面可以构建计划节点了
if (indexonly)
scan_plan = (Scan *) make_indexonlyscan(tlist,
qpqual,
baserelid,
indexoid,
fixed_indexquals,
fixed_indexorderbys,
best_path->indexinfo->indextlist,
best_path->indexscandir);
else
scan_plan = (Scan *) make_indexscan(tlist,
qpqual,
baserelid,
indexoid,
fixed_indexquals,
stripped_indexquals,
fixed_indexorderbys,
indexorderbys,
indexorderbyops,
best_path->indexscandir);
copy_generic_path_info(&scan_plan->plan, &best_path->path);
return scan_plan;
}
//------------------------------------- make_indexscan/make_indexonlyscan
static IndexScan *
make_indexscan(List *qptlist,
List *qpqual,
Index scanrelid,
Oid indexid,
List *indexqual,
List *indexqualorig,
List *indexorderby,
List *indexorderbyorig,
List *indexorderbyops,
ScanDirection indexscandir)
{
IndexScan *node = makeNode(IndexScan);
Plan *plan = &node->scan.plan;
plan->targetlist = qptlist;
plan->qual = qpqual;
plan->lefttree = NULL;
plan->righttree = NULL;
node->scan.scanrelid = scanrelid;
node->indexid = indexid;
node->indexqual = indexqual;
node->indexqualorig = indexqualorig;
node->indexorderby = indexorderby;
node->indexorderbyorig = indexorderbyorig;
node->indexorderbyops = indexorderbyops;
node->indexorderdir = indexscandir;
return node;
}
static IndexOnlyScan *
make_indexonlyscan(List *qptlist,
List *qpqual,
Index scanrelid,
Oid indexid,
List *indexqual,
List *indexorderby,
List *indextlist,
ScanDirection indexscandir)
{
IndexOnlyScan *node = makeNode(IndexOnlyScan);
Plan *plan = &node->scan.plan;
plan->targetlist = qptlist;
plan->qual = qpqual;
plan->lefttree = NULL;
plan->righttree = NULL;
node->scan.scanrelid = scanrelid;
node->indexid = indexid;
node->indexqual = indexqual;
node->indexorderby = indexorderby;
node->indextlist = indextlist;
node->indexorderdir = indexscandir;
return node;
}
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-# where dw.dwbh in ('1001','1002')
testdb-# order by dw.dwbh;
QUERY PLAN
-------------------------------------------------------------------------------------------------
Sort (cost=2010.12..2010.17 rows=20 width=47)
Sort Key: dw.dwbh
-> Nested Loop (cost=14.24..2009.69 rows=20 width=47)
-> Hash Join (cost=13.95..2002.56 rows=20 width=32)
Hash Cond: ((gr.dwbh)::text = (dw.dwbh)::text)
-> Seq Scan on t_grxx gr (cost=0.00..1726.00 rows=100000 width=16)
-> Hash (cost=13.92..13.92 rows=2 width=20)
-> Index Scan using t_dwxx_pkey on t_dwxx dw (cost=0.29..13.92 rows=2 width=20)
Index Cond: ((dwbh)::text = ANY ('{1001,1002}'::text[]))
-> Index Scan using idx_t_jfxx_grbh on t_jfxx jf (cost=0.29..0.35 rows=1 width=20)
Index Cond: ((grbh)::text = (gr.grbh)::text)
(11 rows)
启动gdb,设置断点,进入函数create_scan_plan
(gdb) b create_scan_plan
Breakpoint 1 at 0x7b7b78: file createplan.c, line 514.
(gdb) c
Continuing.
Breakpoint 1, create_scan_plan (root=0x2d36d00, best_path=0x2d57ad0, flags=0) at createplan.c:514
514 RelOptInfo *rel = best_path->parent;
pathtype为T_SeqScan
(gdb) p best_path->pathtype
$1 = T_SeqScan
进入相应的分支,约束条件直接使用Relation的限制条件
(gdb) n
532 switch (best_path->pathtype)
(gdb)
539 scan_clauses = rel->baserestrictinfo;
(gdb)
540 break;
非索引快速扫描,构建目标投影列
(gdb) n
559 if (gating_clauses)
(gdb)
572 if (flags == CP_IGNORE_TLIST)
(gdb)
576 else if (use_physical_tlist(root, best_path, flags))
(gdb)
578 if (best_path->pathtype == T_IndexOnlyScan)
(gdb)
592 tlist = build_physical_tlist(root, rel);
(gdb)
593 if (tlist == NIL)
(gdb)
601 if (flags & CP_LABEL_TLIST)
(gdb)
(gdb) p *tlist
$4 = {type = T_List, length = 5, head = 0x2d89440, tail = 0x2d897d8}
(gdb) p *(Node *)tlist->head->data.ptr_value
$5 = {type = T_TargetEntry}
(gdb) p *(TargetEntry *)tlist->head->data.ptr_value
$6 = {xpr = {type = T_TargetEntry}, expr = 0x2d89390, resno = 1, resname = 0x0, ressortgroupref = 0, resorigtbl = 0,
resorigcol = 0, resjunk = false}
根据pathtype进入相应的处理逻辑,调用函数create_seqscan_plan
(gdb) n
614 plan = (Plan *) create_seqscan_plan(root,
(gdb) step
create_seqscan_plan (root=0x2d36d00, best_path=0x2d57ad0, tlist=0x2d89468, scan_clauses=0x0) at createplan.c:2444
2444 Index scan_relid = best_path->parent->relid;
构建扫描条件,为NULL
2451 scan_clauses = order_qual_clauses(root, scan_clauses);
(gdb)
2454 scan_clauses = extract_actual_clauses(scan_clauses, false);
(gdb)
2457 if (best_path->param_info)
(gdb)
(gdb) p *scan_clauses
Cannot access memory at address 0x0
生成SeqScan Plan节点,并把启动成本/总成本等相关信息拷贝到该Plan中
(gdb) n
2463 scan_plan = make_seqscan(tlist,
(gdb)
2467 copy_generic_path_info(&scan_plan->plan, best_path);
完成创建,返回Plan
(gdb) n
2469 return scan_plan;
(gdb) p *scan_plan
$1 = {plan = {type = T_SeqScan, startup_cost = 0, total_cost = 1726, plan_rows = 100000, plan_width = 16,
parallel_aware = false, parallel_safe = true, plan_node_id = 0, targetlist = 0x2db4e38, qual = 0x0, lefttree = 0x0,
righttree = 0x0, initPlan = 0x0, extParam = 0x0, allParam = 0x0}, scanrelid = 3}
下面跟踪分析create_indexscan_plan函数
设置断点,进入函数
(gdb) b create_indexscan_plan
Breakpoint 2 at 0x7badad: file createplan.c, line 2536.
(gdb) c
Continuing.
Breakpoint 1, create_scan_plan (root=0x2d50a00, best_path=0x2da9e98, flags=2) at createplan.c:514
514 RelOptInfo *rel = best_path->parent;
(gdb) c
Continuing.
Breakpoint 2, create_indexscan_plan (root=0x2d50a00, best_path=0x2da9e98, tlist=0x2db5250, scan_clauses=0x2da8998,
indexonly=false) at createplan.c:2536
2536 List *indexquals = best_path->indexquals;
(gdb)
赋值并获取相关信息
2536 List *indexquals = best_path->indexquals;
(gdb) n
2537 List *indexorderbys = best_path->indexorderbys;
(gdb)
2538 Index baserelid = best_path->path.parent->relid;
(gdb)
2539 Oid indexoid = best_path->indexinfo->indexoid;
(gdb)
2544 List *indexorderbyops = NIL;
(gdb)
2548 Assert(baserelid > 0);
(gdb)
2549 Assert(best_path->path.parent->rtekind == RTE_RELATION);
(gdb)
2555 stripped_indexquals = get_actual_clauses(indexquals);
(gdb) n
2561 fixed_indexquals = fix_indexqual_references(root, best_path);
(gdb)
2566 fixed_indexorderbys = fix_indexorderby_references(root, best_path);
(gdb)
2596 qpqual = NIL;
(gdb)
(gdb) p baserelid
$3 = 1
(gdb) p indexoid
$4 = 16738
#t_dwxx_pkey
testdb=# select relname from pg_class where oid=16738;
relname
-------------
t_dwxx_pkey
(1 row)
遍历扫描条件
2597 foreach(l, scan_clauses)
(gdb) p *scan_clauses
$5 = {type = T_List, length = 1, head = 0x2da8970, tail = 0x2da8970}
重复的约束条件,不需要处理
2603 if (list_member_ptr(indexquals, rinfo))
(gdb)
2604 continue;
对条件进行排序&规约
2614 qpqual = order_qual_clauses(root, qpqual);
(gdb) n
2617 qpqual = extract_actual_clauses(qpqual, false);
(gdb) n
2628 if (best_path->path.param_info)
(gdb) p *qpqual
Cannot access memory at address 0x0
创建IndexScan节点
(gdb) n
2642 if (indexorderbys)
(gdb)
2673 if (indexonly)
(gdb)
2683 scan_plan = (Scan *) make_indexscan(tlist,
(gdb)
2694 copy_generic_path_info(&scan_plan->plan, &best_path->path);
(gdb)
2696 return scan_plan;
(gdb)
2697 }
(gdb) p *scan_plan
$6 = {plan = {type = T_IndexScan, startup_cost = 0.28500000000000003, total_cost = 13.924222117799655, plan_rows = 2,
plan_width = 20, parallel_aware = false, parallel_safe = true, plan_node_id = 0, targetlist = 0x2db5250, qual = 0x0,
lefttree = 0x0, righttree = 0x0, initPlan = 0x0, extParam = 0x0, allParam = 0x0}, scanrelid = 1}
(gdb)
回到create_scan_plan
(gdb) n
create_scan_plan (root=0x2d50a00, best_path=0x2da9e98, flags=2) at createplan.c:633
633 break;
(gdb)
732 if (gating_clauses)
(gdb)
735 return plan;
(gdb)
736 }
调用完成.
四、参考资料
createplan.c
PG Document:Query Planning
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