这篇文章主要讲解了“PostgreSQL中ExecProcNode和ExecProcNodeFirst函数的实现逻辑是什么”，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ExecProcNode和ExecProcNodeFirst函数的实现逻辑是什么”吧！
一、基础信息
ExecProcNode/ExecProcNodeFirst函数使用的数据结构、宏定义以及依赖的函数等。
数据结构/宏定义
1、ExecProcNodeMtd
ExecProcNodeMtd是一个函数指针类型，指向的函数输入参数是PlanState结构体指针，输出参数是TupleTableSlot 结构体指针
typedef TupleTableSlot *(*ExecProcNodeMtd) (struct PlanState *pstate);依赖的函数
1、check_stack_depth
//检查stack的深度，如超出系统限制，则主动报错
void
check_stack_depth(void)
{
if (stack_is_too_deep())
{
ereport(ERROR,
(errcode(ERRCODE_STATEMENT_TOO_COMPLEX),
errmsg("stack depth limit exceeded"),
errhint("Increase the configuration parameter \"max_stack_depth\" (currently %dkB), "
"after ensuring the platform's stack depth limit is adequate.",
max_stack_depth)));
}
}
bool
stack_is_too_deep(void)
{
char stack_top_loc;
long stack_depth;
stack_depth = (long) (stack_base_ptr - &stack_top_loc);
if (stack_depth < 0)
stack_depth = -stack_depth;
if (stack_depth > max_stack_depth_bytes &&
stack_base_ptr != NULL)
return true;
#if defined(__ia64__) || defined(__ia64)
stack_depth = (long) (ia64_get_bsp() - register_stack_base_ptr);
if (stack_depth > max_stack_depth_bytes &&
register_stack_base_ptr != NULL)
return true;
#endif
return false;
}2、ExecProcNodeInstr
static TupleTableSlot *
ExecProcNodeInstr(PlanState *node)
{
TupleTableSlot *result;
InstrStartNode(node->instrument);
result = node->ExecProcNodeReal(node);
InstrStopNode(node->instrument, TupIsNull(result) ? 0.0 : 1.0);
return result;
}二、源码解读
1、ExecProcNode
//外部调用者可通过改变node实现遍历
#ifndef FRONTEND
static inline TupleTableSlot *
ExecProcNode(PlanState *node)
{
if (node->chgParam != NULL)
ExecReScan(node);
return node->ExecProcNode(node);
}
#endif2、ExecProcNodeFirst
static TupleTableSlot *
ExecProcNodeFirst(PlanState *node)
{
//检查Stack是否超深
check_stack_depth();
//如果instrument（TODO）
if (node->instrument)
node->ExecProcNode = ExecProcNodeInstr;
else
node->ExecProcNode = node->ExecProcNodeReal;
//执行该Node的处理过程
return node->ExecProcNode(node);
}三、跟踪分析
插入测试数据：
testdb=# -- 获取pid
testdb=# select pg_backend_pid();
pg_backend_pid
----------------
2835
(1 row)
testdb=# -- 插入1行
testdb=# insert into t_insert values(14,'ExecProcNodeFirst','ExecProcNodeFirst','ExecProcNodeFirst');
(挂起)启动gdb分析：
[root@localhost ~]# gdb -p 2835
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-100.el7
Copyright (C) 2013 Free Software Foundation, Inc.
...
(gdb) b ExecProcNodeFirst
Breakpoint 1 at 0x69a797: file execProcnode.c, line 433.
(gdb) c
Continuing.
Breakpoint 1, ExecProcNodeFirst (node=0x2cca790) at execProcnode.c:433
433 check_stack_depth();
#查看输入参数
(gdb) p *node
$1 = {type = T_ModifyTableState, plan = 0x2c1d028, state = 0x2cca440, ExecProcNode = 0x69a78b <ExecProcNodeFirst>, ExecProcNodeReal = 0x6c2485 <ExecModifyTable>, instrument = 0x0,
worker_instrument = 0x0, qual = 0x0, lefttree = 0x0, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, chgParam = 0x0, ps_ResultTupleSlot = 0x2ccb6a0, ps_ExprContext = 0x0, ps_ProjInfo = 0x0,
scandesc = 0x0}
#ExecProcNode 实际对应的函数是ExecProcNodeFirst
#ExecProcNodeReal 实际对应的函数是ExecModifyTable（上一章节已粗略解析）
(gdb) next
440 if (node->instrument)
(gdb)
#实际调用ExecModifyTable函数（这个函数由更高层的调用函数植入）
443 node->ExecProcNode = node->ExecProcNodeReal;
(gdb)
445 return node->ExecProcNode(node);
(gdb) next
#第二次调用（TODO）
Breakpoint 1, ExecProcNodeFirst (node=0x2ccac80) at execProcnode.c:433
433 check_stack_depth();
(gdb) next
440 if (node->instrument)
(gdb) next
443 node->ExecProcNode = node->ExecProcNodeReal;
(gdb) next
445 return node->ExecProcNode(node);
(gdb) next
446 }
(gdb) next
ExecProcNode (node=0x2ccac80) at ../../../src/include/executor/executor.h:238
238 }
#第二次调用的参数
(gdb) p *node
$2 = {type = T_ResultState, plan = 0x2cd0488, state = 0x2cca440, ExecProcNode = 0x6c5094 <ExecResult>, ExecProcNodeReal = 0x6c5094 <ExecResult>, instrument = 0x0, worker_instrument = 0x0, qual = 0x0,
lefttree = 0x0, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, chgParam = 0x0, ps_ResultTupleSlot = 0x2ccad90, ps_ExprContext = 0x2ccab30, ps_ProjInfo = 0x2ccabc0, scandesc = 0x0}
#ExecProcNode对应的实际函数是ExecResult
(gdb)感谢各位的阅读，以上就是“PostgreSQL中ExecProcNode和ExecProcNodeFirst函数的实现逻辑是什么”的内容了，经过本文的学习后，相信大家对PostgreSQL中ExecProcNode和ExecProcNodeFirst函数的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！
