PostgreSQL中ExecProcNode和ExecProcNodeFirst函数的实现逻辑是什么
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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
/* ---------------- * ExecProcNodeMtd * * This is the method called by ExecProcNode to return the next tuple * from an executor node. It returns NULL, or an empty TupleTableSlot, * if no more tuples are available. * ---------------- */ 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
/*
* check_stack_depth/stack_is_too_deep: check for excessively deep recursion
*
* This should be called someplace in any recursive routine that might possibly
* recurse deep enough to overflow the stack. Most Unixen treat stack
* overflow as an unrecoverable SIGSEGV, so we want to error out ourselves
* before hitting the hardware limit.
*
* check_stack_depth() just throws an error summarily. stack_is_too_deep()
* can be used by code that wants to handle the error condition itself.
*/
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;
/*
* Compute distance from reference point to my local variables
*/
stack_depth = (long) (stack_base_ptr - &stack_top_loc);
/*
* Take abs value, since stacks grow up on some machines, down on others
*/
if (stack_depth < 0)
stack_depth = -stack_depth;
/*
* Trouble?
*
* The test on stack_base_ptr prevents us from erroring out if called
* during process setup or in a non-backend process. Logically it should
* be done first, but putting it here avoids wasting cycles during normal
* cases.
*/
if (stack_depth > max_stack_depth_bytes &&
stack_base_ptr != NULL)
return true;
/*
* On IA64 there is a separate "register" stack that requires its own
* independent check. For this, we have to measure the change in the
* "BSP" pointer from PostgresMain to here. Logic is just as above,
* except that we know IA64's register stack grows up.
*
* Note we assume that the same max_stack_depth applies to both stacks.
*/
#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 /* IA64 */
return false;
}
2、ExecProcNodeInstr
/*
* ExecProcNode wrapper that performs instrumentation calls. By keeping
* this a separate function, we avoid overhead in the normal case where
* no instrumentation is wanted.
*/
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
/* ----------------------------------------------------------------
* ExecProcNode
*
* Execute the given node to return a(nother) tuple.
* ----------------------------------------------------------------
*/
#ifndef FRONTEND
static inline TupleTableSlot *
ExecProcNode(PlanState *node)
{
if (node->chgParam != NULL) /* something changed? */
ExecReScan(node); /* let ReScan handle this */
return node->ExecProcNode(node);
}
#endif
2、ExecProcNodeFirst
/*
* ExecProcNode wrapper that performs some one-time checks, before calling
* the relevant node method (possibly via an instrumentation wrapper).
*/
/*
输入：
node-PlanState指针
输出：
存储Tuple的Slot
*/
static TupleTableSlot *
ExecProcNodeFirst(PlanState *node)
{
/*
* Perform stack depth check during the first execution of the node. We
* only do so the first time round because it turns out to not be cheap on
* some common architectures (eg. x86). This relies on the assumption
* that ExecProcNode calls for a given plan node will always be made at
* roughly the same stack depth.
*/
//检查Stack是否超深
check_stack_depth();
/*
* If instrumentation is required, change the wrapper to one that just
* does instrumentation. Otherwise we can dispense with all wrappers and
* have ExecProcNode() directly call the relevant function from now on.
*/
//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)
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