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pidtestdb=# 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 2835GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-100.el7Copyright (C) 2013 Free Software Foundation, Inc....(gdb) b ExecProcNodeFirstBreakpoint 1 at 0x69a797: file execProcnode.c, line 433.(gdb) cContinuing.Breakpoint 1, ExecProcNodeFirst (node=0x2cca790) at execProcnode.c:433433     check_stack_depth();#查看输入参数(gdb) p *node$1 = {type = T_ModifyTableState, plan = 0x2c1d028, state = 0x2cca440, ExecProcNode = 0x69a78b , ExecProcNodeReal = 0x6c2485 , 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) next440     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:433433     check_stack_depth();(gdb) next440     if (node->instrument)(gdb) next443         node->ExecProcNode = node->ExecProcNodeReal;(gdb) next445     return node->ExecProcNode(node);(gdb) next446 }(gdb) nextExecProcNode (node=0x2ccac80) at ../../../src/include/executor/executor.h:238238 }#第二次调用的参数(gdb) p *node$2 = {type = T_ResultState, plan = 0x2cd0488, state = 0x2cca440, ExecProcNode = 0x6c5094 , ExecProcNodeReal = 0x6c5094 , 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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