PostgreSQL中​ExecutePlan函数与ExecSeqScan函数的作用是什么

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ExecutePlan函数处理查询计划，直到检索到指定数量(参数numbertuple)的元组，并沿着指定的方向扫描。ExecSeqScan函数顺序扫描relation,返回下一个符合条件的元组。

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 *)

/* ---------------- *      Plan node * * All plan nodes "derive" from the Plan structure by having the * Plan structure as the first field.  This ensures that everything works * when nodes are cast to Plan's.  (node pointers are frequently cast to Plan* * when passed around generically in the executor) * 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 *) * * We never actually instantiate any Plan nodes; this is just the common * abstract superclass for all Plan-type nodes. * 从未实例化任何Plan节点;这只是所有Plan-type节点的通用抽象超类。 * ---------------- */typedef struct Plan{    NodeTag     type;//节点类型    /*     * 成本估算信息;estimated execution costs for plan (see costsize.c for more info)     */    Cost        startup_cost;   /* 启动成本;cost expended before fetching any tuples */    Cost        total_cost;     /* 总成本;total cost (assuming all tuples fetched) */    /*     * 优化器估算信息;planner's estimate of result size of this plan step     */    double      plan_rows;      /* 行数;number of rows plan is expected to emit */    int         plan_width;     /* 平均行大小(Byte为单位);average row width in bytes */    /*     * 并行执行相关的信息;information needed for parallel query     */    bool        parallel_aware; /* 是否参与并行执行逻辑?engage parallel-aware logic? */    bool        parallel_safe;  /* 是否并行安全;OK to use as part of parallel plan? */    /*     * Plan类型节点通用的信息.Common structural data for all Plan types.     */    int         plan_node_id;   /* unique across entire final plan tree */    List       *targetlist;     /* target list to be computed at this node */    List       *qual;           /* implicitly-ANDed qual conditions */    struct Plan *lefttree;      /* input plan tree(s) */    struct Plan *righttree;    List       *initPlan;       /* Init Plan nodes (un-correlated expr                                 * subselects) */    /*     * Information for management of parameter-change-driven rescanning     * parameter-change-driven重扫描的管理信息.     *      * extParam includes the paramIDs of all external PARAM_EXEC params     * affecting this plan node or its children.  setParam params from the     * node's initPlans are not included, but their extParams are.     *     * allParam includes all the extParam paramIDs, plus the IDs of local     * params that affect the node (i.e., the setParams of its initplans).     * These are _all_ the PARAM_EXEC params that affect this node.     */    Bitmapset  *extParam;    Bitmapset  *allParam;} Plan;

二、源码解读

ExecutePlan
PortalRunSelect->ExecutorRun->ExecutePlan函数处理查询计划，直到检索到指定数量(参数numbertuple)的元组，并沿着指定的方向扫描.

/* ---------------------------------------------------------------- *      ExecutePlan * *      Processes the query plan until we have retrieved 'numberTuples' tuples, *      moving in the specified direction. *      处理查询计划，直到检索到指定数量(参数numbertuple)的元组，并沿着指定的方向移动。 * *      Runs to completion if numberTuples is 0 *      如参数numbertuple为0,则运行至结束为止 * * Note: the ctid attribute is a 'junk' attribute that is removed before the * user can see it * 注意:ctid属性是"junk"属性,在返回给用户前会移除 * ---------------------------------------------------------------- */static voidExecutePlan(EState *estate,//执行状态            PlanState *planstate,//计划状态            bool use_parallel_mode,//是否使用并行模式            CmdType operation,//操作类型            bool sendTuples,//是否需要传输元组            uint64 numberTuples,//元组数量            ScanDirection direction,//扫描方向            DestReceiver *dest,//接收的目标端            bool execute_once)//是否只执行一次{    TupleTableSlot *slot;//元组表Slot    uint64      current_tuple_count;//当前的元组计数    /*     * initialize local variables     * 初始化本地变量     */    current_tuple_count = 0;    /*     * Set the direction.     * 设置扫描方向     */    estate->es_direction = direction;    /*     * If the plan might potentially be executed multiple times, we must force     * it to run without parallelism, because we might exit early.     * 如果计划可能被多次执行，那么必须强制它在非并行的情况下运行，因为可能会提前退出。     */    if (!execute_once)        use_parallel_mode = false;//如需多次执行,则不允许并行执行    estate->es_use_parallel_mode = use_parallel_mode;    if (use_parallel_mode)        EnterParallelMode();//如并行,则进入并行模式    /*     * Loop until we've processed the proper number of tuples from the plan.     * 循环直至执行计划已处理完成相应数量的元组     * 注意:每次循环只处理一个元组,每次都要重置元组Expr的上下文/过滤不需要的列/发送元组     */    for (;;)    {        /* Reset the per-output-tuple exprcontext */        //重置Expr上下文        ResetPerTupleExprContext(estate);        /*         * Execute the plan and obtain a tuple         * 执行计划,获取一个元组         */        slot = ExecProcNode(planstate);        /*         * if the tuple is null, then we assume there is nothing more to         * process so we just end the loop...         * 如果返回的元组为空，那么可以认为没有什么要处理的了，结束循环……         */        if (TupIsNull(slot))        {            /*             * If we know we won't need to back up, we can release resources             * at this point.             * 如果已知不需要备份(回溯),那么可以释放资源了             */            if (!(estate->es_top_eflags & EXEC_FLAG_BACKWARD))                (void) ExecShutdownNode(planstate);            break;        }        /*         * If we have a junk filter, then project a new tuple with the junk         * removed.         * 如有junk过滤器,使用junk执行投影操作,产生一个新的元组         *          * Store this new "clean" tuple in the junkfilter's resultSlot.         * (Formerly, we stored it back over the "dirty" tuple, which is WRONG         * because that tuple slot has the wrong descriptor.)         * 将这个新的"clean"元组存储在junkfilter的resultSlot中。         * (以前，将其存储在"dirty" tuple上，这是错误的，因为该tuple slot的描述符是错误的。)         */        if (estate->es_junkFilter != NULL)            slot = ExecFilterJunk(estate->es_junkFilter, slot);        /*         * If we are supposed to send the tuple somewhere, do so. (In         * practice, this is probably always the case at this point.)         * 如果要将元组发送到某个地方(接收器)，那么就这样做。         * (实际上，在这一点上可能总是如此。)         */        if (sendTuples)        {            /*             * If we are not able to send the tuple, we assume the destination             * has closed and no more tuples can be sent. If that's the case,             * end the loop.             * 如果不能发送元组，有理由假设目的接收器已经关闭，不能发送更多元组，结束循环。             */            if (!dest->receiveSlot(slot, dest))                break;//跳出循环        }        /*         * Count tuples processed, if this is a SELECT.  (For other operation         * types, the ModifyTable plan node must count the appropriate         * events.)         * 如果操作类型为CMD_SELECT，则计算已处理的元组。         * (对于其他操作类型，ModifyTable plan节点必须统计合适的事件。)         */        if (operation == CMD_SELECT)            (estate->es_processed)++;        /*         * check our tuple count.. if we've processed the proper number then         * quit, else loop again and process more tuples.  Zero numberTuples         * means no limit.         * 检查处理的元组计数…         * 如果已完成处理，那么退出，否则再次循环并处理更多元组。         * 注意:numberTuples=0表示没有限制。         */        current_tuple_count++;        if (numberTuples && numberTuples == current_tuple_count)        {            /*             * If we know we won't need to back up, we can release resources             * at this point.             * 不需要回溯，可以在此时释放资源。             */            if (!(estate->es_top_eflags & EXEC_FLAG_BACKWARD))                (void) ExecShutdownNode(planstate);            break;        }    }    if (use_parallel_mode)        ExitParallelMode();//退出并行模式}/* ---------------------------------------------------------------- *      ExecProcNode * *      Execute the given node to return a(nother) tuple. *      调用node->ExecProcNode函数返回元组(one or another) * ---------------------------------------------------------------- */#ifndef FRONTENDstatic inline TupleTableSlot *ExecProcNode(PlanState *node){    if (node->chgParam != NULL) /* 参数变化?something changed? */        ExecReScan(node);       /* 调用ExecReScan函数;let ReScan handle this */    return node->ExecProcNode(node);//执行ExecProcNode}#endif

ExecSeqScan
ExecSeqScan函数顺序扫描relation,返回下一个符合条件的元组。

/* ---------------------------------------------------------------- *      ExecSeqScan(node) *       *      Scans the relation sequentially and returns the next qualifying *      tuple. *      We call the ExecScan() routine and pass it the appropriate *      access method functions. *      顺序扫描relation,返回下一个符合条件的元组。 *      调用ExecScan函数,传入相应的访问方法函数 * ---------------------------------------------------------------- */static TupleTableSlot *ExecSeqScan(PlanState *pstate){    SeqScanState *node = castNode(SeqScanState, pstate);//获取SeqScanState    return ExecScan(&node->ss,                    (ExecScanAccessMtd) SeqNext,                    (ExecScanRecheckMtd) SeqRecheck);//执行Scan}/* ---------------------------------------------------------------- *      ExecScan * *      Scans the relation using the 'access method' indicated and *      returns the next qualifying tuple in the direction specified *      in the global variable ExecDirection. *      The access method returns the next tuple and ExecScan() is *      responsible for checking the tuple returned against the qual-clause. *      使用指定的"访问方法"扫描关系，并按照全局变量ExecDirection中指定的方向返回下一个符合条件的元组。 *      访问方法返回下一个元组，ExecScan()负责根据qual-clause条件子句检查返回的元组是否符合条件。 * *      A 'recheck method' must also be provided that can check an *      arbitrary tuple of the relation against any qual conditions *      that are implemented internal to the access method. *      调用者还必须提供"recheck method"，根据访问方法内部实现的条件检查关系的所有元组。 * *      Conditions: *        -- the "cursor" maintained by the AMI is positioned at the tuple *           returned previously. *      前提条件: *        由AMI负责维护的游标已由先前的处理过程定位. * *      Initial States: *        -- the relation indicated is opened for scanning so that the *           "cursor" is positioned before the first qualifying tuple. *      初始状态: *        在游标可定位返回第一个符合条件的元组前,relation已打开可进行扫描 * ---------------------------------------------------------------- */TupleTableSlot *ExecScan(ScanState *node,         ExecScanAccessMtd accessMtd,   /* 返回元组的访问方法;function returning a tuple */         ExecScanRecheckMtd recheckMtd) //recheck方法{    ExprContext *econtext;//表达式上下文    ExprState  *qual;//表达式状态    ProjectionInfo *projInfo;//投影信息    /*     * Fetch data from node     * 从node中提取数据     */    qual = node->ps.qual;    projInfo = node->ps.ps_ProjInfo;    econtext = node->ps.ps_ExprContext;    /* interrupt checks are in ExecScanFetch */    //在ExecScanFetch中有中断检查    /*     * If we have neither a qual to check nor a projection to do, just skip     * all the overhead and return the raw scan tuple.     * 如果既没有要检查的条件qual,也没有要做的投影操作，那么就跳过所有的操作并返回raw scan元组。     */    if (!qual && !projInfo)    {        ResetExprContext(econtext);        return ExecScanFetch(node, accessMtd, recheckMtd);    }    /*     * Reset per-tuple memory context to free any expression evaluation     * storage allocated in the previous tuple cycle.     * 重置每个元组内存上下文，以释放用于在前一个元组循环中分配的表达式求值内存空间。     */    ResetExprContext(econtext);    /*     * get a tuple from the access method.  Loop until we obtain a tuple that     * passes the qualification.     * 从访问方法中获取一个元组。循环，直到获得通过限定条件的元组。     */    for (;;)    {        TupleTableSlot *slot;//slot变量        slot = ExecScanFetch(node, accessMtd, recheckMtd);//获取slot        /*         * if the slot returned by the accessMtd contains NULL, then it means         * there is nothing more to scan so we just return an empty slot,         * being careful to use the projection result slot so it has correct         * tupleDesc.         * 如果accessMtd方法返回的slot中包含NULL，那么这意味着不再需要扫描了，         * 这时候只需要返回一个空slot，小心使用投影结果slot，这样可以有正确的tupleDesc了。         */        if (TupIsNull(slot))        {            if (projInfo)                return ExecClearTuple(projInfo->pi_state.resultslot);            else                return slot;        }        /*         * place the current tuple into the expr context         * 把当前tuple放入到expr上下文中         */        econtext->ecxt_scantuple = slot;        /*         * check that the current tuple satisfies the qual-clause         * 检查当前的tuple是否符合qual-clause条件         *          * check for non-null qual here to avoid a function call to ExecQual()         * when the qual is null ... saves only a few cycles, but they add up         * ...         * 在这里检查qual是否非空，以避免在qual为空时调用ExecQual()函数…         * 只节省了几个调用周期，但它们加起来……的成本还是蛮可观的         */        if (qual == NULL || ExecQual(qual, econtext))        {            /*             * Found a satisfactory scan tuple.             * 发现一个满足条件的元组             */            if (projInfo)            {                /*                 * Form a projection tuple, store it in the result tuple slot                 * and return it.                 * 构造一个投影元组,存储在结果元组slot中并返回                 */                return ExecProject(projInfo);//执行投影操作并返回            }            else            {                /*                 * Here, we aren't projecting, so just return scan tuple.                 * 不需要执行投影操作,返回元组                 */                return slot;//直接返回            }        }        else            InstrCountFiltered1(node, 1);//instrument计数        /*         * Tuple fails qual, so free per-tuple memory and try again.         * 元组不满足条件,释放资源,重试         */        ResetExprContext(econtext);    }}/* * ExecScanFetch -- check interrupts & fetch next potential tuple * ExecScanFetch -- 检查中断&提前下一个备选元组 * * This routine is concerned with substituting a test tuple if we are * inside an EvalPlanQual recheck.  If we aren't, just execute * the access method's next-tuple routine. * 这个例程是处理测试元组的替换(如果在EvalPlanQual重新检查中)。 * 如果不是在EvalPlanQual中，则执行access方法的next-tuple例程。 */static inline TupleTableSlot *ExecScanFetch(ScanState *node,              ExecScanAccessMtd accessMtd,              ExecScanRecheckMtd recheckMtd){    EState     *estate = node->ps.state;    CHECK_FOR_INTERRUPTS();//检查中断    if (estate->es_epqTuple != NULL)//如es_epqTuple不为NULL()    {        //es_epqTuple字段用于在READ COMMITTED模式中替换更新后的元组后,重新评估是否满足执行计划的条件quals        /*         * We are inside an EvalPlanQual recheck.  Return the test tuple if         * one is available, after rechecking any access-method-specific         * conditions.         * 我们正在EvalPlanQual复查。         * 如果test tuple可用，则在重新检查所有特定于访问方法的条件后返回该元组。         */        Index       scanrelid = ((Scan *) node->ps.plan)->scanrelid;//访问的relid        if (scanrelid == 0)//relid==0        {            TupleTableSlot *slot = node->ss_ScanTupleSlot;            /*             * This is a ForeignScan or CustomScan which has pushed down a             * join to the remote side.  The recheck method is responsible not             * only for rechecking the scan/join quals but also for storing             * the correct tuple in the slot.             * 这是一个ForeignScan或CustomScan，它将下推到远程端。             * recheck方法不仅负责重新检查扫描/连接quals，还负责在slot中存储正确的元组。             */            if (!(*recheckMtd) (node, slot))                ExecClearTuple(slot);   /* 验证不通过,释放资源,不返回元组;would not be returned by scan */            return slot;        }        else if (estate->es_epqTupleSet[scanrelid - 1])//从estate->es_epqTupleSet数组中获取标志        {            TupleTableSlot *slot = node->ss_ScanTupleSlot;//获取slot            /* Return empty slot if we already returned a tuple */            //如已返回元组,则清空slot            if (estate->es_epqScanDone[scanrelid - 1])                return ExecClearTuple(slot);            /* Else mark to remember that we shouldn't return more */            //否则,标记没有返回            estate->es_epqScanDone[scanrelid - 1] = true;            /* Return empty slot if we haven't got a test tuple */            //如test tuple为NULL,则清空slot            if (estate->es_epqTuple[scanrelid - 1] == NULL)                return ExecClearTuple(slot);            /* Store test tuple in the plan node's scan slot */            //在计划节点的scan slot中存储test tuple            ExecStoreHeapTuple(estate->es_epqTuple[scanrelid - 1],                               slot, false);            /* Check if it meets the access-method conditions */            //检查是否满足访问方法条件            if (!(*recheckMtd) (node, slot))                ExecClearTuple(slot);   /* 不满足,清空slot;would not be returned by scan */            return slot;        }    }    /*     * Run the node-type-specific access method function to get the next tuple     * 运行node-type-specific方法函数,获取下一个tuple     */    return (*accessMtd) (node);}/* * ExecProject * * Projects a tuple based on projection info and stores it in the slot passed * to ExecBuildProjectInfo(). * 根据投影信息投影一个元组，并将其存储在传递给ExecBuildProjectInfo()的slot中。 * * Note: the result is always a virtual tuple; therefore it may reference * the contents of the exprContext's scan tuples and/or temporary results * constructed in the exprContext.  If the caller wishes the result to be * valid longer than that data will be valid, he must call ExecMaterializeSlot * on the result slot. * 注意:结果总是一个虚拟元组; * 因此，它可以引用exprContext的扫描元组和/或exprContext中构造的临时结果的内容。 * 如果调用者希望结果有效的时间长于数据有效的时间，必须在结果slot上调用ExecMaterializeSlot。 */#ifndef FRONTENDstatic inline TupleTableSlot *ExecProject(ProjectionInfo *projInfo){    ExprContext *econtext = projInfo->pi_exprContext;    ExprState  *state = &projInfo->pi_state;    TupleTableSlot *slot = state->resultslot;    bool        isnull;    /*     * Clear any former contents of the result slot.  This makes it safe for     * us to use the slot's Datum/isnull arrays as workspace.     * 清除以前的结果slot内容。     * 这使得我们可以安全地使用slot的Datum/isnull数组作为工作区。     */    ExecClearTuple(slot);    /* Run the expression, discarding scalar result from the last column. */    //运行表达式，从最后一列丢弃scalar结果。    (void) ExecEvalExprSwitchContext(state, econtext, &isnull);    /*     * Successfully formed a result row.  Mark the result slot as containing a     * valid virtual tuple (inlined version of ExecStoreVirtualTuple()).     * 成功形成了一个结果行。     * 将结果slot标记为包含一个有效的虚拟元组(ExecStoreVirtualTuple()的内联版本)。     */    slot->tts_flags &= ~TTS_FLAG_EMPTY;    slot->tts_nvalid = slot->tts_tupleDescriptor->natts;    return slot;}#endif/* * ExecQual - evaluate a qual prepared with ExecInitQual (possibly via * ExecPrepareQual).  Returns true if qual is satisfied, else false. * 解析用ExecInitQual准备的条件qual(可能通过ExecPrepareQual)。 * 如果满足条件qual，返回true，否则为false。 *  * Note: ExecQual used to have a third argument "resultForNull".  The * behavior of this function now corresponds to resultForNull == false. * If you want the resultForNull == true behavior, see ExecCheck. * 注意:ExecQual曾经有第三个参数"resultForNull"。 * 这个函数的行为现在对应于resultForNull == false。 * 如果希望resultForNull == true行为，请参阅ExecCheck。 */#ifndef FRONTENDstatic inline boolExecQual(ExprState *state, ExprContext *econtext){    Datum       ret;    bool        isnull;    /* short-circuit (here and in ExecInitQual) for empty restriction list */    //如state为NULL,直接返回    if (state == NULL)        return true;    /* verify that expression was compiled using ExecInitQual */    //使用函数ExecInitQual验证表达式是否可以编译    Assert(state->flags & EEO_FLAG_IS_QUAL);    ret = ExecEvalExprSwitchContext(state, econtext, &isnull);    /* EEOP_QUAL不应返回NULL;EEOP_QUAL should never return NULL */    Assert(!isnull);    return DatumGetBool(ret);}#endif/* -------------------------------- *      ExecClearTuple * *      This function is used to clear out a slot in the tuple table. *      该函数清空tuple table中的slot *      NB: only the tuple is cleared, not the tuple descriptor (if any). *      注意:只有tuple被清除,而不是tuple描述符 * -------------------------------- */TupleTableSlot *                /* 返回验证通过的slot;return: slot passed */ExecClearTuple(TupleTableSlot *slot)    /* 存储tuple的slot;slot in which to store tuple */{    /*     * sanity checks     * 安全检查     */    Assert(slot != NULL);    /*     * Free the old physical tuple if necessary.     * 如需要,释放原有的物理元组     */    if (TTS_SHOULDFREE(slot))    {        heap_freetuple(slot->tts_tuple);//释放元组        slot->tts_flags &= ~TTS_FLAG_SHOULDFREE;    }    if (TTS_SHOULDFREEMIN(slot))    {        heap_free_minimal_tuple(slot->tts_mintuple);        slot->tts_flags &= ~TTS_FLAG_SHOULDFREEMIN;    }    slot->tts_tuple = NULL;//设置NULL值    slot->tts_mintuple = NULL;    /*     * Drop the pin on the referenced buffer, if there is one.     * 如果有的话，将pin放在已引用的缓冲区上。     */    if (BufferIsValid(slot->tts_buffer))        ReleaseBuffer(slot->tts_buffer);//释放缓冲区    slot->tts_buffer = InvalidBuffer;    /*     * Mark it empty.     * 标记为空     */    slot->tts_flags |= TTS_FLAG_EMPTY;    slot->tts_nvalid = 0;    return slot;}

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) grjftestdb-# 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ExecutePlan

(gdb) b ExecutePlanBreakpoint 1 at 0x6db79d: file execMain.c, line 1694.(gdb) cContinuing.Breakpoint 1, ExecutePlan (estate=0x14daf48, planstate=0x14db160, use_parallel_mode=false, operation=CMD_SELECT,     sendTuples=true, numberTuples=0, direction=ForwardScanDirection, dest=0x14d9ed0, execute_once=true) at execMain.c:1694warning: Source file is more recent than executable.1694        current_tuple_count = 0;

查看输入参数
planstate->type:T_SortState->排序Plan
planstate->ExecProcNode:ExecProcNodeFirst,封装器
planstate->ExecProcNodeReal:ExecSort,实际的函数
use_parallel_mode:false,非并行模式
operation:CMD_SELECT,查询操作
sendTuples:T,需要发送元组给客户端
numberTuples:0,所有元组
direction:ForwardScanDirection
dest:printtup(console客户端)
execute_once:T,只执行一次

(gdb) p *estate$1 = {type = T_EState, es_direction = ForwardScanDirection, es_snapshot = 0x1493e10, es_crosscheck_snapshot = 0x0,   es_range_table = 0x14d7c00, es_plannedstmt = 0x14d9d58,   es_sourceText = 0x13eeeb8 "select dw.*,grjf.grbh,grjf.xm,grjf.ny,grjf.je \nfrom t_dwxx dw,lateral (select gr.grbh,gr.xm,jf.ny,jf.je \n", ' ' , "from t_grxx gr inner join t_jfxx jf \n", ' ' ...,   es_junkFilter = 0x0, es_output_cid = 0, es_result_relations = 0x0, es_num_result_relations = 0,   es_result_relation_info = 0x0, es_root_result_relations = 0x0, es_num_root_result_relations = 0,   es_tuple_routing_result_relations = 0x0, es_trig_target_relations = 0x0, es_trig_tuple_slot = 0x0,   es_trig_oldtup_slot = 0x0, es_trig_newtup_slot = 0x0, es_param_list_info = 0x0, es_param_exec_vals = 0x0,   es_queryEnv = 0x0, es_query_cxt = 0x14dae30, es_tupleTable = 0x14dbaf8, es_rowMarks = 0x0, es_processed = 0,   es_lastoid = 0, es_top_eflags = 16, es_instrument = 0, es_finished = false, es_exprcontexts = 0x14db550,   es_subplanstates = 0x0, es_auxmodifytables = 0x0, es_per_tuple_exprcontext = 0x0, es_epqTuple = 0x0,   es_epqTupleSet = 0x0, es_epqScanDone = 0x0, es_use_parallel_mode = false, es_query_dsa = 0x0, es_jit_flags = 0,   es_jit = 0x0, es_jit_worker_instr = 0x0}(gdb) p *planstate$2 = {type = T_SortState, plan = 0x14d3f90, state = 0x14daf48, ExecProcNode = 0x6e41bb ,   ExecProcNodeReal = 0x716144 , instrument = 0x0, worker_instrument = 0x0, worker_jit_instrument = 0x0,   qual = 0x0, lefttree = 0x14db278, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, chgParam = 0x0,   ps_ResultTupleSlot = 0x14ec470, ps_ExprContext = 0x0, ps_ProjInfo = 0x0, scandesc = 0x14e9fd0}(gdb) p *dest$4 = {receiveSlot = 0x48cc00 , rStartup = 0x48c5c1 , rShutdown = 0x48d02e ,   rDestroy = 0x48d0a7 , mydest = DestRemote}

赋值,准备执行ExecProcNode(ExecSort)

(gdb) n1699        estate->es_direction = direction;(gdb) 1705        if (!execute_once)(gdb) 1708        estate->es_use_parallel_mode = use_parallel_mode;(gdb) 1709        if (use_parallel_mode)(gdb) 1718            ResetPerTupleExprContext(estate);(gdb) 1723            slot = ExecProcNode(planstate);(gdb)

执行ExecProcNode(ExecSort),返回slot

(gdb) 1729            if (TupIsNull(slot))(gdb) p *slot$5 = {type = T_TupleTableSlot, tts_isempty = false, tts_shouldFree = false, tts_shouldFreeMin = false, tts_slow = false,   tts_tuple = 0x14ec4b0, tts_tupleDescriptor = 0x14ec058, tts_mcxt = 0x14dae30, tts_buffer = 0, tts_nvalid = 0,   tts_values = 0x14ec4d0, tts_isnull = 0x14ec508, tts_mintuple = 0x1a4b078, tts_minhdr = {t_len = 64, t_self = {ip_blkid = {        bi_hi = 0, bi_lo = 0}, ip_posid = 0}, t_tableOid = 0, t_data = 0x1a4b070}, tts_off = 0,   tts_fixedTupleDescriptor = true}

查看slot中的数据
注意:slot中的t_data不是实际的tuple data,而是缓冲区信息,在返回时根据这些信息从缓冲区获取数据返回

(gdb) p *slot$5 = {type = T_TupleTableSlot, tts_isempty = false, tts_shouldFree = false, tts_shouldFreeMin = false, tts_slow = false,   tts_tuple = 0x14ec4b0, tts_tupleDescriptor = 0x14ec058, tts_mcxt = 0x14dae30, tts_buffer = 0, tts_nvalid = 0,   tts_values = 0x14ec4d0, tts_isnull = 0x14ec508, tts_mintuple = 0x1a4b078, tts_minhdr = {t_len = 64, t_self = {ip_blkid = {        bi_hi = 0, bi_lo = 0}, ip_posid = 0}, t_tableOid = 0, t_data = 0x1a4b070}, tts_off = 0,   tts_fixedTupleDescriptor = true}(gdb) p *slot->tts_tuple$6 = {t_len = 64, t_self = {ip_blkid = {bi_hi = 0, bi_lo = 0}, ip_posid = 0}, t_tableOid = 0, t_data = 0x1a4b070}(gdb) p *slot->tts_tuple->t_data$7 = {t_choice = {t_heap = {t_xmin = 21967600, t_xmax = 0, t_field3 = {t_cid = 56, t_xvac = 56}}, t_datum = {      datum_len_ = 21967600, datum_typmod = 0, datum_typeid = 56}}, t_ctid = {ip_blkid = {bi_hi = 0, bi_lo = 0},     ip_posid = 32639}, t_infomask2 = 7, t_infomask = 2, t_hoff = 24 '\030', t_bits = 0x1a4b087 ""}

判断是否需要过滤属性(不需要)

(gdb) n1748            if (estate->es_junkFilter != NULL)(gdb) (gdb) p estate->es_junkFilter$12 = (JunkFilter *) 0x0

修改计数器等信息

(gdb) 1755            if (sendTuples)(gdb) 1762                if (!dest->receiveSlot(slot, dest))(gdb) 1771            if (operation == CMD_SELECT)(gdb) 1772                (estate->es_processed)++;(gdb) p estate->es_processed$9 = 0(gdb) n1779            current_tuple_count++;(gdb) p current_tuple_count$10 = 0(gdb) n1780            if (numberTuples && numberTuples == current_tuple_count)(gdb) p numberTuples$11 = 0(gdb) n1790        }

继续循环,直接满足条件(全部扫描完毕)未知

(gdb) n1718            ResetPerTupleExprContext(estate);(gdb) 1723            slot = ExecProcNode(planstate);(gdb) 1729            if (TupIsNull(slot))...

ExecutePlan的主体逻辑已介绍完毕,下面简单跟踪分析ExecSeqScan函数
设置断点,进入ExecSeqScan

(gdb) del 1(gdb) cContinuing.Breakpoint 2, ExecSeqScan (pstate=0x14e99a0) at nodeSeqscan.c:127warning: Source file is more recent than executable.127     SeqScanState *node = castNode(SeqScanState, pstate);

查看输入参数
plan为SeqScan
ExecProcNode=ExecProcNodeReal,均为函数ExecSeqScan
targetlist为投影列信息

(gdb) p *pstate$13 = {type = T_SeqScanState, plan = 0x14d5570, state = 0x14daf48, ExecProcNode = 0x714d59 ,   ExecProcNodeReal = 0x714d59 , instrument = 0x0, worker_instrument = 0x0, worker_jit_instrument = 0x0,   qual = 0x0, lefttree = 0x0, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, chgParam = 0x0,   ps_ResultTupleSlot = 0x14e9c38, ps_ExprContext = 0x14e9ab8, ps_ProjInfo = 0x0, scandesc = 0x7fa45b442ab8}(gdb) p *pstate->plan$14 = {type = T_SeqScan, startup_cost = 0, total_cost = 164, plan_rows = 10000, plan_width = 20, parallel_aware = false,   parallel_safe = true, plan_node_id = 7, targetlist = 0x14d5438, qual = 0x0, lefttree = 0x0, righttree = 0x0,   initPlan = 0x0, extParam = 0x0, allParam = 0x0}

进入ExecScan函数
accessMtd方法为SeqNext
recheckMtd方法为SeqRecheck

(gdb) n129     return ExecScan(&node->ss,(gdb) stepExecScan (node=0x14e99a0, accessMtd=0x714c6d , recheckMtd=0x714d3d ) at execScan.c:132warning: Source file is more recent than executable.132     qual = node->ps.qual;

ExecScan->投影信息,为NULL

(gdb) p *projInfoCannot access memory at address 0x0

ExecScan->约束条件为NULL

(gdb) p *qualCannot access memory at address 0x0

ExecScan->如果既没有要检查的条件qual,也没有要做的投影操作，那么就跳过所有的操作并返回raw scan元组

(gdb) n142     if (!qual && !projInfo)(gdb) 144         ResetExprContext(econtext);(gdb) n145         return ExecScanFetch(node, accessMtd, recheckMtd);

ExecScan->进入ExecScanFetch

(gdb) stepExecScanFetch (node=0x14e99a0, accessMtd=0x714c6d , recheckMtd=0x714d3d ) at execScan.c:3939      EState     *estate = node->ps.state;

ExecScan->检查中断,判断是否处于EvalPlanQual recheck状态(为NULL,实际不是)

39      EState     *estate = node->ps.state;(gdb) n41      CHECK_FOR_INTERRUPTS();(gdb) 43      if (estate->es_epqTuple != NULL)(gdb) p *estate->es_epqTupleCannot access memory at address 0x0

ExecScan->调用访问方法SeqNext,返回slot

(gdb) n95      return (*accessMtd) (node);(gdb) n96  }

ExecScan->回到ExecScan&ExecSeqScan,结束调用

(gdb) nExecScan (node=0x14e99a0, accessMtd=0x714c6d , recheckMtd=0x714d3d ) at execScan.c:219219 }(gdb) ExecSeqScan (pstate=0x14e99a0) at nodeSeqscan.c:132132 }(gdb)

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