这篇文章主要介绍“PostgreSQL中ExecutePlan函数与ExecSeqScan函数的作用是什么”，在日常操作中，相信很多人在PostgreSQL中ExecutePlan函数与ExecSeqScan函数的作用是什么问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”PostgreSQL中ExecutePlan函数与ExecSeqScan函数的作用是什么”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
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 void
ExecutePlan(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 FRONTEND
static 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 FRONTEND
static 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 FRONTEND
static inline bool
ExecQual(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) grjf testdb-# 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 ExecutePlan Breakpoint 1 at 0x6db79d: file execMain.c, line 1694. (gdb) c Continuing. 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:1694 warning: 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", ' ' <repeats 24 times>, "from t_grxx gr inner join t_jfxx jf /n", ' ' <repeats 34 times>...,
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 <ExecProcNodeFirst>,
ExecProcNodeReal = 0x716144 <ExecSort>, 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 <printtup>, rStartup = 0x48c5c1 <printtup_startup>, rShutdown = 0x48d02e <printtup_shutdown>,
rDestroy = 0x48d0a7 <printtup_destroy>, mydest = DestRemote}
赋值,准备执行ExecProcNode(ExecSort)
(gdb) n 1699 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) n 1748 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) n 1779 current_tuple_count++; (gdb) p current_tuple_count $10 = 0 (gdb) n 1780 if (numberTuples && numberTuples == current_tuple_count) (gdb) p numberTuples $11 = 0 (gdb) n 1790 }
继续循环,直接满足条件(全部扫描完毕)未知
(gdb) n 1718 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) c Continuing. Breakpoint 2, ExecSeqScan (pstate=0x14e99a0) at nodeSeqscan.c:127 warning: 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 <ExecSeqScan>,
ExecProcNodeReal = 0x714d59 <ExecSeqScan>, 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) n 129 return ExecScan(&node->ss, (gdb) step ExecScan (node=0x14e99a0, accessMtd=0x714c6d <SeqNext>, recheckMtd=0x714d3d <SeqRecheck>) at execScan.c:132 warning: Source file is more recent than executable. 132 qual = node->ps.qual;
ExecScan->投影信息,为NULL
(gdb) p *projInfo Cannot access memory at address 0x0
ExecScan->约束条件为NULL
(gdb) p *qual Cannot 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) n 142 if (!qual && !projInfo) (gdb) 144 ResetExprContext(econtext); (gdb) n 145 return ExecScanFetch(node, accessMtd, recheckMtd);
ExecScan->进入ExecScanFetch
(gdb) step ExecScanFetch (node=0x14e99a0, accessMtd=0x714c6d <SeqNext>, recheckMtd=0x714d3d <SeqRecheck>) at execScan.c:39 39 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) n 41 CHECK_FOR_INTERRUPTS(); (gdb) 43 if (estate->es_epqTuple != NULL) (gdb) p *estate->es_epqTuple Cannot access memory at address 0x0
ExecScan->调用访问方法SeqNext,返回slot
(gdb) n 95 return (*accessMtd) (node); (gdb) n 96 }
ExecScan->回到ExecScan&ExecSeqScan,结束调用
(gdb) n ExecScan (node=0x14e99a0, accessMtd=0x714c6d <SeqNext>, recheckMtd=0x714d3d <SeqRecheck>) at execScan.c:219 219 } (gdb) ExecSeqScan (pstate=0x14e99a0) at nodeSeqscan.c:132 132 } (gdb)
到此，关于“PostgreSQL中ExecutePlan函数与ExecSeqScan函数的作用是什么”的学习就结束了，希望能够解决大家的疑惑。理论与实践的搭配能更好的帮助大家学习，快去试试吧！若想继续学习更多相关知识，请继续关注亿速云网站，小编会继续努力为大家带来更多实用的文章！
原创文章，作者：carmelaweatherly，如若转载，请注明出处：https://blog.ytso.com/205028.html