本节介绍ExecModifyTable函数。

相关数据结构

typedef struct ModifyTableState
{
	PlanState	ps;				/* its first field is NodeTag */
	CmdType		operation;		/* INSERT, UPDATE, or DELETE */
	bool		canSetTag;		/* do we set the command tag/es_processed? */
	bool		mt_done;		/* are we done? */
	PlanState **mt_plans;		/* subplans (one per target rel) */
	int			mt_nplans;		/* number of plans in the array */
	int			mt_whichplan;	/* which one is being executed (0..n-1) */
	TupleTableSlot **mt_scans;	/* input tuple corresponding to underlying
								 * plans */
	ResultRelInfo *resultRelInfo;	/* per-subplan target relations */
	ResultRelInfo *rootResultRelInfo;	/* root target relation (partitioned
										 * table root) */
	List	  **mt_arowmarks;	/* per-subplan ExecAuxRowMark lists */
	EPQState	mt_epqstate;	/* for evaluating EvalPlanQual rechecks */
	bool		fireBSTriggers; /* do we need to fire stmt triggers? */
	List	   *mt_excludedtlist;	/* the excluded pseudo relation"s tlist  */

	/*
	 * Slot for storing tuples in the root partitioned table"s rowtype during
	 * an UPDATE of a partitioned table.
	 */
	TupleTableSlot *mt_root_tuple_slot;

	/* Tuple-routing support info */
	struct PartitionTupleRouting *mt_partition_tuple_routing;

	/* controls transition table population for specified operation */
	struct TransitionCaptureState *mt_transition_capture;

	/* controls transition table population for INSERT...ON CONFLICT UPDATE */
	struct TransitionCaptureState *mt_oc_transition_capture;

	/* Per plan map for tuple conversion from child to root */
	TupleConversionMap **mt_per_subplan_tupconv_maps;
} ModifyTableState;

代码100分

ExecModifyTable函数

代码100分static TupleTableSlot *
ExecModifyTable(PlanState *pstate);

/* 检查是否有中断信号 */
CHECK_FOR_INTERRUPTS();

/* ModifyTable不应该在EvalPlanQual操作中执行 */
if (estate->es_epq_active != NULL)
	elog(ERROR, "ModifyTable should not be called during EvalPlanQual");

/* 是否已经完成 */
if (node->mt_done)
	return NULL;

/* 启动BEFORE STATEMENT触发器 */
if (node->fireBSTriggers)
{
	fireBSTriggers(node);
	node->fireBSTriggers = false;
}

/* 先设置一些本地变量 */
resultRelInfo = node->resultRelInfo + node->mt_whichplan;
subplanstate = node->mt_plans[node->mt_whichplan];
junkfilter = resultRelInfo->ri_junkFilter;

/* es_result_relation_info应该指向当前活动的relation */
saved_resultRelInfo = estate->es_result_relation_info;
estate->es_result_relation_info = resultRelInfo;

/* 从子计划中获取rows，并且对每行执行所需的表修改操作 */
for (;;)
{
	/* 重置每个输出元组的expr上下文 */
	ResetPerTupleExprContext(estate);
	
	/* 重置用于处理冲突和返回子句的每行元组的内存上下文，
	 * 以释放在前一个周期中分配的任何表达式求值存储 */
	if (pstate->ps_ExprContext)
		ResetExprContext(pstate->ps_ExprContext);
	
	/* 获取子计划返回的slot */
	planSlot = ExecProcNode(subplanstate);
	
	if (TupIsNull(planSlot))
	{
		/* 前进到下一个子计划（如果有）*/
		node->mt_whichplan++;
		if (node->mt_whichplan < node->mt_nplans)
		{
			resultRelInfo++;
			subplanstate = node->mt_plans[node->mt_whichplan];
			junkfilter = resultRelInfo->ri_junkFilter;
			estate->es_result_relation_info = resultRelInfo;
			/* 设置子计划 */
			EvalPlanQualSetPlan(&node->mt_epqstate, subplanstate->plan,
							node->mt_arowmarks[node->mt_whichplan]);
			/* 获取此子计划的元组转换map */
			if (node->mt_transition_capture != NULL)
			{
				node->mt_transition_capture->tcs_map =
					tupconv_map_for_subplan(node, node->mt_whichplan);
			}
			if (node->mt_oc_transition_capture != NULL)
			{
				node->mt_oc_transition_capture->tcs_map =
					tupconv_map_for_subplan(node, node->mt_whichplan);
			}
			continue;
		}
		else
			break;
	}
	
	/* 若是fdwDirectModify，接下来只需要计算RETURNING表达式就执行完成了 */
	if (resultRelInfo->ri_usesFdwDirectModify)
	{
		Assert(resultRelInfo->ri_projectReturning);

		slot = ExecProcessReturning(resultRelInfo, NULL, planSlot);

		estate->es_result_relation_info = saved_resultRelInfo;
		return slot;
	}
	
	/* 设置子plan的slot */
	EvalPlanQualSetSlot(&node->mt_epqstate, planSlot);
	slot = planSlot;
	
	tupleid = NULL;
	oldtuple = NULL;
	/* 过滤一些属性 */
	if (junkfilter != NULL)
	{
		/* 提取"ctd"或"wholerow"这些“垃圾”属性 */
		if (operation == CMD_UPDATE || operation == CMD_DELETE)
		{
			relkind = resultRelInfo->ri_RelationDesc->rd_rel->relkind;
			if (relkind == RELKIND_RELATION || relkind == RELKIND_MATVIEW)
			{
				datum = ExecGetJunkAttribute(slot,
								 junkfilter->jf_junkAttNo,
								 &isNull);
				/* shouldn"t ever get a null result... */
				if (isNull)
					elog(ERROR, "ctid is NULL");

				tupleid = (ItemPointer) DatumGetPointer(datum);
				tuple_ctid = *tupleid;	/* be sure we don"t free ctid!! */
				tupleid = &tuple_ctid;
			}
			
			/* 使用wholerow属性（如果可用）重建旧的关系元组。*/
			else if (AttributeNumberIsValid(junkfilter->jf_junkAttNo))
			{
				datum = ExecGetJunkAttribute(slot,
								 junkfilter->jf_junkAttNo,
								 &isNull);
				/* shouldn"t ever get a null result... */
				if (isNull)
					elog(ERROR, "wholerow is NULL");

				oldtupdata.t_data = DatumGetHeapTupleHeader(datum);
				oldtupdata.t_len =
					HeapTupleHeaderGetDatumLength(oldtupdata.t_data);
				ItemPointerSetInvalid(&(oldtupdata.t_self));
				/* 历史原因，试图触发器会看到非法的t_tableOid. */
				oldtupdata.t_tableOid =
					(relkind == RELKIND_VIEW) ? InvalidOid :
					RelationGetRelid(resultRelInfo->ri_RelationDesc);

				oldtuple = &oldtupdata;
			}
			else
				Assert(relkind == RELKIND_FOREIGN_TABLE);
		}
		
		/* 有需要时使用“垃圾”过滤器 */
		if (operation != CMD_DELETE)
			slot = ExecFilterJunk(junkfilter, slot);
	}
	
	/* 根据操作类型执行相应操作 */
	switch (operation)
	{
		case CMD_INSERT:
			/* 有需要的话准备元组路由（分区表相关）. */
			if (proute)
				slot = ExecPrepareTupleRouting(node, estate, proute,
									   resultRelInfo, slot);
			slot = ExecInsert(node, slot, planSlot,
						  estate, node->canSetTag);
			/* 还原ExecPrepareTupleRouting的状态更改 */
			if (proute)
				estate->es_result_relation_info = resultRelInfo;
			break;
		case CMD_UPDATE:
			slot = ExecUpdate(node, tupleid, oldtuple, slot, planSlot,
							  &node->mt_epqstate, estate, node->canSetTag);
			break;
		case CMD_DELETE:
			slot = ExecDelete(node, tupleid, oldtuple, planSlot,
							  &node->mt_epqstate, estate,
							  true, node->canSetTag,
							  false /* changingPart */ , NULL, NULL);
			break;
		default:
			elog(ERROR, "unknown operation");
			break;
	}
	
	/* 如果有返回结果，返回给调用者。下此调用本函数时会继续执行 */
	if (slot)
	{
		estate->es_result_relation_info = saved_resultRelInfo;
		return slot;
	}
}

/* 结束函数前恢复es_result_relation_info */
	estate->es_result_relation_info = saved_resultRelInfo;

/* 启动AFTER STATEMENT触发器 */
fireASTriggers(node);

node->mt_done = true;

return NULL;