Clean up code to resolve the "root target relation" in nodeModifyTable.c

When executing DDL on a partitioned table or on a table with inheritance
children, statement-level triggers must be fired against the table given
in the original statement. The code to look that up was a bit messy and
duplicative. Commit 501ed02c added a helper function,
getASTriggerResultRelInfo() (later renamed to getTargetResultRelInfo())
for it, but for some reason it was only used when firing AFTER STATEMENT
triggers and the code to fire BEFORE STATEMENT triggers duplicated the
logic.

Determine the target relation in ExecInitModifyTable(), and set it always
in ModifyTableState. Code that used to call getTargetResultRelInfo() can
now use ModifyTableState->rootResultRelInfo directly.

Discussion: https://www.postgresql.org/message-id/CA%2BHiwqFViT47Zbr_ASBejiK7iDG8%3DQ1swQ-tjM6caRPQ67pT%3Dw%40mail.gmail.com

src/backend/executor/nodeModifyTable.c

@@ -72,7 +72,6 @@ static TupleTableSlot *ExecPrepareTupleRouting(ModifyTableState *mtstate,
 											   ResultRelInfo *targetRelInfo,
 											   TupleTableSlot *slot,
 											   ResultRelInfo **partRelInfo);
-static ResultRelInfo *getTargetResultRelInfo(ModifyTableState *node);
 static void ExecSetupChildParentMapForSubplan(ModifyTableState *mtstate);
 static TupleConversionMap *tupconv_map_for_subplan(ModifyTableState *node,
 												   int whichplan);
@@ -1186,7 +1185,6 @@ ExecCrossPartitionUpdate(ModifyTableState *mtstate,
 		saved_tcs_map = mtstate->mt_transition_capture->tcs_map;
 
 	/* Tuple routing starts from the root table. */
-	Assert(mtstate->rootResultRelInfo != NULL);
 	*inserted_tuple = ExecInsert(mtstate, mtstate->rootResultRelInfo, slot,
 								 planSlot, estate, canSetTag);
 
@@ -1796,15 +1794,7 @@ static void
 fireBSTriggers(ModifyTableState *node)
 {
 	ModifyTable *plan = (ModifyTable *) node->ps.plan;
-	ResultRelInfo *resultRelInfo = node->resultRelInfo;
-
-	/*
-	 * If the node modifies a partitioned table, we must fire its triggers.
-	 * Note that in that case, node->resultRelInfo points to the first leaf
-	 * partition, not the root table.
-	 */
-	if (node->rootResultRelInfo != NULL)
-		resultRelInfo = node->rootResultRelInfo;
+	ResultRelInfo *resultRelInfo = node->rootResultRelInfo;
 
 	switch (node->operation)
 	{
@@ -1826,28 +1816,6 @@ fireBSTriggers(ModifyTableState *node)
 	}
 }
 
-/*
- * Return the target rel ResultRelInfo.
- *
- * This relation is the same as :
- * - the relation for which we will fire AFTER STATEMENT triggers.
- * - the relation into whose tuple format all captured transition tuples must
- *   be converted.
- * - the root partitioned table.
- */
-static ResultRelInfo *
-getTargetResultRelInfo(ModifyTableState *node)
-{
-	/*
-	 * Note that if the node modifies a partitioned table, node->resultRelInfo
-	 * points to the first leaf partition, not the root table.
-	 */
-	if (node->rootResultRelInfo != NULL)
-		return node->rootResultRelInfo;
-	else
-		return node->resultRelInfo;
-}
-
 /*
  * Process AFTER EACH STATEMENT triggers
  */
@@ -1855,7 +1823,7 @@ static void
 fireASTriggers(ModifyTableState *node)
 {
 	ModifyTable *plan = (ModifyTable *) node->ps.plan;
-	ResultRelInfo *resultRelInfo = getTargetResultRelInfo(node);
+	ResultRelInfo *resultRelInfo = node->rootResultRelInfo;
 
 	switch (node->operation)
 	{
@@ -1889,7 +1857,7 @@ static void
 ExecSetupTransitionCaptureState(ModifyTableState *mtstate, EState *estate)
 {
 	ModifyTable *plan = (ModifyTable *) mtstate->ps.plan;
-	ResultRelInfo *targetRelInfo = getTargetResultRelInfo(mtstate);
+	ResultRelInfo *targetRelInfo = mtstate->rootResultRelInfo;
 
 	/* Check for transition tables on the directly targeted relation. */
 	mtstate->mt_transition_capture =
@@ -2019,7 +1987,7 @@ ExecPrepareTupleRouting(ModifyTableState *mtstate,
 static void
 ExecSetupChildParentMapForSubplan(ModifyTableState *mtstate)
 {
-	ResultRelInfo *targetRelInfo = getTargetResultRelInfo(mtstate);
+	ResultRelInfo *targetRelInfo = mtstate->rootResultRelInfo;
 	ResultRelInfo *resultRelInfos = mtstate->resultRelInfo;
 	TupleDesc	outdesc;
 	int			numResultRelInfos = mtstate->mt_nplans;
@@ -2355,13 +2323,31 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 		palloc(nplans * sizeof(ResultRelInfo));
 	mtstate->mt_scans = (TupleTableSlot **) palloc0(sizeof(TupleTableSlot *) * nplans);
 
-	/* If modifying a partitioned table, initialize the root table info */
+	/*----------
+	 * Resolve the target relation. This is the same as:
+	 *
+	 * - the relation for which we will fire FOR STATEMENT triggers,
+	 * - the relation into whose tuple format all captured transition tuples
+	 *   must be converted, and
+	 * - the root partitioned table used for tuple routing.
+	 *
+	 * If it's a partitioned table, the root partition doesn't appear
+	 * elsewhere in the plan and its RT index is given explicitly in
+	 * node->rootRelation.  Otherwise (i.e. table inheritance) the target
+	 * relation is the first relation in the node->resultRelations list, and
+	 * we will initialize it in the loop below.
+	 *----------
+	 */
 	if (node->rootRelation > 0)
 	{
 		mtstate->rootResultRelInfo = makeNode(ResultRelInfo);
 		ExecInitResultRelation(estate, mtstate->rootResultRelInfo,
 							   node->rootRelation);
 	}
+	else
+	{
+		mtstate->rootResultRelInfo = mtstate->resultRelInfo;
+	}
 
 	mtstate->mt_arowmarks = (List **) palloc0(sizeof(List *) * nplans);
 	mtstate->mt_nplans = nplans;
@@ -2446,7 +2432,7 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	}
 
 	/* Get the target relation */
-	rel = (getTargetResultRelInfo(mtstate))->ri_RelationDesc;
+	rel = mtstate->rootResultRelInfo->ri_RelationDesc;
 
 	/*
 	 * If it's not a partitioned table after all, UPDATE tuple routing should

src/include/nodes/execnodes.h

@@ -1154,8 +1154,13 @@ typedef struct ModifyTableState
 	TupleTableSlot **mt_scans;	/* input tuple corresponding to underlying
 								 * plans */
 	ResultRelInfo *resultRelInfo;	/* per-subplan target relations */
-	ResultRelInfo *rootResultRelInfo;	/* root target relation (partitioned
-										 * table root) */
+
+	/*
+	 * Target relation mentioned in the original statement, used to fire
+	 * statement-level triggers and as the root for tuple routing.
+	 */
+	ResultRelInfo *rootResultRelInfo;
+
 	List	  **mt_arowmarks;	/* per-subplan ExecAuxRowMark lists */
 	EPQState	mt_epqstate;	/* for evaluating EvalPlanQual rechecks */
 	bool		fireBSTriggers; /* do we need to fire stmt triggers? */