Remove useless lookup of root partitioned rel in ExecInitModifyTable().

node->partitioned_rels is only set in UPDATE/DELETE cases, but
ExecInitModifyTable only uses its "rel" variable in INSERT cases,
so the extra logic to find the root rel is just a waste of complexity
and cycles.

Etsuro Fujita, reviewed by Amit Langote

Discussion: https://postgr.es/m/93cf9816-2f7d-0f67-8ed2-4a4e497a6ab8@lab.ntt.co.jp

src/backend/executor/nodeModifyTable.c

@@ -46,7 +46,6 @@
 #include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/nodeFuncs.h"
-#include "parser/parsetree.h"
 #include "storage/bufmgr.h"
 #include "storage/lmgr.h"
 #include "utils/builtins.h"
@@ -1932,20 +1931,8 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 
 	estate->es_result_relation_info = saved_resultRelInfo;
 
-	/* The root table RT index is at the head of the partitioned_rels list */
-	if (node->partitioned_rels)
-	{
-		Index		root_rti;
-		Oid			root_oid;
-
-		root_rti = linitial_int(node->partitioned_rels);
-		root_oid = getrelid(root_rti, estate->es_range_table);
-		rel = heap_open(root_oid, NoLock);	/* locked by InitPlan */
-	}
-	else
-		rel = mtstate->resultRelInfo->ri_RelationDesc;
-
 	/* Build state for INSERT tuple routing */
+	rel = mtstate->resultRelInfo->ri_RelationDesc;
 	if (operation == CMD_INSERT &&
 		rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 	{
@@ -2118,10 +2105,6 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 		mtstate->ps.ps_ExprContext = NULL;
 	}
 
-	/* Close the root partitioned rel if we opened it above. */
-	if (rel != mtstate->resultRelInfo->ri_RelationDesc)
-		heap_close(rel, NoLock);
-
 	/*
 	 * If needed, Initialize target list, projection and qual for ON CONFLICT
 	 * DO UPDATE.