Throw an error when updating hash columns on utility mode. (#5978)

This commit fix Github Issue 5976.
Co-authored-by: NZhenghua Lyu <zlv@pivotal.io>
Co-authored-by: NShujie Zhang <shzhang@pivotal.io>

src/backend/optimizer/plan/createplan.c

@@ -6776,6 +6776,13 @@ adjust_modifytable_flow(PlannerInfo *root, ModifyTable *node)
 					List	   *hashExpr;
 					Plan	*new_subplan;
 
+					if (Gp_role == GP_ROLE_UTILITY)
+					{
+						ereport(ERROR,
+								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+								 errmsg("Cannot update distribution key columns in utility mode")));
+					}
+
 					new_subplan = (Plan *) make_splitupdate(root, (ModifyTable *) node, subplan, rte, rti);
 					hashExpr = getExprListFromTargetList(new_subplan->targetlist,
 														 targetPolicy->nattrs,

src/test/isolation2/expected/update_hash_col_utilitymode.out

+create table t_update_hash_col_utilitymode(c int) distributed by (c);
+CREATE
+
+1U: update t_update_hash_col_utilitymode set c = c + 1;
+ERROR:  Cannot update distribution key columns in utility mode
+
+drop table t_update_hash_col_utilitymode;
+DROP

src/test/isolation2/isolation2_schedule

+# test update hash col under utility mode
+test: update_hash_col_utilitymode
+
 # Tests on global deadlock detector
 test: select_for_update
 test: gdd/prepare

src/test/isolation2/sql/update_hash_col_utilitymode.sql

+create table t_update_hash_col_utilitymode(c int) distributed by (c);
+
+1U: update t_update_hash_col_utilitymode set c = c + 1;
+
+drop table t_update_hash_col_utilitymode;