sessionctx: add testcase for set_var hint (#46784)

ref #45892
pingcap · Sep 8, 2023 · 968c712 · 968c712
1 parent 58a2dad
commit 968c712
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Showing 2 changed files with 26 additions and 1 deletion.
diff --git a/sessionctx/variable/session.go b/sessionctx/variable/session.go
@@ -2536,7 +2536,12 @@ func (s *SessionVars) SetSystemVarWithOldValAsRet(name string, val string) (stri
 	if err != nil {
 		return "", err
 	}
-	oldV := sv.Value
+	// The map s.systems[sv.Name] is lazy initialized. If we directly read it, we might read empty result.
+	// Since this code path is not a hot path, we directly call GetSessionOrGlobalSystemVar to get the value safely.
+	oldV, err := s.GetSessionOrGlobalSystemVar(context.Background(), sv.Name)
+	if err != nil {
+		return "", err
+	}
 	return oldV, sv.SetSessionFromHook(s, val)
 }
 

diff --git a/sessionctx/variable/setvar_test.go b/sessionctx/variable/setvar_test.go
@@ -110,6 +110,26 @@ func TestSetVarNonStringOrEnum(t *testing.T) {
 			tk.MustQuery(fmt.Sprintf("select @@%v", c.varName)).Check(r)
 		}
 	}
+
+	tk.MustQuery("select @@max_execution_time").Check(testkit.Rows("0"))
+	tk.MustExec("set @@max_execution_time=1000")
+	tk.MustQuery("select @@max_execution_time").Check(testkit.Rows("1000"))
+	tk.MustQuery("select /*+ set_var(max_execution_time=100) */ @@max_execution_time").Check(testkit.Rows("100"))
+	// The value is the changed value 1000, not the default value 0.
+	tk.MustQuery("select @@max_execution_time").Check(testkit.Rows("1000"))
+
+	tk.MustExec("set @@global.max_execution_time=1000")
+
+	tk2 := testkit.NewTestKit(t, store)
+	tk2.MustQuery("select @@max_execution_time").Check(testkit.Rows("1000"))
+	tk2.MustQuery("select /*+ set_var(max_execution_time=100) */ @@max_execution_time").Check(testkit.Rows("100"))
+	// The value is the global value 1000, not the default value 0.
+	tk2.MustQuery("select @@max_execution_time").Check(testkit.Rows("1000"))
+	tk2.MustExec("set @@max_execution_time=2000")
+	tk2.MustQuery("select @@max_execution_time").Check(testkit.Rows("2000"))
+	tk2.MustQuery("select /*+ set_var(max_execution_time=100) */ @@max_execution_time").Check(testkit.Rows("100"))
+	// The value is the changed value 2000, not the default value 0 or the global value 1000.
+	tk2.MustQuery("select @@max_execution_time").Check(testkit.Rows("2000"))
 }
 
 func TestSetVarStringOrEnum(t *testing.T) {