cherry pick pingcap#22101 to release-5.0-rc

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

session/session.go

@@ -1115,16 +1115,20 @@ func (s *session) SetProcessInfo(sql string, t time.Time, command byte, maxExecu
 		MaxExecutionTime: maxExecutionTime,
 		RedactSQL:        s.sessionVars.EnableRedactLog,
 	}
+	oldPi := s.ShowProcess()
 	if p == nil {
 		// Store the last valid plan when the current plan is nil.
 		// This is for `explain for connection` statement has the ability to query the last valid plan.
-		oldPi := s.ShowProcess()
 		if oldPi != nil && oldPi.Plan != nil && len(oldPi.PlanExplainRows) > 0 {
 			pi.Plan = oldPi.Plan
 			pi.PlanExplainRows = oldPi.PlanExplainRows
 			pi.RuntimeStatsColl = oldPi.RuntimeStatsColl
 		}
 	}
+	// We set process info before building plan, so we extended execution time.
+	if oldPi != nil && oldPi.Info == pi.Info {
+		pi.Time = oldPi.Time
+	}
 	_, pi.Digest = s.sessionVars.StmtCtx.SQLDigest()
 	// DO NOT reset the currentPlan to nil until this query finishes execution, otherwise reentrant calls
 	// of SetProcessInfo would override Plan and PlanExplainRows to nil.
@@ -1227,6 +1231,10 @@ func (s *session) ExecuteStmt(ctx context.Context, stmtNode ast.StmtNode) (sqlex
 		return nil, err
 	}
 
+	// Uncorrelated subqueries will execute once when building plan, so we reset process info before building plan.
+	cmd32 := atomic.LoadUint32(&s.GetSessionVars().CommandValue)
+	s.SetProcessInfo(stmtNode.Text(), time.Now(), byte(cmd32), 0)
+
 	// Transform abstract syntax tree to a physical plan(stored in executor.ExecStmt).
 	compiler := executor.Compiler{Ctx: s}
 	stmt, err := compiler.Compile(ctx, stmtNode)

session/session_test.go

@@ -3830,3 +3830,39 @@ func (s *testSessionSerialSuite) TestDefaultWeekFormat(c *C) {
 	tk2 := testkit.NewTestKitWithInit(c, s.store)
 	tk2.MustQuery("select week('2020-02-02'), @@default_week_format, week('2020-02-02');").Check(testkit.Rows("6 4 6"))
 }
+<<<<<<< HEAD
+=======
+
+func (s *testSessionSerialSuite) TestIssue21944(c *C) {
+	tk1 := testkit.NewTestKitWithInit(c, s.store)
+	_, err := tk1.Exec("set @@tidb_current_ts=1;")
+	c.Assert(err.Error(), Equals, "[variable:1238]Variable 'tidb_current_ts' is a read only variable")
+}
+
+func (s *testSessionSerialSuite) TestIssue21943(c *C) {
+	tk := testkit.NewTestKitWithInit(c, s.store)
+	_, err := tk.Exec("set @@last_plan_from_binding='123';")
+	c.Assert(err.Error(), Equals, "[variable:1238]Variable 'last_plan_from_binding' is a read only variable")
+
+	_, err = tk.Exec("set @@last_plan_from_cache='123';")
+	c.Assert(err.Error(), Equals, "[variable:1238]Variable 'last_plan_from_cache' is a read only variable")
+}
+
+func (s *testSessionSerialSuite) TestProcessInfoIssue22068(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t(a int)")
+	wg := sync.WaitGroup{}
+	wg.Add(1)
+	go func() {
+		tk.MustQuery("select 1 from t where a = (select sleep(5));").Check(testkit.Rows())
+		wg.Done()
+	}()
+	time.Sleep(2 * time.Second)
+	pi := tk.Se.ShowProcess()
+	c.Assert(pi, NotNil)
+	c.Assert(pi.Info, Equals, "select 1 from t where a = (select sleep(5));")
+	c.Assert(pi.Plan, IsNil)
+	wg.Wait()
+}
+>>>>>>> 57cd69473... session: set process info before building plan (#22101)