tidb: do not add history for read-only statements. (#5660)

new_session_test.go

@@ -349,6 +349,24 @@ func (s *testSessionSuite) TestRetryCleanTxn(c *C) {
 	c.Assert(tk.Se.GetSessionVars().InTxn(), IsFalse)
 }
 
+func (s *testSessionSuite) TestReadOnlyNotInHistory(c *C) {
+	tk := testkit.NewTestKitWithInit(c, s.store)
+	tk.MustExec("create table history (a int)")
+	tk.MustExec("insert history values (1), (2), (3)")
+	tk.MustExec("set @@autocommit = 0")
+	tk.MustQuery("select * from history")
+	history := tidb.GetHistory(tk.Se)
+	c.Assert(history.Count(), Equals, 0)
+
+	tk.MustExec("insert history values (4)")
+	tk.MustExec("insert history values (5)")
+	c.Assert(history.Count(), Equals, 2)
+	tk.MustExec("commit")
+	tk.MustQuery("select * from history")
+	history = tidb.GetHistory(tk.Se)
+	c.Assert(history.Count(), Equals, 0)
+}
+
 // TestTruncateAlloc tests that the auto_increment ID does not reuse the old table's allocator.
 func (s *testSessionSuite) TestTruncateAlloc(c *C) {
 	tk := testkit.NewTestKitWithInit(c, s.store)

session.go

@@ -114,6 +114,11 @@ func (h *StmtHistory) Add(stmtID uint32, st ast.Statement, stmtCtx *variable.Sta
 	h.history = append(h.history, s)
 }
 
+// Count returns the count of the history.
+func (h *StmtHistory) Count() int {
+	return len(h.history)
+}
+
 type session struct {
 	// processInfo is used by ShowProcess(), and should be modified atomically.
 	processInfo atomic.Value

tidb.go

@@ -159,7 +159,9 @@ func runStmt(ctx context.Context, s ast.Statement) (ast.RecordSet, error) {
 	se := ctx.(*session)
 	rs, err = s.Exec(ctx)
 	// All the history should be added here.
-	GetHistory(ctx).Add(0, s, se.sessionVars.StmtCtx)
+	if !s.IsReadOnly() {
+		GetHistory(ctx).Add(0, s, se.sessionVars.StmtCtx)
+	}
 	if !se.sessionVars.InTxn() {
 		if err != nil {
 			log.Info("RollbackTxn for ddl/autocommit error.")