sessionctx, executor: fix failure of reading MaxPreparedStmtCount

executor/prepared_test.go

@@ -23,6 +23,7 @@ import (
  "github.com/pingcap/tidb/parser/auth"
  "github.com/pingcap/tidb/parser/model"
  "github.com/pingcap/tidb/parser/mysql"
+ "github.com/pingcap/tidb/parser/terror"
  plannercore "github.com/pingcap/tidb/planner/core"
  "github.com/pingcap/tidb/server"
  "github.com/pingcap/tidb/sessionctx/variable"
@@ -1255,3 +1256,13 @@ func TestIssue31141(t *testing.T) {
  tk.MustExec("set @@tidb_txn_mode = 'optimistic'")
  tk.MustExec("prepare stmt1 from 'do 1'")
 }
+
+func TestMaxPreparedStmtCount(t *testing.T) {
+ store := testkit.CreateMockStore(t)
+ tk := testkit.NewTestKit(t, store)
+ tk.MustExec("set @@global.max_prepared_stmt_count = 2")
+ tk.MustExec("prepare stmt1 from 'select ? as num from dual'")
+ tk.MustExec("prepare stmt2 from 'select ? as num from dual'")
+ err := tk.ExecToErr("prepare stmt3 from 'select ? as num from dual'")
+ require.True(t, terror.ErrorEqual(err, variable.ErrMaxPreparedStmtCountReached))
+}

sessionctx/variable/session.go

@@ -2097,11 +2097,7 @@ func (s *SessionVars) GetNonPreparedPlanCacheStmt(sql string) interface{} {
 // AddPreparedStmt adds prepareStmt to current session and count in global.
 func (s *SessionVars) AddPreparedStmt(stmtID uint32, stmt interface{}) error {
  if _, exists := s.PreparedStmts[stmtID]; !exists {
- valStr, _ := s.GetSystemVar(MaxPreparedStmtCount)
- maxPreparedStmtCount, err := strconv.ParseInt(valStr, 10, 64)
- if err != nil {
- maxPreparedStmtCount = DefMaxPreparedStmtCount
- }
+ maxPreparedStmtCount := MaxPreparedStmtCountValue.Load()
  newPreparedStmtCount := atomic.AddInt64(&PreparedStmtCount, 1)
  if maxPreparedStmtCount >= 0 && newPreparedStmtCount > maxPreparedStmtCount {
  atomic.AddInt64(&PreparedStmtCount, -1)

sessionctx/variable/sysvar.go

@@ -479,7 +479,15 @@ var defaultSysVars = []*SysVar{
  }},
 
  /* The system variables below have GLOBAL scope */
- {Scope: ScopeGlobal, Name: MaxPreparedStmtCount, Value: strconv.FormatInt(DefMaxPreparedStmtCount, 10), Type: TypeInt, MinValue: -1, MaxValue: 1048576},
+ {Scope: ScopeGlobal, Name: MaxPreparedStmtCount, Value: strconv.FormatInt(DefMaxPreparedStmtCount, 10), Type: TypeInt, MinValue: -1, MaxValue: 1048576,
+ SetGlobal: func(_ context.Context, s *SessionVars, val string) error {
+ num, err := strconv.ParseInt(val, 10, 64)
+ if err != nil {
+ return errors.Trace(err)
+ }
+ MaxPreparedStmtCountValue.Store(num)
+ return nil
+ }},
  {Scope: ScopeGlobal, Name: InitConnect, Value: "", Validation: func(vars *SessionVars, normalizedValue string, originalValue string, scope ScopeFlag) (string, error) {
  p := parser.New()
  p.SetSQLMode(vars.SQLMode)

sessionctx/variable/tidb_vars.go

@@ -1236,6 +1236,7 @@ var (
  PasswordHistory = atomic.NewInt64(DefPasswordReuseHistory)
  PasswordReuseInterval = atomic.NewInt64(DefPasswordReuseTime)
  IsSandBoxModeEnabled = atomic.NewBool(false)
+ MaxPreparedStmtCountValue = atomic.NewInt64(DefMaxPreparedStmtCount)
  HistoricalStatsDuration = atomic.NewDuration(DefTiDBHistoricalStatsDuration)
 )