planner: allow to use dynamic mode to access partitioning tables without global-stats (#44264)

close pingcap/tidb#44262

planner/core/casetest/integration_test.go

@@ -3513,3 +3513,32 @@ func TestFixControl(t *testing.T) {
 		require.Equal(t, output[i].Variable, rows)
 	}
 }
+
+func TestFixControl44262(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec(`use test`)
+	tk.MustExec(`set tidb_partition_prune_mode='dynamic'`)
+	tk.MustExec(`create table t1 (a int, b int)`)
+	tk.MustExec(`create table t2_part (a int, b int, key(a)) partition by hash(a) partitions 4`)
+
+	testJoin := func(q, join string) {
+		found := false
+		for _, x := range tk.MustQuery(`explain ` + q).Rows() {
+			if strings.Contains(x[0].(string), join) {
+				found = true
+			}
+		}
+		if !found {
+			t.Fatal(q, join)
+		}
+	}
+
+	testJoin(`select /*+ TIDB_INLJ(t2_part@sel_2) */ * from t1 where t1.b<10 and not exists (select 1 from t2_part where t1.a=t2_part.a and t2_part.b<20)`, "HashJoin")
+	tk.MustQuery(`show warnings`).Sort().Check(testkit.Rows(
+		`Warning 1105 disable dynamic pruning due to t2_part has no global stats`,
+		`Warning 1815 Optimizer Hint /*+ INL_JOIN(t2_part) */ or /*+ TIDB_INLJ(t2_part) */ is inapplicable`))
+	tk.MustExec(`set @@tidb_opt_fix_control = "44262:ON"`)
+	testJoin(`select /*+ TIDB_INLJ(t2_part@sel_2) */ * from t1 where t1.b<10 and not exists (select 1 from t2_part where t1.a=t2_part.a and t2_part.b<20)`, "IndexJoin")
+	tk.MustQuery(`show warnings`).Sort().Check(testkit.Rows()) // no warning
+}

planner/core/logical_plan_builder.go

@@ -4584,8 +4584,14 @@ func (b *PlanBuilder) buildDataSource(ctx context.Context, tn *ast.TableName, as
 				tblStats := h.GetTableStats(tableInfo)
 				isDynamicEnabled := b.ctx.GetSessionVars().IsDynamicPartitionPruneEnabled()
 				globalStatsReady := tblStats.IsInitialized()
+				allowDynamicWithoutStats := false
+				fixValue, ok := b.ctx.GetSessionVars().GetOptimizerFixControlValue(variable.TiDBOptFixControl44262)
+				if ok && variable.TiDBOptOn(fixValue) {
+					allowDynamicWithoutStats = true
+				}
+
 				// If dynamic partition prune isn't enabled or global stats is not ready, we won't enable dynamic prune mode in query
-				usePartitionProcessor := !isDynamicEnabled || !globalStatsReady
+				usePartitionProcessor := !isDynamicEnabled || (!globalStatsReady && !allowDynamicWithoutStats)
 
 				failpoint.Inject("forceDynamicPrune", func(val failpoint.Value) {
 					if val.(bool) {

sessionctx/variable/session.go

@@ -1485,6 +1485,22 @@ type SessionVars struct {
 	HypoIndexes map[string]map[string]map[string]*model.IndexInfo // dbName -> tblName -> idxName -> idxInfo
 }
 
+var (
+	// variables below are for the optimizer fix control.
+
+	// TiDBOptFixControl44262 controls whether to allow to use dynamic-mode to access partitioning tables without global-stats (#44262).
+	TiDBOptFixControl44262 uint64 = 44262
+)
+
+// GetOptimizerFixControlValue returns the specified value of the optimizer fix control.
+func (s *SessionVars) GetOptimizerFixControlValue(key uint64) (value string, exist bool) {
+	if s.OptimizerFixControl == nil {
+		return "", false
+	}
+	value, exist = s.OptimizerFixControl[key]
+	return
+}
+
 // planReplayerSessionFinishedTaskKeyLen is used to control the max size for the finished plan replayer task key in session
 // in order to control the used memory
 const planReplayerSessionFinishedTaskKeyLen = 128