planner: process over-optimization and skip plan-cache in some cases …

…to avoid disaster plans (#38537) (#42627)

close #38533

executor/explainfor_test.go

@@ -958,7 +958,7 @@ func (s *testPrepareSerialSuite) TestIndexMerge4PlanCache(c *C) {
 	tk.MustExec("set @a=9, @b=10, @c=11;")
 	tk.MustQuery("execute stmt using @a, @a;").Check(testkit.Rows("10 10 10"))
 	tk.MustQuery("execute stmt using @a, @c;").Check(testkit.Rows("10 10 10", "11 11 11"))
-	tk.MustQuery("select @@last_plan_from_cache;").Check(testkit.Rows("1"))
+	tk.MustQuery("select @@last_plan_from_cache;").Check(testkit.Rows("0")) // a>=9 and a<=9 --> a=9
 	tk.MustQuery("execute stmt using @c, @a;").Check(testkit.Rows("10 10 10"))
 	tk.MustQuery("select @@last_plan_from_cache;").Check(testkit.Rows("1"))
 

executor/prepared_test.go

@@ -150,6 +150,37 @@ func TestPreparedStmtWithHint(t *testing.T) {
 	require.Equal(t, int32(1), atomic.LoadInt32(&sm.killed))
 }
 
+func TestIssue38533(t *testing.T) {
+	store, dom, err := newStoreWithBootstrap()
+	require.NoError(t, err)
+	defer func() {
+		require.NoError(t, store.Close())
+		dom.Close()
+	}()
+
+	orgEnable := plannercore.PreparedPlanCacheEnabled()
+	defer func() {
+		plannercore.SetPreparedPlanCache(orgEnable)
+	}()
+	plannercore.SetPreparedPlanCache(true)
+	tk := testkit.NewTestKit(t, store)
+
+	tk.MustExec("use test")
+	tk.MustExec("create table t (a int, key (a))")
+	tk.MustExec(`prepare st from "select /*+ use_index(t, a) */ a from t where a=? and a=?"`)
+	tk.MustExec(`set @a=1`)
+	tk.MustExec(`execute st using @a, @a`)
+	tkProcess := tk.Session().ShowProcess()
+	ps := []*util.ProcessInfo{tkProcess}
+	tk.Session().SetSessionManager(&mockSessionManager1{PS: ps})
+	plan := tk.MustQuery(fmt.Sprintf("explain for connection %d", tkProcess.ID)).Rows()
+	require.True(t, strings.Contains(plan[1][0].(string), "RangeScan")) // range-scan instead of full-scan
+
+	tk.MustExec(`execute st using @a, @a`)
+	tk.MustExec(`execute st using @a, @a`)
+	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("0"))
+}
+
 func TestIssue29850(t *testing.T) {
 	store, dom, err := newStoreWithBootstrap()
 	require.NoError(t, err)

planner/core/prepare_test.go

@@ -1521,7 +1521,7 @@ func (s *testPlanSerialSuite) TestIssue29303(c *C) {
 	tk.MustQuery(`execute stmt using @a,@b,@c,@d`).Check(testkit.Rows())
 	tk.MustExec(`set @a="龂", @b="龂", @c="龂", @d="龂"`)
 	tk.MustQuery(`execute stmt using @a,@b,@c,@d`).Check(testkit.Rows("� 龂 � 龂"))
-	tk.MustQuery(`select @@last_plan_from_cache`).Check(testkit.Rows("0"))
+	tk.MustQuery(`select @@last_plan_from_cache`).Check(testkit.Rows("1"))
 }
 
 func (s *testPlanSerialSuite) TestIssue28942(c *C) {
@@ -2068,7 +2068,7 @@ func (s *testPlanSerialSuite) TestPlanCachePointGetAndTableDual(c *C) {
 	tk.MustQuery("execute s1 using @a1, @b1, @b1").Check(testkit.Rows())
 	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("0"))
 	tk.MustQuery("execute s1 using @a1, @a1, @b1").Check(testkit.Rows("0000 7777 1"))
-	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("1"))
+	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("0")) // c2>=9999 and c2<=9999 --> c2=9999
 
 	tk.MustExec("create table t2(c1 bigint(20) primary key, c2 varchar(20))")
 	tk.MustExec("insert into t2 values(1,'7777')")
@@ -2088,7 +2088,7 @@ func (s *testPlanSerialSuite) TestPlanCachePointGetAndTableDual(c *C) {
 	tk.MustQuery("execute s3 using @a3,@a3").Check(testkit.Rows())
 	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("0"))
 	tk.MustQuery("execute s3 using @a3,@b3").Check(testkit.Rows("2 1 1"))
-	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("1"))
+	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("0")) // c1>=1 and c1<=1 --> c1==1
 
 	tk.MustExec("prepare s3 from 'select /*+ use_index_merge(t3) */ * from t3 where (c1 >= ? and c1 <= ?) or c2 > 1'")
 	tk.MustExec("set @a3=1,@b3=3")
@@ -2105,7 +2105,7 @@ func (s *testPlanSerialSuite) TestPlanCachePointGetAndTableDual(c *C) {
 	tk.MustQuery("execute s4 using @a4,@a4").Check(testkit.Rows())
 	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("0"))
 	tk.MustQuery("execute s4 using @a4,@b4").Check(testkit.Rows("2 1 1"))
-	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("1"))
+	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("0"))
 
 	tk.MustExec("prepare s4 from 'select /*+ use_index_merge(t4) */ * from t4 where (c1 >= ? and c1 <= ?) or c2 > 1'")
 	tk.MustExec("set @a4=1,@b4=3")
@@ -2198,7 +2198,7 @@ func (s *testPlanSerialSuite) TestIssue23671(c *C) {
 	tk.MustQuery("execute s1 using @a, @b, @c").Check(testkit.Rows("1 1"))
 	tk.MustExec("set @a=1, @b=1, @c=10")
 	tk.MustQuery("execute s1 using @a, @b, @c").Check(testkit.Rows("1 1", "2 2"))
-	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("1"))
+	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("0"))
 }
 
 func (s *testPrepareSerialSuite) TestIssue29296(c *C) {

util/ranger/detacher.go

@@ -577,8 +577,8 @@ func ExtractEqAndInCondition(sctx sessionctx.Context, conditions []expression.Ex
 				columnValues[i] = &valueInfo{mutable: true}
 			}
 			if expression.MaybeOverOptimized4PlanCache(sctx, conditions) {
-				// TODO: optimize it more elaborately, e.g. return [2 3, 2 3] as accesses for 'where a = 2 and b = 3 and c >= ? and c <= ?'
-				return nil, conditions, nil, nil, false
+				// `a=@x and a=@y` --> `a=@x if @x==@y`
+				sctx.GetSessionVars().StmtCtx.SkipPlanCache = true
 			}
 		}
 	}