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

…to avoid disaster plans (#38537) (#40213)

close #38533

executor/explainfor_test.go

@@ -949,7 +949,7 @@ func TestIndexMerge4PlanCache(t *testing.T) {
 	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"))
 

planner/core/prepare_test.go

@@ -36,6 +36,7 @@ import (
 	"github.com/pingcap/tidb/sessionctx/variable"
 	"github.com/pingcap/tidb/testkit"
 	"github.com/pingcap/tidb/types"
+	"github.com/pingcap/tidb/util"
 	"github.com/pingcap/tidb/util/hint"
 	"github.com/pingcap/tidb/util/kvcache"
 	"github.com/prometheus/client_golang/prometheus"
@@ -1583,7 +1584,7 @@ func TestIssue29303(t *testing.T) {
 	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 TestIssue34725(t *testing.T) {
@@ -2218,11 +2219,10 @@ func TestPlanCachePointGetAndTableDual(t *testing.T) {
 	tk.MustExec("insert into t1 values('0000','7777',1)")
 	tk.MustExec("prepare s1 from 'select * from t1 where c1=? and c2>=? and c2<=?'")
 	tk.MustExec("set @a1='0000', @b1='9999'")
-	// IndexLookup plan would be built, we should cache it.
 	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')")
@@ -2238,17 +2238,15 @@ func TestPlanCachePointGetAndTableDual(t *testing.T) {
 	tk.MustExec("insert into t3 values(2,1,1)")
 	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")
-	// TableReader plan would be built, we should cache it.
 	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")
-	// TableReader plan would be built, we should cache it.
 	tk.MustQuery("execute s3 using @b3,@a3").Check(testkit.Rows())
-	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("1"))
+	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"))
 
@@ -2259,7 +2257,7 @@ func TestPlanCachePointGetAndTableDual(t *testing.T) {
 	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")) // c1>=3 and c1<=3 --> c1=3
 
 	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")
@@ -2337,7 +2335,35 @@ func TestIssue23671(t *testing.T) {
 	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")) // b>=1 and b<=1 --> b=1
+}
+
+func TestIssue38533(t *testing.T) {
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+	orgEnable := core.PreparedPlanCacheEnabled()
+	defer core.SetPreparedPlanCache(orgEnable)
+	core.SetPreparedPlanCache(true)
+	se, err := session.CreateSession4TestWithOpt(store, &session.Opt{
+		PreparedPlanCache: kvcache.NewSimpleLRUCache(100, 0.1, math.MaxUint64),
+	})
+	require.NoError(t, err)
+	tk := testkit.NewTestKitWithSession(t, store, se)
+
+	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(&testkit.MockSessionManager{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 TestIssue29296(t *testing.T) {
@@ -2877,7 +2903,7 @@ func TestCachedTable(t *testing.T) {
 	// IndexLookup
 	tk.MustQuery("execute indexLookup using @a, @b").Check(testkit.Rows("2"))
 	require.True(t, lastReadFromCache(tk))
-	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("1"))
+	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("0")) // b>1 and b<3 --> b=2
 
 	// PointGet
 	tk.MustQuery("execute pointGet using @a").Check(testkit.Rows("1"))

util/ranger/detacher.go

@@ -578,8 +578,8 @@ 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
 			}
 		}
 	}