planner: process over-optimization and skip plan-cache in some cases to avoid disaster plans

executor/explainfor_test.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"math"
 	"strconv"
+	"strings"
 	"sync"
 
 	. "github.com/pingcap/check"
@@ -958,7 +959,7 @@ 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"))
 
@@ -1527,3 +1528,28 @@ func (s *testSuite) TestIssue28792(c *C) {
 	r2 := tk.MustQuery("EXPLAIN SELECT t12.a, t12.b FROM t12 LEFT JOIN t97 use index () on t12.b = t97.b;").Rows()
 	c.Assert(r1, DeepEquals, r2)
 }
+
+func (s *testSuite) TestIssue38533(c *C) {
+	store, dom, err := newStoreWithBootstrap()
+	c.Assert(err, IsNil)
+	defer func() {
+		dom.Close()
+		store.Close()
+	}()
+	tk := testkit.NewTestKit(c, 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.Se.ShowProcess()
+	ps := []*util.ProcessInfo{tkProcess}
+	tk.Se.SetSessionManager(&mockSessionManager1{PS: ps})
+	plan := tk.MustQuery(fmt.Sprintf("explain for connection %d", tkProcess.ID)).Rows()
+	c.Assert(strings.Contains(plan[1][0].(string), "RangeScan"), IsTrue) // 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"))
+}

planner/core/prepare_test.go

@@ -1520,7 +1520,7 @@ 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) {
@@ -2037,11 +2037,10 @@ func (s *testPlanSerialSuite) TestPlanCachePointGetAndTableDual(c *C) {
 	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')")
@@ -2057,11 +2056,10 @@ func (s *testPlanSerialSuite) TestPlanCachePointGetAndTableDual(c *C) {
 	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")
@@ -2078,7 +2076,7 @@ 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")) // 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")
@@ -2171,7 +2169,7 @@ 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")) // b>=1 and b<=1 --> b=1
 }
 
 func (s *testPrepareSerialSuite) TestIssue29296(c *C) {

util/ranger/detacher.go

@@ -504,7 +504,9 @@ func extractValueInfo(expr expression.Expression) *valueInfo {
 // accesses: The condition will be used to build range.
 // filters: filters is the part that some access conditions need to be evaluate again since it's only the prefix part of char column.
 // newConditions: We'll simplify the given conditions if there're multiple in conditions or eq conditions on the same column.
-//   e.g. if there're a in (1, 2, 3) and a in (2, 3, 4). This two will be combined to a in (2, 3) and pushed to newConditions.
+//
+//	e.g. if there're a in (1, 2, 3) and a in (2, 3, 4). This two will be combined to a in (2, 3) and pushed to newConditions.
+//
 // columnValues: the constant column values for all index columns. columnValues[i] is nil if cols[i] is not constant.
 // bool: indicate whether there's nil range when merging eq and in conditions.
 func ExtractEqAndInCondition(sctx sessionctx.Context, conditions []expression.Expression, cols []*expression.Column,
@@ -577,8 +579,7 @@ 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
+				sctx.GetSessionVars().StmtCtx.SkipPlanCache = true
 			}
 		}
 	}