plan: fix a bug when expectedCnt and count after filter are all 0. (p…

…ingcap#5947)
doerjiayi · Mar 8, 2018 · 73900c4 · 73900c4
1 parent d3186dc
commit 73900c4
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Showing 3 changed files with 21 additions and 3 deletions.
diff --git a/plan/cbo_test.go b/plan/cbo_test.go
@@ -118,7 +118,7 @@ func (s *testAnalyzeSuite) TestIndexRead(c *C) {
 		store.Close()
 	}()
 	testKit.MustExec("use test")
-	testKit.MustExec("drop table if exists t")
+	testKit.MustExec("drop table if exists t, t1")
 	testKit.MustExec("create table t (a int primary key, b int, c varchar(200), d datetime DEFAULT CURRENT_TIMESTAMP, e int, ts timestamp DEFAULT CURRENT_TIMESTAMP)")
 	testKit.MustExec("create index b on t (b)")
 	testKit.MustExec("create index d on t (d)")
@@ -128,7 +128,12 @@ func (s *testAnalyzeSuite) TestIndexRead(c *C) {
 	for i := 0; i < 100; i++ {
 		testKit.MustExec(constructInsertSQL(i, 100))
 	}
+	testKit.MustExec("create table t1 (a int, b int, index idx(a), index idxx(b))")
+	for i := 1; i < 16; i++ {
+		testKit.MustExec(fmt.Sprintf("insert into t1 values(%v, %v)", i, i))
+	}
 	testKit.MustExec("analyze table t")
+	testKit.MustExec("analyze table t1")
 	tests := []struct {
 		sql  string
 		best string
@@ -208,6 +213,10 @@ func (s *testAnalyzeSuite) TestIndexRead(c *C) {
 			sql:  "select * from t where ts < '1991-09-05'",
 			best: "IndexLookUp(Index(t.ts)[[-inf,1991-09-05 00:00:00)], Table(t))",
 		},
+		{
+			sql:  "select sum(a) from t1 use index(idx) where a = 3 and b = 100000 group by a limit 1",
+			best: "IndexLookUp(Index(t1.idx)[[3,3]], Table(t1)->Sel([eq(test.t1.b, 100000)]))->StreamAgg->Limit",
+		},
 	}
 	for _, tt := range tests {
 		ctx := testKit.Se.(sessionctx.Context)

diff --git a/plan/gen_physical_plans.go b/plan/gen_physical_plans.go
@@ -551,6 +551,9 @@ func (la *LogicalAggregation) getStreamAggs(prop *requiredProp) []PhysicalPlan {
 				desc:        prop.desc,
 				expectedCnt: prop.expectedCnt * la.inputCount / la.stats.count,
 			}
+			if childProp.expectedCnt < prop.expectedCnt {
+				childProp.expectedCnt = prop.expectedCnt
+			}
 			if !prop.isPrefix(childProp) {
 				continue
 			}

diff --git a/plan/physical_plan_builder.go b/plan/physical_plan_builder.go
@@ -354,7 +354,10 @@ func (ds *DataSource) convertToIndexScan(prop *requiredProp, idx *model.IndexInf
 			}
 		}
 	}
-	if matchProperty && prop.expectedCnt < math.MaxFloat64 {
+	// Only use expectedCnt when it's smaller than the count we calculated.
+	// e.g. IndexScan(count1)->After Filter(count2). The `ds.statsAfterSelect.count` is count2. count1 is the one we need to calculate
+	// If expectedCnt and count2 are both zero and we go into the below `if` block, the count1 will be set to zero though it's shouldn't be.
+	if matchProperty && prop.expectedCnt < ds.statsAfterSelect.count {
 		selectivity, err := statsTbl.Selectivity(ds.ctx, is.filterCondition)
 		if err != nil {
 			log.Warnf("An error happened: %v, we have to use the default selectivity", err.Error())
@@ -572,7 +575,10 @@ func (ds *DataSource) convertToTableScan(prop *requiredProp) (task task, err err
 	}
 	task = copTask
 	matchProperty := len(prop.cols) == 1 && pkCol != nil && prop.cols[0].Equal(nil, pkCol)
-	if matchProperty && prop.expectedCnt < math.MaxFloat64 {
+	// Only use expectedCnt when it's smaller than the count we calculated.
+	// e.g. IndexScan(count1)->After Filter(count2). The `ds.statsAfterSelect.count` is count2. count1 is the one we need to calculate
+	// If expectedCnt and count2 are both zero and we go into the below `if` block, the count1 will be set to zero though it's shouldn't be.
+	if matchProperty && prop.expectedCnt < ds.statsAfterSelect.count {
 		selectivity, err := statsTbl.Selectivity(ds.ctx, ts.filterCondition)
 		if err != nil {
 			log.Warnf("An error happened: %v, we have to use the default selectivity", err.Error())