stats: set a min count for auto analyze (#5796)

statistics/update.go

@@ -236,8 +236,11 @@ const (
 	StatsPrompt = "stats"
 )
 
+// AutoAnalyzeMinCnt means if the count of table is less than this value, we needn't do auto analyze.
+var AutoAnalyzeMinCnt int64 = 1000
+
 func needAnalyzeTable(tbl *Table, limit time.Duration) bool {
-	if tbl.ModifyCount == 0 {
+	if tbl.ModifyCount == 0 || tbl.Count < AutoAnalyzeMinCnt {
 		return false
 	}
 	t := time.Unix(0, oracle.ExtractPhysical(tbl.Version)*int64(time.Millisecond))

statistics/update_test.go

@@ -21,6 +21,7 @@ import (
 	"github.com/pingcap/tidb/domain"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/model"
+	"github.com/pingcap/tidb/statistics"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util/testkit"
 	"github.com/pingcap/tidb/util/testleak"
@@ -269,6 +270,11 @@ func (s *testStatsUpdateSuite) TestAutoUpdate(c *C) {
 	testKit.MustExec("use test")
 	testKit.MustExec("create table t (a int)")
 
+	statistics.AutoAnalyzeMinCnt = 0
+	defer func() {
+		statistics.AutoAnalyzeMinCnt = 1000
+	}()
+
 	do := s.do
 	is := do.InfoSchema()
 	tbl, err := is.TableByName(model.NewCIStr("test"), model.NewCIStr("t"))