region: check if the query startkey and endkey specify an uncovered region

pkg/core/region.go

@@ -1789,7 +1789,42 @@ func (r *RegionsInfo) GetRegionCount(startKey, endKey []byte) int {
 	defer r.t.RUnlock()
 	start := &regionItem{&RegionInfo{meta: &metapb.Region{StartKey: startKey}}}
 	end := &regionItem{&RegionInfo{meta: &metapb.Region{StartKey: endKey}}}
-	// it returns 0 if startKey is nil.
+
+	// check if both keys are in the uncovered ranges.
+	startItem, sit := r.tree.tree.GetWithIndex(start)
+	endItem, eit := r.tree.tree.GetWithIndex(end)
+	if startItem == nil {
+		startItem = r.tree.tree.GetAt(sit - 1)
+	} else {
+		sit += 1
+	}
+	if endItem == nil {
+		endItem = r.tree.tree.GetAt(eit - 1)
+	} else {
+		eit += 1
+	}
+
+	startInAnInterval := false
+	if startItem != nil {
+		startInAnInterval = (bytes.Compare(startItem.GetStartKey(), startKey) <= 0) && (bytes.Compare(startKey, startItem.GetEndKey()) <= 0)
+	}
+	endInAnInterval := false
+	if endItem != nil {
+		endInAnInterval = (bytes.Compare(endItem.GetStartKey(), endKey) <= 0) && (bytes.Compare(endKey, endItem.GetEndKey()) <= 0)
+	}
+
+	if len(endKey) == 0 {
+		endItem = r.tree.tree.GetAt(r.tree.tree.Len() - 1)
+		eit = r.tree.tree.Len()
+		endInAnInterval = false
+		if endItem != nil {
+			endInAnInterval = (bytes.Compare(endItem.GetEndKey(), endKey) <= 0) && (bytes.Compare(endKey, endItem.GetEndKey()) <= 0)
+		}
+	}
+	if sit == eit && (!startInAnInterval) && (!endInAnInterval) {
+		return 0
+	}
+
 	_, startIndex := r.tree.tree.GetWithIndex(start)
 	var endIndex int
 	var item *regionItem

server/api/stats_test.go

@@ -20,6 +20,7 @@ import (
 	"testing"
 
 	"github.com/pingcap/kvproto/pkg/metapb"
+	"github.com/stretchr/testify/require"
 	"github.com/stretchr/testify/suite"
 	"github.com/tikv/pd/pkg/core"
 	"github.com/tikv/pd/pkg/statistics"
@@ -204,3 +205,99 @@ func (suite *statsTestSuite) TestRegionStats() {
 		}
 	}
 }
+
+func TestRegionStatsHoles(t *testing.T) {
+	re := require.New(t)
+	svr, cleanup := mustNewServer(re)
+	defer cleanup()
+	server.MustWaitLeader(re, []*server.Server{svr})
+
+	addr := svr.GetAddr()
+	urlPrefix := fmt.Sprintf("%s%s/api/v1", addr, apiPrefix)
+
+	mustBootstrapCluster(re, svr)
+
+	statsURL := urlPrefix + "/stats/region"
+	epoch := &metapb.RegionEpoch{
+		ConfVer: 1,
+		Version: 1,
+	}
+
+	// range holes
+	regionsWithholes := []*core.RegionInfo{
+		core.NewRegionInfo(
+			&metapb.Region{
+				Id:       1,
+				StartKey: []byte("-"),
+				EndKey:   []byte("c"),
+				Peers: []*metapb.Peer{
+					{Id: 101, StoreId: 1},
+					{Id: 102, StoreId: 2},
+					{Id: 103, StoreId: 3},
+				},
+				RegionEpoch: epoch,
+			},
+			&metapb.Peer{Id: 101, StoreId: 1},
+			core.SetApproximateSize(100),
+			core.SetApproximateKvSize(80),
+			core.SetApproximateKeys(50),
+		),
+		core.NewRegionInfo(
+			&metapb.Region{
+				Id:       2,
+				StartKey: []byte("g"),
+				EndKey:   []byte("l"),
+				Peers: []*metapb.Peer{
+					{Id: 104, StoreId: 1},
+					{Id: 105, StoreId: 4},
+					{Id: 106, StoreId: 5},
+				},
+				RegionEpoch: epoch,
+			},
+			&metapb.Peer{Id: 105, StoreId: 4},
+			core.SetApproximateSize(200),
+			core.SetApproximateKvSize(180),
+			core.SetApproximateKeys(150),
+		),
+		core.NewRegionInfo(
+			&metapb.Region{
+				Id:       3,
+				StartKey: []byte("o"),
+				EndKey:   []byte("u"),
+				Peers: []*metapb.Peer{
+					{Id: 106, StoreId: 1},
+					{Id: 107, StoreId: 5},
+				},
+				RegionEpoch: epoch,
+			},
+			&metapb.Peer{Id: 107, StoreId: 5},
+			core.SetApproximateSize(1),
+			core.SetApproximateKvSize(1),
+			core.SetApproximateKeys(1),
+		),
+	}
+
+	for _, r := range regionsWithholes {
+		mustRegionHeartbeat(re, svr, r)
+	}
+
+	// holes in between :
+	// | - c| ... |g - l| ... |o - u| ...
+
+	startKeys := [6]string{"d", "b", "b", "i", "", "v"}
+	endKeys := [6]string{"e", "e", "i", "j", "", ""}
+	ans := [6]int{0, 1, 2, 1, 3, 0}
+
+	for i := range startKeys {
+		startKey := url.QueryEscape(startKeys[i])
+		endKey := url.QueryEscape(endKeys[i])
+		argsWithHoles := fmt.Sprintf("?start_key=%s&end_key=%s&count", startKey, endKey)
+		res, err := testDialClient.Get(statsURL + argsWithHoles)
+		re.NoError(err)
+		stats := &statistics.RegionStats{}
+		err = apiutil.ReadJSON(res.Body, stats)
+		res.Body.Close()
+		re.NoError(err)
+		re.Equal(ans[i], stats.Count)
+	}
+}