lightning: split and scatter regions in batches

br/pkg/lightning/backend/local/local.go

@@ -91,6 +91,8 @@ const (
 	// lower the max-key-count to avoid tikv trigger region auto split
 	regionMaxKeyCount      = 1_280_000
 	defaultRegionSplitSize = 96 * units.MiB
+	// The max ranges count in a batch to split and scatter.
+	maxBatchSplitRanges = 4096
 
 	propRangeIndex = "tikv.range_index"
 
@@ -1357,7 +1359,7 @@ func (local *local) ImportEngine(ctx context.Context, engineUUID uuid.UUID, regi
 		needSplit := len(unfinishedRanges) > 1 || lfTotalSize > regionSplitSize || lfLength > regionSplitKeys
 		// split region by given ranges
 		for i := 0; i < maxRetryTimes; i++ {
-			err = local.SplitAndScatterRegionByRanges(ctx, unfinishedRanges, lf.tableInfo, needSplit, regionSplitSize)
+			err = local.SplitAndScatterRegionInBatches(ctx, unfinishedRanges, lf.tableInfo, needSplit, regionSplitSize, maxBatchSplitRanges)
 			if err == nil || common.IsContextCanceledError(err) {
 				break
 			}

br/pkg/lightning/backend/local/localhelper.go

@@ -59,10 +59,32 @@ var (
 	splitRetryTimes = 8
 )
 
-// TODO remove this file and use br internal functions
-// This File include region split & scatter operation just like br.
+// SplitAndScatterRegionInBatches splits&scatter regions in batches.
+// Too many split&scatter requests may put a lot of pressure on TiKV and PD.
+func (local *local) SplitAndScatterRegionInBatches(
+	ctx context.Context,
+	ranges []Range,
+	tableInfo *checkpoints.TidbTableInfo,
+	needSplit bool,
+	regionSplitSize int64,
+	batchCnt int,
+) error {
+	for i := 0; i < len(ranges); i += batchCnt {
+		batch := ranges[i:]
+		if len(batch) > batchCnt {
+			batch = batch[:batchCnt]
+		}
+		if err := local.SplitAndScatterRegionByRanges(ctx, batch, tableInfo, needSplit, regionSplitSize); err != nil {
+			return errors.Trace(err)
+		}
+	}
+	return nil
+}
+
+// SplitAndScatterRegionByRanges include region split & scatter operation just like br.
 // we can simply call br function, but we need to change some function signature of br
 // When the ranges total size is small, we can skip the split to avoid generate empty regions.
+// TODO: remove this file and use br internal functions
 func (local *local) SplitAndScatterRegionByRanges(
 	ctx context.Context,
 	ranges []Range,
@@ -428,9 +450,15 @@ func (local *local) waitForScatterRegion(ctx context.Context, regionInfo *split.
 	for i := 0; i < split.ScatterWaitMaxRetryTimes; i++ {
 		ok, err := local.isScatterRegionFinished(ctx, regionID)
 		if err != nil {
-			log.L().Warn("scatter region failed: do not have the region",
-				logutil.Region(regionInfo.Region))
-			return
+			log.L().Warn(
+				"wait for scatter region failed, will scatter again",
+				logutil.Region(regionInfo.Region),
+				zap.Error(err),
+			)
+			if err := local.splitCli.ScatterRegion(ctx, regionInfo); err != nil {
+				log.L().Warn("scatter region failed", zap.Error(err))
+			}
+			continue
 		}
 		if ok {
 			break
@@ -462,9 +490,18 @@ func (local *local) isScatterRegionFinished(ctx context.Context, regionID uint64
 		return false, errors.Errorf("get operator error: %s", respErr.GetType())
 	}
 	// If the current operator of the region is not 'scatter-region', we could assume
-	// that 'scatter-operator' has finished or timeout
-	ok := string(resp.GetDesc()) != "scatter-region" || resp.GetStatus() != pdpb.OperatorStatus_RUNNING
-	return ok, nil
+	// that 'scatter-operator' has finished.
+	if string(resp.GetDesc()) != "scatter-region" {
+		return true, nil
+	}
+	switch resp.GetStatus() {
+	case pdpb.OperatorStatus_RUNNING:
+		return false, nil
+	case pdpb.OperatorStatus_SUCCESS:
+		return true, nil
+	default:
+		return false, errors.Errorf("operator status is %v", resp.GetStatus())
+	}
 }
 
 func getSplitKeysByRanges(ranges []Range, regions []*split.RegionInfo) map[uint64][][]byte {

br/pkg/lightning/backend/local/localhelper_test.go

@@ -17,6 +17,7 @@ package local
 import (
 	"bytes"
 	"context"
+	"fmt"
 	"math"
 	"math/rand"
 	"sort"
@@ -302,7 +303,8 @@ func cloneRegion(region *restore.RegionInfo) *restore.RegionInfo {
 	return &restore.RegionInfo{Region: r, Leader: l}
 }
 
-// region: [, aay), [aay, bba), [bba, bbh), [bbh, cca), [cca, )
+// For keys ["", "aay", "bba", "bbh", "cca", ""], the key ranges of
+// regions are [, aay), [aay, bba), [bba, bbh), [bbh, cca), [cca, ).
 func initTestClient(keys [][]byte, hook clientHook) *testClient {
 	peers := make([]*metapb.Peer, 1)
 	peers[0] = &metapb.Peer{
@@ -574,6 +576,44 @@ func TestBatchSplitByRangesNoValidKeys(t *testing.T) {
 	doTestBatchSplitRegionByRanges(context.Background(), t, &splitRegionNoValidKeyHook{returnErrTimes: math.MaxInt32}, "no valid key", defaultHook{})
 }
 
+func TestSplitAndScatterRegionInBatches(t *testing.T) {
+	splitHook := defaultHook{}
+	deferFunc := splitHook.setup(t)
+	defer deferFunc()
+
+	keys := [][]byte{[]byte(""), []byte("a"), []byte("b"), []byte("")}
+	client := initTestClient(keys, nil)
+	local := &local{
+		splitCli: client,
+		g:        glue.NewExternalTiDBGlue(nil, mysql.ModeNone),
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	var ranges []Range
+	for i := 0; i < 20; i++ {
+		ranges = append(ranges, Range{
+			start: []byte(fmt.Sprintf("a%02d", i)),
+			end:   []byte(fmt.Sprintf("a%02d", i+1)),
+		})
+	}
+
+	err := local.SplitAndScatterRegionInBatches(ctx, ranges, nil, true, 1000, 4)
+	require.NoError(t, err)
+
+	rangeStart := codec.EncodeBytes([]byte{}, []byte("a"))
+	rangeEnd := codec.EncodeBytes([]byte{}, []byte("b"))
+	regions, err := restore.PaginateScanRegion(ctx, client, rangeStart, rangeEnd, 5)
+	require.NoError(t, err)
+	result := [][]byte{[]byte("a"), []byte("a00"), []byte("a01"), []byte("a02"), []byte("a03"), []byte("a04"),
+		[]byte("a05"), []byte("a06"), []byte("a07"), []byte("a08"), []byte("a09"), []byte("a10"), []byte("a11"),
+		[]byte("a12"), []byte("a13"), []byte("a14"), []byte("a15"), []byte("a16"), []byte("a17"), []byte("a18"),
+		[]byte("a19"), []byte("a20"), []byte("b"),
+	}
+	checkRegionRanges(t, regions, result)
+}
+
 type reportAfterSplitHook struct {
 	noopHook
 	ch chan<- struct{}