enhance: improve mix compaction performance by removing max segment limitations (#38344)

See #37234

---------

Signed-off-by: Ted Xu <ted.xu@zilliz.com>

configs/milvus.yaml

@@ -682,6 +682,7 @@ dataNode:
     levelZeroBatchMemoryRatio: 0.5 # The minimal memory ratio of free memory for level zero compaction executing in batch mode
     levelZeroMaxBatchSize: -1 # Max batch size refers to the max number of L1/L2 segments in a batch when executing L0 compaction. Default to -1, any value that is less than 1 means no limit. Valid range: >= 1.
     useMergeSort: false # Whether to enable mergeSort mode when performing mixCompaction.
+    maxSegmentMergeSort: 30 # The maximum number of segments to be merged in mergeSort mode.
   gracefulStopTimeout: 1800 # seconds. force stop node without graceful stop
   slot:
     slotCap: 16 # The maximum number of tasks(e.g. compaction, importing) allowed to run concurrently on a datanode

internal/datacoord/compaction_trigger.go

@@ -535,7 +535,7 @@ func (t *compactionTrigger) generatePlans(segments []*SegmentInfo, signal *compa
 	toMerge := newSegmentPacker("merge", smallCandidates)
 	toPack := newSegmentPacker("pack", nonPlannedSegments)
 
-	maxSegs := Params.DataCoordCfg.MaxSegmentToMerge.GetAsInt64()
+	maxSegs := int64(4096) // Deprecate the max segment limit since it is irrelevant in simple compactions.
 	minSegs := Params.DataCoordCfg.MinSegmentToMerge.GetAsInt64()
 	compactableProportion := Params.DataCoordCfg.SegmentCompactableProportion.GetAsFloat()
 	satisfiedSize := int64(float64(expectedSize) * compactableProportion)
@@ -543,16 +543,18 @@ func (t *compactionTrigger) generatePlans(segments []*SegmentInfo, signal *compa
 	maxLeftSize := expectedSize - satisfiedSize
 	expectedExpandedSize := int64(float64(expectedSize) * expantionRate)
 	maxExpandedLeftSize := expectedExpandedSize - satisfiedSize
+	reasons := make([]string, 0)
 	// 1. Merge small segments if they can make a full bucket
 	for {
-		pack, _ := toMerge.pack(expectedSize, maxLeftSize, minSegs, maxSegs)
+		pack, left := toMerge.pack(expectedSize, maxLeftSize, minSegs, maxSegs)
 		if len(pack) == 0 {
 			break
 		}
+		reasons = append(reasons, fmt.Sprintf("merging %d small segments with left size %d", len(pack), left))
 		buckets = append(buckets, pack)
 	}
-	// 2. greedy pick from large segment to small, the goal is to fill each segment to reach 512M
-	// we must ensure all prioritized candidates is in a plan
+
+	// 2. Pack prioritized candidates with small segments
 	// TODO the compaction selection policy should consider if compaction workload is high
 	for {
 		// No limit on the remaining size because we want to pack all prioritized candidates
@@ -560,6 +562,7 @@ func (t *compactionTrigger) generatePlans(segments []*SegmentInfo, signal *compa
 		if len(pack) == 0 {
 			break
 		}
+		reasons = append(reasons, fmt.Sprintf("packing %d prioritized segments", len(pack)))
 		buckets = append(buckets, pack)
 	}
 
@@ -570,6 +573,7 @@ func (t *compactionTrigger) generatePlans(segments []*SegmentInfo, signal *compa
 		if len(pack) == 0 {
 			break
 		}
+		reasons = append(reasons, fmt.Sprintf("packing all %d small segments", len(pack)))
 		buckets = append(buckets, pack)
 	}
 	remaining := t.squeezeSmallSegmentsToBuckets(toMerge.candidates, buckets, expectedSize)
@@ -581,6 +585,7 @@ func (t *compactionTrigger) generatePlans(segments []*SegmentInfo, signal *compa
 		if len(pack) == 0 {
 			break
 		}
+		reasons = append(reasons, fmt.Sprintf("packing %d small segments and non-planned segments", len(pack)))
 		buckets = append(buckets, pack)
 	}
 
@@ -595,7 +600,15 @@ func (t *compactionTrigger) generatePlans(segments []*SegmentInfo, signal *compa
 		pair := typeutil.NewPair(totalRows, segmentIDs)
 		tasks[i] = &pair
 	}
-	log.Info("generatePlans", zap.Int64("collectionID", signal.collectionID), zap.Int("plan_num", len(tasks)))
+
+	if len(tasks) > 0 {
+		log.Info("generated nontrivial compaction tasks",
+			zap.Int64("collectionID", signal.collectionID),
+			zap.Int("prioritizedCandidates", len(prioritizedCandidates)),
+			zap.Int("smallCandidates", len(smallCandidates)),
+			zap.Int("nonPlannedSegments", len(nonPlannedSegments)),
+			zap.Strings("reasons", reasons))
+	}
 	return tasks
 }
 

internal/datacoord/compaction_trigger_test.go

@@ -751,7 +751,8 @@ func Test_compactionTrigger_force_maxSegmentLimit(t *testing.T) {
 		},
 	}
 
-	for i := UniqueID(0); i < 50; i++ {
+	nSegments := 50
+	for i := UniqueID(0); i < UniqueID(nSegments); i++ {
 		info := &SegmentInfo{
 			SegmentInfo: &datapb.SegmentInfo{
 				ID:             i,
@@ -913,16 +914,13 @@ func Test_compactionTrigger_force_maxSegmentLimit(t *testing.T) {
 			assert.Equal(t, tt.wantErr, err != nil)
 			spy := (tt.fields.compactionHandler).(*spyCompactionHandler)
 
-			// should be split into two plans
-			plan := <-spy.spyChan
-			assert.NotEmpty(t, plan)
-
-			// TODO CZS
-			// assert.Equal(t, len(plan.SegmentBinlogs), 30)
-			plan = <-spy.spyChan
-			assert.NotEmpty(t, plan)
-			// TODO CZS
-			// assert.Equal(t, len(plan.SegmentBinlogs), 20)
+			select {
+			case plan := <-spy.spyChan:
+				assert.NotEmpty(t, plan)
+				assert.Equal(t, len(plan.SegmentBinlogs), nSegments)
+			case <-time.After(2 * time.Second):
+				assert.Fail(t, "timeout")
+			}
 		})
 	}
 }

internal/datacoord/knapsack.go

@@ -21,9 +21,6 @@ import (
 	"sort"
 
 	"github.com/bits-and-blooms/bitset"
-	"go.uber.org/zap"
-
-	"github.com/milvus-io/milvus/pkg/log"
 )
 
 type Sizable interface {
@@ -65,11 +62,6 @@ func (c *Knapsack[T]) tryPack(size, maxLeftSize, minSegs, maxSegs int64) (bitset
 
 	nSelections := selection.Count()
 	if left > maxLeftSize || nSelections < uint(minSegs) {
-		log.Debug("tryPack failed",
-			zap.String("name", c.name),
-			zap.Int64("left", left), zap.Int64("maxLeftSize", maxLeftSize),
-			zap.Int64("minSegs", minSegs),
-			zap.Uint("nselections", nSelections))
 		selection.ClearAll()
 		left = size
 	}

internal/datanode/compaction/mix_compactor.go

@@ -329,17 +329,23 @@ func (t *mixCompactionTask) Compact() (*datapb.CompactionPlanResult, error) {
 		return nil, errors.New("illegal compaction plan")
 	}
 
-	allSorted := true
-	for _, segment := range t.plan.GetSegmentBinlogs() {
-		if !segment.GetIsSorted() {
-			allSorted = false
-			break
+	sortMergeAppicable := paramtable.Get().DataNodeCfg.UseMergeSort.GetAsBool()
+	if sortMergeAppicable {
+		for _, segment := range t.plan.GetSegmentBinlogs() {
+			if !segment.GetIsSorted() {
+				sortMergeAppicable = false
+				break
+			}
+		}
+		if len(insertPaths) <= 1 || len(insertPaths) > paramtable.Get().DataNodeCfg.MaxSegmentMergeSort.GetAsInt() {
+			// sort merge is not applicable if there is only one segment or too many segments
+			sortMergeAppicable = false
 		}
 	}
 
 	var res []*datapb.CompactionSegment
-	if paramtable.Get().DataNodeCfg.UseMergeSort.GetAsBool() && allSorted && len(t.plan.GetSegmentBinlogs()) > 1 {
-		log.Info("all segments are sorted, use merge sort")
+	if sortMergeAppicable {
+		log.Info("compact by merge sort")
 		res, err = mergeSortMultipleSegments(ctxTimeout, t.plan, t.collectionID, t.partitionID, t.maxRows, t.binlogIO,
 			t.plan.GetSegmentBinlogs(), t.tr, t.currentTs, t.plan.GetCollectionTtl(), t.bm25FieldIDs)
 		if err != nil {

pkg/util/paramtable/component_param.go

@@ -3284,7 +3284,6 @@ type dataCoordConfig struct {
 	CompactionMaxParallelTasks       ParamItem `refreshable:"true"`
 	CompactionWorkerParalleTasks     ParamItem `refreshable:"true"`
 	MinSegmentToMerge                ParamItem `refreshable:"true"`
-	MaxSegmentToMerge                ParamItem `refreshable:"true"`
 	SegmentSmallProportion           ParamItem `refreshable:"true"`
 	SegmentCompactableProportion     ParamItem `refreshable:"true"`
 	SegmentExpansionRate             ParamItem `refreshable:"true"`
@@ -3610,13 +3609,6 @@ mix is prioritized by level: mix compactions first, then L0 compactions, then cl
 	}
 	p.MinSegmentToMerge.Init(base.mgr)
 
-	p.MaxSegmentToMerge = ParamItem{
-		Key:          "dataCoord.compaction.max.segment",
-		Version:      "2.0.0",
-		DefaultValue: "30",
-	}
-	p.MaxSegmentToMerge.Init(base.mgr)
-
 	p.SegmentSmallProportion = ParamItem{
 		Key:          "dataCoord.segment.smallProportion",
 		Version:      "2.0.0",
@@ -4303,6 +4295,7 @@ type dataNodeConfig struct {
 	L0BatchMemoryRatio       ParamItem `refreshable:"true"`
 	L0CompactionMaxBatchSize ParamItem `refreshable:"true"`
 	UseMergeSort             ParamItem `refreshable:"true"`
+	MaxSegmentMergeSort      ParamItem `refreshable:"true"`
 
 	GracefulStopTimeout ParamItem `refreshable:"true"`
 
@@ -4643,6 +4636,15 @@ if this parameter <= 0, will set it as 10`,
 	}
 	p.UseMergeSort.Init(base.mgr)
 
+	p.MaxSegmentMergeSort = ParamItem{
+		Key:          "dataNode.compaction.maxSegmentMergeSort",
+		Version:      "2.5.0",
+		Doc:          "The maximum number of segments to be merged in mergeSort mode.",
+		DefaultValue: "30",
+		Export:       true,
+	}
+	p.MaxSegmentMergeSort.Init(base.mgr)
+
 	p.GracefulStopTimeout = ParamItem{
 		Key:          "dataNode.gracefulStopTimeout",
 		Version:      "2.3.7",