// Licensed to the LF AI & Data foundation under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package datacoord contains core functions in datacoord
package datacoord

import (
	"context"
	"fmt"
	"path"
	"sync"
	"time"

	"github.com/golang/protobuf/proto"
	"github.com/samber/lo"
	"go.uber.org/zap"
	"golang.org/x/exp/maps"

	"github.com/milvus-io/milvus-proto/go-api/commonpb"
	"github.com/milvus-io/milvus-proto/go-api/schemapb"
	"github.com/milvus-io/milvus/internal/common"
	"github.com/milvus-io/milvus/internal/log"
	"github.com/milvus-io/milvus/internal/metastore"
	"github.com/milvus-io/milvus/internal/metastore/model"
	"github.com/milvus-io/milvus/internal/metrics"
	"github.com/milvus-io/milvus/internal/proto/datapb"
	"github.com/milvus-io/milvus/internal/proto/internalpb"
	"github.com/milvus-io/milvus/internal/storage"
	"github.com/milvus-io/milvus/internal/util/metautil"
	"github.com/milvus-io/milvus/internal/util/timerecord"
	"github.com/milvus-io/milvus/internal/util/tsoutil"
	"github.com/milvus-io/milvus/internal/util/typeutil"
)

type meta struct {
	sync.RWMutex
	ctx          context.Context
	catalog      metastore.DataCoordCatalog
	collections  map[UniqueID]*collectionInfo       // collection id to collection info
	segments     *SegmentsInfo                      // segment id to segment info
	channelCPs   map[string]*internalpb.MsgPosition // vChannel -> channel checkpoint/see position
	chunkManager storage.ChunkManager

	// collectionIndexes records which indexes are on the collection
	// collID -> indexID -> index
	indexes map[UniqueID]map[UniqueID]*model.Index
	// buildID2Meta records the meta information of the segment
	// buildID -> segmentIndex
	buildID2SegmentIndex map[UniqueID]*model.SegmentIndex
}

// A local cache of segment metric update. Must call commit() to take effect.
type segMetricMutation struct {
	stateChange       map[string]int // segment state -> state change count (to increase or decrease).
	rowCountChange    int64          // Change in # of rows.
	rowCountAccChange int64          // Total # of historical added rows, accumulated.
}

type collectionInfo struct {
	ID             int64
	Schema         *schemapb.CollectionSchema
	Partitions     []int64
	StartPositions []*commonpb.KeyDataPair
	Properties     map[string]string
}

// NewMeta creates meta from provided `kv.TxnKV`
func newMeta(ctx context.Context, catalog metastore.DataCoordCatalog, chunkManager storage.ChunkManager) (*meta, error) {
	mt := &meta{
		ctx:                  ctx,
		catalog:              catalog,
		collections:          make(map[UniqueID]*collectionInfo),
		segments:             NewSegmentsInfo(),
		channelCPs:           make(map[string]*internalpb.MsgPosition),
		chunkManager:         chunkManager,
		indexes:              make(map[UniqueID]map[UniqueID]*model.Index),
		buildID2SegmentIndex: make(map[UniqueID]*model.SegmentIndex),
	}
	err := mt.reloadFromKV()
	if err != nil {
		return nil, err
	}
	return mt, nil
}

// reloadFromKV loads meta from KV storage
func (m *meta) reloadFromKV() error {
	record := timerecord.NewTimeRecorder("datacoord")
	segments, err := m.catalog.ListSegments(m.ctx)
	if err != nil {
		return err
	}
	metrics.DataCoordNumCollections.WithLabelValues().Set(0)
	metrics.DataCoordNumSegments.WithLabelValues(metrics.SealedSegmentLabel).Set(0)
	metrics.DataCoordNumSegments.WithLabelValues(metrics.GrowingSegmentLabel).Set(0)
	metrics.DataCoordNumSegments.WithLabelValues(metrics.FlushedSegmentLabel).Set(0)
	metrics.DataCoordNumSegments.WithLabelValues(metrics.FlushingSegmentLabel).Set(0)
	metrics.DataCoordNumSegments.WithLabelValues(metrics.DroppedSegmentLabel).Set(0)
	metrics.DataCoordNumStoredRows.WithLabelValues().Set(0)
	numStoredRows := int64(0)
	for _, segment := range segments {
		m.segments.SetSegment(segment.ID, NewSegmentInfo(segment))
		metrics.DataCoordNumSegments.WithLabelValues(segment.State.String()).Inc()
		if segment.State == commonpb.SegmentState_Flushed {
			numStoredRows += segment.NumOfRows
		}
	}
	metrics.DataCoordNumStoredRows.WithLabelValues().Set(float64(numStoredRows))
	metrics.DataCoordNumStoredRowsCounter.WithLabelValues().Add(float64(numStoredRows))

	channelCPs, err := m.catalog.ListChannelCheckpoint(m.ctx)
	if err != nil {
		return err
	}
	for vChannel, pos := range channelCPs {
		m.channelCPs[vChannel] = pos
	}

	// load field indexes
	fieldIndexes, err := m.catalog.ListIndexes(m.ctx)
	if err != nil {
		log.Error("DataCoord meta reloadFromKV load field indexes fail", zap.Error(err))
		return err
	}
	for _, fieldIndex := range fieldIndexes {
		m.updateCollectionIndex(fieldIndex)
	}
	segmentIndexes, err := m.catalog.ListSegmentIndexes(m.ctx)
	if err != nil {
		log.Error("DataCoord meta reloadFromKV load segment indexes fail", zap.Error(err))
		return err
	}
	for _, segIdx := range segmentIndexes {
		m.updateSegmentIndex(segIdx)
	}

	record.Record("meta reloadFromKV")
	return nil
}

// AddCollection adds a collection into meta
// Note that collection info is just for caching and will not be set into etcd from datacoord
func (m *meta) AddCollection(collection *collectionInfo) {
	log.Info("meta update: add collection",
		zap.Int64("collection ID", collection.ID))
	m.Lock()
	defer m.Unlock()
	m.collections[collection.ID] = collection
	metrics.DataCoordNumCollections.WithLabelValues().Set(float64(len(m.collections)))
	log.Info("meta update: add collection - complete",
		zap.Int64("collection ID", collection.ID))
}

// GetCollection returns collection info with provided collection id from local cache
func (m *meta) GetCollection(collectionID UniqueID) *collectionInfo {
	m.RLock()
	defer m.RUnlock()
	collection, ok := m.collections[collectionID]
	if !ok {
		return nil
	}
	return collection
}

func (m *meta) GetClonedCollectionInfo(collectionID UniqueID) *collectionInfo {
	m.RLock()
	defer m.RUnlock()

	coll, ok := m.collections[collectionID]
	if !ok {
		return nil
	}

	clonedProperties := make(map[string]string)
	maps.Copy(clonedProperties, coll.Properties)
	cloneColl := &collectionInfo{
		ID:             coll.ID,
		Schema:         proto.Clone(coll.Schema).(*schemapb.CollectionSchema),
		Partitions:     coll.Partitions,
		StartPositions: common.CloneKeyDataPairs(coll.StartPositions),
		Properties:     clonedProperties,
	}

	return cloneColl
}

// chanPartSegments is an internal result struct, which is aggregates of SegmentInfos with same collectionID, partitionID and channelName
type chanPartSegments struct {
	collectionID UniqueID
	partitionID  UniqueID
	channelName  string
	segments     []*SegmentInfo
}

// GetSegmentsChanPart returns segments organized in Channel-Partition dimension with selector applied
func (m *meta) GetSegmentsChanPart(selector SegmentInfoSelector) []*chanPartSegments {
	m.RLock()
	defer m.RUnlock()
	mDimEntry := make(map[string]*chanPartSegments)

	for _, segmentInfo := range m.segments.segments {
		if !selector(segmentInfo) {
			continue
		}
		dim := fmt.Sprintf("%d-%s", segmentInfo.PartitionID, segmentInfo.InsertChannel)
		entry, ok := mDimEntry[dim]
		if !ok {
			entry = &chanPartSegments{
				collectionID: segmentInfo.CollectionID,
				partitionID:  segmentInfo.PartitionID,
				channelName:  segmentInfo.InsertChannel,
			}
			mDimEntry[dim] = entry
		}
		entry.segments = append(entry.segments, segmentInfo)
	}

	result := make([]*chanPartSegments, 0, len(mDimEntry))
	for _, entry := range mDimEntry {
		result = append(result, entry)
	}
	return result
}

// GetNumRowsOfCollection returns total rows count of segments belongs to provided collection
func (m *meta) GetNumRowsOfCollection(collectionID UniqueID) int64 {
	m.RLock()
	defer m.RUnlock()
	var ret int64
	segments := m.segments.GetSegments()
	for _, segment := range segments {
		if isSegmentHealthy(segment) && segment.GetCollectionID() == collectionID {
			ret += segment.GetNumOfRows()
		}
	}
	return ret
}

// GetTotalBinlogSize returns the total size (bytes) of healthy segments in cluster.
func (m *meta) GetTotalBinlogSize() int64 {
	m.RLock()
	defer m.RUnlock()
	var totalHealthySize int64
	segments := m.segments.GetSegments()
	sizes := make(map[commonpb.SegmentState]int64)
	for _, segment := range segments {
		if isSegmentHealthy(segment) {
			totalHealthySize += segment.getSegmentSize()
		}
		sizes[segment.GetState()] += segment.getSegmentSize()
	}
	for state, size := range sizes {
		metrics.DataCoordStoredBinlogSize.WithLabelValues(state.String()).Set(float64(size))
	}
	return totalHealthySize
}

// AddSegment records segment info, persisting info into kv store
func (m *meta) AddSegment(segment *SegmentInfo) error {
	log.Info("meta update: adding segment",
		zap.Int64("segment ID", segment.GetID()))
	m.Lock()
	defer m.Unlock()
	if err := m.catalog.AddSegment(m.ctx, segment.SegmentInfo); err != nil {
		log.Error("meta update: adding segment failed",
			zap.Int64("segment ID", segment.GetID()),
			zap.Error(err))
		return err
	}
	m.segments.SetSegment(segment.GetID(), segment)
	metrics.DataCoordNumSegments.WithLabelValues(segment.GetState().String()).Inc()
	log.Info("meta update: adding segment - complete",
		zap.Int64("segment ID", segment.GetID()))
	return nil
}

// DropSegment remove segment with provided id, etcd persistence also removed
func (m *meta) DropSegment(segmentID UniqueID) error {
	log.Info("meta update: dropping segment",
		zap.Int64("segment ID", segmentID))
	m.Lock()
	defer m.Unlock()
	segment := m.segments.GetSegment(segmentID)
	if segment == nil {
		log.Warn("meta update: dropping segment failed - segment not found",
			zap.Int64("segment ID", segmentID))
		return nil
	}
	if err := m.catalog.DropSegment(m.ctx, segment.SegmentInfo); err != nil {
		log.Warn("meta update: dropping segment failed",
			zap.Int64("segment ID", segmentID),
			zap.Error(err))
		return err
	}
	metrics.DataCoordNumSegments.WithLabelValues(segment.GetState().String()).Dec()
	m.segments.DropSegment(segmentID)
	log.Info("meta update: dropping segment - complete",
		zap.Int64("segment ID", segmentID))
	return nil
}

// GetSegment returns segment info with provided id
// if not segment is found, nil will be returned
func (m *meta) GetSegment(segID UniqueID) *SegmentInfo {
	m.RLock()
	defer m.RUnlock()
	segment := m.segments.GetSegment(segID)
	if segment != nil && isSegmentHealthy(segment) {
		return segment
	}
	return nil
}

// GetSegmentUnsafe returns segment info with provided id
// include the unhealthy segment
// if not segment is found, nil will be returned
func (m *meta) GetSegmentUnsafe(segID UniqueID) *SegmentInfo {
	m.RLock()
	defer m.RUnlock()
	return m.segments.GetSegment(segID)
}

// GetAllSegmentsUnsafe returns all segments
func (m *meta) GetAllSegmentsUnsafe() []*SegmentInfo {
	m.RLock()
	defer m.RUnlock()
	return m.segments.GetSegments()
}

// SetState setting segment with provided ID state
func (m *meta) SetState(segmentID UniqueID, targetState commonpb.SegmentState) error {
	log.Info("meta update: setting segment state",
		zap.Int64("segment ID", segmentID),
		zap.Any("target state", targetState))
	m.Lock()
	defer m.Unlock()
	curSegInfo := m.segments.GetSegment(segmentID)
	if curSegInfo == nil {
		log.Warn("meta update: setting segment state - segment not found",
			zap.Int64("segment ID", segmentID),
			zap.Any("target state", targetState))
		// idempotent drop
		if targetState == commonpb.SegmentState_Dropped {
			return nil
		}
		return fmt.Errorf("segment is not exist with ID = %d", segmentID)
	}
	// Persist segment updates first.
	clonedSegment := curSegInfo.Clone()
	metricMutation := &segMetricMutation{
		stateChange: make(map[string]int),
	}
	// Update segment state and prepare segment metric update.
	updateSegStateAndPrepareMetrics(clonedSegment, targetState, metricMutation)
	if clonedSegment != nil && isSegmentHealthy(clonedSegment) {
		if err := m.catalog.AlterSegment(m.ctx, clonedSegment.SegmentInfo, curSegInfo.SegmentInfo); err != nil {
			log.Error("meta update: setting segment state - failed to alter segments",
				zap.Int64("segment ID", segmentID),
				zap.String("target state", targetState.String()),
				zap.Error(err))
			return err
		}
		// Apply segment metric update after successful meta update.
		metricMutation.commit()
	}
	// Update in-memory meta.
	m.segments.SetState(segmentID, targetState)
	log.Info("meta update: setting segment state - complete",
		zap.Int64("segment ID", segmentID),
		zap.String("target state", targetState.String()))
	return nil
}

// UnsetIsImporting removes the `isImporting` flag of a segment.
func (m *meta) UnsetIsImporting(segmentID UniqueID) error {
	log.Info("meta update: unsetting isImport state of segment",
		zap.Int64("segment ID", segmentID))
	m.Lock()
	defer m.Unlock()
	curSegInfo := m.segments.GetSegment(segmentID)
	if curSegInfo == nil {
		return fmt.Errorf("segment not found %d", segmentID)
	}
	// Persist segment updates first.
	clonedSegment := curSegInfo.Clone()
	clonedSegment.IsImporting = false
	if isSegmentHealthy(clonedSegment) {
		if err := m.catalog.AlterSegment(m.ctx, clonedSegment.SegmentInfo, curSegInfo.SegmentInfo); err != nil {
			log.Error("meta update: unsetting isImport state of segment - failed to unset segment isImporting state",
				zap.Int64("segment ID", segmentID),
				zap.Error(err))
			return err
		}
	}
	// Update in-memory meta.
	m.segments.SetIsImporting(segmentID, false)
	log.Info("meta update: unsetting isImport state of segment - complete",
		zap.Int64("segment ID", segmentID))
	return nil
}

// UpdateFlushSegmentsInfo update segment partial/completed flush info
// `flushed` parameter indicating whether segment is flushed completely or partially
// `binlogs`, `checkpoints` and `statPositions` are persistence data for segment
func (m *meta) UpdateFlushSegmentsInfo(
	segmentID UniqueID,
	flushed bool,
	dropped bool,
	importing bool,
	binlogs, statslogs, deltalogs []*datapb.FieldBinlog,
	checkpoints []*datapb.CheckPoint,
	startPositions []*datapb.SegmentStartPosition,
) error {
	log.Info("meta update: update flush segments info",
		zap.Int64("segmentId", segmentID),
		zap.Int("binlog", len(binlogs)),
		zap.Int("stats log", len(statslogs)),
		zap.Int("delta logs", len(deltalogs)),
		zap.Bool("flushed", flushed),
		zap.Bool("dropped", dropped),
		zap.Any("check points", checkpoints),
		zap.Any("start position", startPositions),
		zap.Bool("importing", importing))
	m.Lock()
	defer m.Unlock()

	segment := m.segments.GetSegment(segmentID)
	if importing {
		m.segments.SetRowCount(segmentID, segment.currRows)
		segment = m.segments.GetSegment(segmentID)
	}
	if segment == nil || !isSegmentHealthy(segment) {
		log.Warn("meta update: update flush segments info - segment not found",
			zap.Int64("segment ID", segmentID),
			zap.Bool("segment nil", segment == nil),
			zap.Bool("segment unhealthy", !isSegmentHealthy(segment)))
		return nil
	}

	metricMutation := &segMetricMutation{
		stateChange: make(map[string]int),
	}
	clonedSegment := segment.Clone()
	modSegments := make(map[UniqueID]*SegmentInfo)
	if flushed {
		// Update segment state and prepare metrics.
		updateSegStateAndPrepareMetrics(clonedSegment, commonpb.SegmentState_Flushing, metricMutation)
		modSegments[segmentID] = clonedSegment
	}
	if dropped {
		// Update segment state and prepare metrics.
		updateSegStateAndPrepareMetrics(clonedSegment, commonpb.SegmentState_Dropped, metricMutation)
		clonedSegment.DroppedAt = uint64(time.Now().UnixNano())
		modSegments[segmentID] = clonedSegment
	}
	// TODO add diff encoding and compression
	currBinlogs := clonedSegment.GetBinlogs()
	var getFieldBinlogs = func(id UniqueID, binlogs []*datapb.FieldBinlog) *datapb.FieldBinlog {
		for _, binlog := range binlogs {
			if id == binlog.GetFieldID() {
				return binlog
			}
		}
		return nil
	}
	// binlogs
	for _, tBinlogs := range binlogs {
		fieldBinlogs := getFieldBinlogs(tBinlogs.GetFieldID(), currBinlogs)
		if fieldBinlogs == nil {
			currBinlogs = append(currBinlogs, tBinlogs)
		} else {
			fieldBinlogs.Binlogs = append(fieldBinlogs.Binlogs, tBinlogs.Binlogs...)
		}
	}
	clonedSegment.Binlogs = currBinlogs
	// statlogs
	currStatsLogs := clonedSegment.GetStatslogs()
	for _, tStatsLogs := range statslogs {
		fieldStatsLog := getFieldBinlogs(tStatsLogs.GetFieldID(), currStatsLogs)
		if fieldStatsLog == nil {
			currStatsLogs = append(currStatsLogs, tStatsLogs)
		} else {
			fieldStatsLog.Binlogs = append(fieldStatsLog.Binlogs, tStatsLogs.Binlogs...)
		}
	}
	clonedSegment.Statslogs = currStatsLogs
	// deltalogs
	currDeltaLogs := clonedSegment.GetDeltalogs()
	for _, tDeltaLogs := range deltalogs {
		fieldDeltaLogs := getFieldBinlogs(tDeltaLogs.GetFieldID(), currDeltaLogs)
		if fieldDeltaLogs == nil {
			currDeltaLogs = append(currDeltaLogs, tDeltaLogs)
		} else {
			fieldDeltaLogs.Binlogs = append(fieldDeltaLogs.Binlogs, tDeltaLogs.Binlogs...)
		}
	}
	clonedSegment.Deltalogs = currDeltaLogs
	modSegments[segmentID] = clonedSegment
	var getClonedSegment = func(segmentID UniqueID) *SegmentInfo {
		if s, ok := modSegments[segmentID]; ok {
			return s
		}
		if s := m.segments.GetSegment(segmentID); s != nil && isSegmentHealthy(s) {
			return s.Clone()
		}
		return nil
	}
	for _, pos := range startPositions {
		if len(pos.GetStartPosition().GetMsgID()) == 0 {
			continue
		}
		s := getClonedSegment(pos.GetSegmentID())
		if s == nil {
			continue
		}

		s.StartPosition = pos.GetStartPosition()
		modSegments[pos.GetSegmentID()] = s
	}
	for _, cp := range checkpoints {
		s := getClonedSegment(cp.GetSegmentID())
		if s == nil {
			continue
		}

		if s.DmlPosition != nil && s.DmlPosition.Timestamp >= cp.Position.Timestamp {
			// segment position in etcd is larger than checkpoint, then dont change it
			continue
		}

		s.DmlPosition = cp.GetPosition()
		s.NumOfRows = cp.GetNumOfRows()
		modSegments[cp.GetSegmentID()] = s
	}
	segments := make([]*datapb.SegmentInfo, 0, len(modSegments))
	for _, seg := range modSegments {
		segments = append(segments, seg.SegmentInfo)
	}
	if err := m.catalog.AlterSegments(m.ctx, segments); err != nil {
		log.Error("meta update: update flush segments info - failed to store flush segment info into Etcd",
			zap.Error(err))
		return err
	}
	// Apply metric mutation after a successful meta update.
	metricMutation.commit()
	// update memory status
	for id, s := range modSegments {
		m.segments.SetSegment(id, s)
	}
	log.Info("meta update: update flush segments info - update flush segments info successfully",
		zap.Int64("segment ID", segmentID))
	return nil
}

// UpdateDropChannelSegmentInfo updates segment checkpoints and binlogs before drop
// reusing segment info to pass segment id, binlogs, statslog, deltalog, start position and checkpoint
func (m *meta) UpdateDropChannelSegmentInfo(channel string, segments []*SegmentInfo) error {
	log.Info("meta update: update drop channel segment info",
		zap.String("channel", channel))
	m.Lock()
	defer m.Unlock()

	// Prepare segment metric mutation.
	metricMutation := &segMetricMutation{
		stateChange: make(map[string]int),
	}
	modSegments := make(map[UniqueID]*SegmentInfo)
	// save new segments flushed from buffer data
	for _, seg2Drop := range segments {
		var segment *SegmentInfo
		segment, metricMutation = m.mergeDropSegment(seg2Drop)
		if segment != nil {
			modSegments[seg2Drop.GetID()] = segment
		}
	}
	// set existed segments of channel to Dropped
	for _, seg := range m.segments.segments {
		if seg.InsertChannel != channel {
			continue
		}
		_, ok := modSegments[seg.ID]
		// seg inf mod segments are all in dropped state
		if !ok {
			clonedSeg := seg.Clone()
			updateSegStateAndPrepareMetrics(clonedSeg, commonpb.SegmentState_Dropped, metricMutation)
			modSegments[seg.ID] = clonedSeg
		}
	}
	err := m.batchSaveDropSegments(channel, modSegments)
	if err != nil {
		log.Error("meta update: update drop channel segment info failed",
			zap.String("channel", channel),
			zap.Error(err))
	} else {
		log.Info("meta update: update drop channel segment info - complete",
			zap.String("channel", channel))
		// Apply segment metric mutation on successful meta update.
		metricMutation.commit()
	}
	return err
}

// mergeDropSegment merges drop segment information with meta segments
func (m *meta) mergeDropSegment(seg2Drop *SegmentInfo) (*SegmentInfo, *segMetricMutation) {
	metricMutation := &segMetricMutation{
		stateChange: make(map[string]int),
	}

	segment := m.segments.GetSegment(seg2Drop.ID)
	// healthy check makes sure the Idempotence
	if segment == nil || !isSegmentHealthy(segment) {
		log.Warn("UpdateDropChannel skipping nil or unhealthy", zap.Bool("is nil", segment == nil),
			zap.Bool("isHealthy", isSegmentHealthy(segment)))
		return nil, metricMutation
	}

	clonedSegment := segment.Clone()
	updateSegStateAndPrepareMetrics(clonedSegment, commonpb.SegmentState_Dropped, metricMutation)

	currBinlogs := clonedSegment.GetBinlogs()

	var getFieldBinlogs = func(id UniqueID, binlogs []*datapb.FieldBinlog) *datapb.FieldBinlog {
		for _, binlog := range binlogs {
			if id == binlog.GetFieldID() {
				return binlog
			}
		}
		return nil
	}
	// binlogs
	for _, tBinlogs := range seg2Drop.GetBinlogs() {
		fieldBinlogs := getFieldBinlogs(tBinlogs.GetFieldID(), currBinlogs)
		if fieldBinlogs == nil {
			currBinlogs = append(currBinlogs, tBinlogs)
		} else {
			fieldBinlogs.Binlogs = append(fieldBinlogs.Binlogs, tBinlogs.Binlogs...)
		}
	}
	clonedSegment.Binlogs = currBinlogs
	// statlogs
	currStatsLogs := clonedSegment.GetStatslogs()
	for _, tStatsLogs := range seg2Drop.GetStatslogs() {
		fieldStatsLog := getFieldBinlogs(tStatsLogs.GetFieldID(), currStatsLogs)
		if fieldStatsLog == nil {
			currStatsLogs = append(currStatsLogs, tStatsLogs)
		} else {
			fieldStatsLog.Binlogs = append(fieldStatsLog.Binlogs, tStatsLogs.Binlogs...)
		}
	}
	clonedSegment.Statslogs = currStatsLogs
	// deltalogs
	clonedSegment.Deltalogs = append(clonedSegment.Deltalogs, seg2Drop.GetDeltalogs()...)

	// start position
	if seg2Drop.GetStartPosition() != nil {
		clonedSegment.StartPosition = seg2Drop.GetStartPosition()
	}
	// checkpoint
	if seg2Drop.GetDmlPosition() != nil {
		clonedSegment.DmlPosition = seg2Drop.GetDmlPosition()
	}
	clonedSegment.currRows = seg2Drop.currRows
	clonedSegment.NumOfRows = seg2Drop.currRows
	return clonedSegment, metricMutation
}

// batchSaveDropSegments saves drop segments info with channel removal flag
// since the channel unwatching operation is not atomic here
// ** the removal flag is always with last batch
// ** the last batch must contains at least one segment
//  1. when failure occurs between batches, failover mechanism will continue with the earlist  checkpoint of this channel
//     since the flag is not marked so DataNode can re-consume the drop collection msg
//  2. when failure occurs between save meta and unwatch channel, the removal flag shall be check before let datanode watch this channel
func (m *meta) batchSaveDropSegments(channel string, modSegments map[int64]*SegmentInfo) error {
	var modSegIDs []int64
	for k := range modSegments {
		modSegIDs = append(modSegIDs, k)
	}
	log.Info("meta update: batch save drop segments",
		zap.Int64s("drop segments", modSegIDs))
	segments := make([]*datapb.SegmentInfo, 0)
	for _, seg := range modSegments {
		segments = append(segments, seg.SegmentInfo)
	}
	err := m.catalog.SaveDroppedSegmentsInBatch(m.ctx, segments)
	if err != nil {
		return err
	}

	if err = m.catalog.MarkChannelDeleted(m.ctx, channel); err != nil {
		return err
	}

	// update memory info
	for id, segment := range modSegments {
		m.segments.SetSegment(id, segment)
	}

	return nil
}

// GetSegmentsByChannel returns all segment info which insert channel equals provided `dmlCh`
func (m *meta) GetSegmentsByChannel(dmlCh string) []*SegmentInfo {
	m.RLock()
	defer m.RUnlock()
	infos := make([]*SegmentInfo, 0)
	segments := m.segments.GetSegments()
	for _, segment := range segments {
		if !isSegmentHealthy(segment) || segment.InsertChannel != dmlCh {
			continue
		}
		infos = append(infos, segment)
	}
	return infos
}

// GetSegmentsOfCollection get all segments of collection
func (m *meta) GetSegmentsOfCollection(collectionID UniqueID) []*SegmentInfo {
	m.RLock()
	defer m.RUnlock()

	ret := make([]*SegmentInfo, 0)
	segments := m.segments.GetSegments()
	for _, segment := range segments {
		if isSegmentHealthy(segment) && segment.GetCollectionID() == collectionID {
			ret = append(ret, segment)
		}
	}
	return ret
}

// GetSegmentsIDOfCollection returns all segment ids which collection equals to provided `collectionID`
func (m *meta) GetSegmentsIDOfCollection(collectionID UniqueID) []UniqueID {
	m.RLock()
	defer m.RUnlock()
	ret := make([]UniqueID, 0)
	segments := m.segments.GetSegments()
	for _, segment := range segments {
		if isSegmentHealthy(segment) && segment.CollectionID == collectionID {
			ret = append(ret, segment.ID)
		}
	}
	return ret
}

// GetSegmentsIDOfCollection returns all segment ids which collection equals to provided `collectionID`
func (m *meta) GetSegmentsIDOfCollectionWithDropped(collectionID UniqueID) []UniqueID {
	m.RLock()
	defer m.RUnlock()
	ret := make([]UniqueID, 0)
	segments := m.segments.GetSegments()
	for _, segment := range segments {
		if segment != nil &&
			segment.GetState() != commonpb.SegmentState_SegmentStateNone &&
			segment.GetState() != commonpb.SegmentState_NotExist &&
			segment.CollectionID == collectionID {
			ret = append(ret, segment.ID)
		}
	}
	return ret
}

// GetSegmentsIDOfPartition returns all segments ids which collection & partition equals to provided `collectionID`, `partitionID`
func (m *meta) GetSegmentsIDOfPartition(collectionID, partitionID UniqueID) []UniqueID {
	m.RLock()
	defer m.RUnlock()
	ret := make([]UniqueID, 0)
	segments := m.segments.GetSegments()
	for _, segment := range segments {
		if isSegmentHealthy(segment) && segment.CollectionID == collectionID && segment.PartitionID == partitionID {
			ret = append(ret, segment.ID)
		}
	}
	return ret
}

// GetSegmentsIDOfPartition returns all segments ids which collection & partition equals to provided `collectionID`, `partitionID`
func (m *meta) GetSegmentsIDOfPartitionWithDropped(collectionID, partitionID UniqueID) []UniqueID {
	m.RLock()
	defer m.RUnlock()
	ret := make([]UniqueID, 0)
	segments := m.segments.GetSegments()
	for _, segment := range segments {
		if segment != nil &&
			segment.GetState() != commonpb.SegmentState_SegmentStateNone &&
			segment.GetState() != commonpb.SegmentState_NotExist &&
			segment.CollectionID == collectionID &&
			segment.PartitionID == partitionID {
			ret = append(ret, segment.ID)
		}
	}
	return ret
}

// GetNumRowsOfPartition returns row count of segments belongs to provided collection & partition
func (m *meta) GetNumRowsOfPartition(collectionID UniqueID, partitionID UniqueID) int64 {
	m.RLock()
	defer m.RUnlock()
	var ret int64
	segments := m.segments.GetSegments()
	for _, segment := range segments {
		if isSegmentHealthy(segment) && segment.CollectionID == collectionID && segment.PartitionID == partitionID {
			ret += segment.NumOfRows
		}
	}
	return ret
}

// GetUnFlushedSegments get all segments which state is not `Flushing` nor `Flushed`
func (m *meta) GetUnFlushedSegments() []*SegmentInfo {
	m.RLock()
	defer m.RUnlock()
	ret := make([]*SegmentInfo, 0)
	segments := m.segments.GetSegments()
	for _, segment := range segments {
		if segment.State == commonpb.SegmentState_Growing || segment.State == commonpb.SegmentState_Sealed {
			ret = append(ret, segment)
		}
	}
	return ret
}

// GetFlushingSegments get all segments which state is `Flushing`
func (m *meta) GetFlushingSegments() []*SegmentInfo {
	m.RLock()
	defer m.RUnlock()
	ret := make([]*SegmentInfo, 0)
	segments := m.segments.GetSegments()
	for _, info := range segments {
		if info.State == commonpb.SegmentState_Flushing {
			ret = append(ret, info)
		}
	}
	return ret
}

// SelectSegments select segments with selector
func (m *meta) SelectSegments(selector SegmentInfoSelector) []*SegmentInfo {
	m.RLock()
	defer m.RUnlock()
	var ret []*SegmentInfo
	segments := m.segments.GetSegments()
	for _, info := range segments {
		if selector(info) {
			ret = append(ret, info)
		}
	}
	return ret
}

// AddAllocation add allocation in segment
func (m *meta) AddAllocation(segmentID UniqueID, allocation *Allocation) error {
	log.Info("meta update: add allocation",
		zap.Int64("segmentID", segmentID),
		zap.Any("allocation", allocation))
	m.Lock()
	defer m.Unlock()
	curSegInfo := m.segments.GetSegment(segmentID)
	if curSegInfo == nil {
		// TODO: Error handling.
		log.Warn("meta update: add allocation failed - segment not found",
			zap.Int64("segmentID", segmentID))
		return nil
	}
	// Persist segment updates first.
	clonedSegment := curSegInfo.Clone(AddAllocation(allocation))
	if clonedSegment != nil && isSegmentHealthy(clonedSegment) {
		if err := m.catalog.AlterSegment(m.ctx, clonedSegment.SegmentInfo, curSegInfo.SegmentInfo); err != nil {
			log.Error("meta update: add allocation failed",
				zap.Int64("segment ID", segmentID),
				zap.Error(err))
			return err
		}
	}
	// Update in-memory meta.
	m.segments.AddAllocation(segmentID, allocation)
	log.Info("meta update: add allocation - complete",
		zap.Int64("segmentID", segmentID))
	return nil
}

// SetAllocations set Segment allocations, will overwrite ALL original allocations
// Note that allocations is not persisted in KV store
func (m *meta) SetAllocations(segmentID UniqueID, allocations []*Allocation) {
	m.Lock()
	defer m.Unlock()
	m.segments.SetAllocations(segmentID, allocations)
}

// SetCurrentRows set current row count for segment with provided `segmentID`
// Note that currRows is not persisted in KV store
func (m *meta) SetCurrentRows(segmentID UniqueID, rows int64) {
	m.Lock()
	defer m.Unlock()
	m.segments.SetCurrentRows(segmentID, rows)
}

// SetLastFlushTime set LastFlushTime for segment with provided `segmentID`
// Note that lastFlushTime is not persisted in KV store
func (m *meta) SetLastFlushTime(segmentID UniqueID, t time.Time) {
	m.Lock()
	defer m.Unlock()
	m.segments.SetFlushTime(segmentID, t)
}

// SetSegmentCompacting sets compaction state for segment
func (m *meta) SetSegmentCompacting(segmentID UniqueID, compacting bool) {
	m.Lock()
	defer m.Unlock()

	m.segments.SetIsCompacting(segmentID, compacting)
}

// PrepareCompleteCompactionMutation returns
// - the segment info of compactedFrom segments before compaction to revert
// - the segment info of compactedFrom segments after compaction to alter
// - the segment info of compactedTo segment after compaction to add
// The compactedTo segment could contain 0 numRows
func (m *meta) PrepareCompleteCompactionMutation(compactionLogs []*datapb.CompactionSegmentBinlogs,
	result *datapb.CompactionResult) ([]*SegmentInfo, []*SegmentInfo, *SegmentInfo, *segMetricMutation, error) {
	log.Info("meta update: prepare for complete compaction mutation")
	m.Lock()
	defer m.Unlock()

	var (
		oldSegments = make([]*SegmentInfo, 0, len(compactionLogs))
		modSegments = make([]*SegmentInfo, 0, len(compactionLogs))
	)

	metricMutation := &segMetricMutation{
		stateChange: make(map[string]int),
	}
	for _, cl := range compactionLogs {
		if segment := m.segments.GetSegment(cl.GetSegmentID()); segment != nil {
			oldSegments = append(oldSegments, segment.Clone())

			cloned := segment.Clone()
			updateSegStateAndPrepareMetrics(cloned, commonpb.SegmentState_Dropped, metricMutation)
			cloned.DroppedAt = uint64(time.Now().UnixNano())
			modSegments = append(modSegments, cloned)
		}
	}

	var startPosition, dmlPosition *internalpb.MsgPosition
	for _, s := range modSegments {
		if dmlPosition == nil ||
			s.GetDmlPosition() != nil && s.GetDmlPosition().GetTimestamp() < dmlPosition.GetTimestamp() {
			dmlPosition = s.GetDmlPosition()
		}

		if startPosition == nil ||
			s.GetStartPosition() != nil && s.GetStartPosition().GetTimestamp() < startPosition.GetTimestamp() {
			startPosition = s.GetStartPosition()
		}
	}

	// find new added delta logs when executing compaction
	var originDeltalogs []*datapb.FieldBinlog
	for _, s := range modSegments {
		originDeltalogs = append(originDeltalogs, s.GetDeltalogs()...)
	}

	var deletedDeltalogs []*datapb.FieldBinlog
	for _, l := range compactionLogs {
		deletedDeltalogs = append(deletedDeltalogs, l.GetDeltalogs()...)
	}

	newAddedDeltalogs := m.updateDeltalogs(originDeltalogs, deletedDeltalogs, nil)
	copiedDeltalogs, err := m.copyDeltaFiles(newAddedDeltalogs, modSegments[0].CollectionID, modSegments[0].PartitionID, result.GetSegmentID())
	if err != nil {
		return nil, nil, nil, nil, err
	}
	deltalogs := append(result.GetDeltalogs(), copiedDeltalogs...)

	compactionFrom := make([]UniqueID, 0, len(modSegments))
	for _, s := range modSegments {
		compactionFrom = append(compactionFrom, s.GetID())
	}

	segmentInfo := &datapb.SegmentInfo{
		ID:                  result.GetSegmentID(),
		CollectionID:        modSegments[0].CollectionID,
		PartitionID:         modSegments[0].PartitionID,
		InsertChannel:       modSegments[0].InsertChannel,
		NumOfRows:           result.NumOfRows,
		State:               commonpb.SegmentState_Flushing,
		MaxRowNum:           modSegments[0].MaxRowNum,
		Binlogs:             result.GetInsertLogs(),
		Statslogs:           result.GetField2StatslogPaths(),
		Deltalogs:           deltalogs,
		StartPosition:       startPosition,
		DmlPosition:         dmlPosition,
		CreatedByCompaction: true,
		CompactionFrom:      compactionFrom,
	}
	segment := NewSegmentInfo(segmentInfo)
	metricMutation.addNewSeg(segment.GetState(), segment.GetNumOfRows())
	log.Info("meta update: prepare for complete compaction mutation - complete",
		zap.Int64("collection ID", segment.GetCollectionID()),
		zap.Int64("partition ID", segment.GetPartitionID()),
		zap.Int64("new segment ID", segment.GetID()),
		zap.Int64("new segment num of rows", segment.GetNumOfRows()),
		zap.Any("compacted from", segment.GetCompactionFrom()))

	return oldSegments, modSegments, segment, metricMutation, nil
}

func (m *meta) copyDeltaFiles(binlogs []*datapb.FieldBinlog, collectionID, partitionID, targetSegmentID int64) ([]*datapb.FieldBinlog, error) {
	ret := make([]*datapb.FieldBinlog, 0, len(binlogs))
	for _, fieldBinlog := range binlogs {
		fieldBinlog = proto.Clone(fieldBinlog).(*datapb.FieldBinlog)
		for _, binlog := range fieldBinlog.Binlogs {
			blobKey := metautil.JoinIDPath(collectionID, partitionID, targetSegmentID, binlog.LogID)
			blobPath := path.Join(m.chunkManager.RootPath(), common.SegmentDeltaLogPath, blobKey)
			blob, err := m.chunkManager.Read(m.ctx, binlog.LogPath)
			if err != nil {
				return nil, err
			}
			err = m.chunkManager.Write(m.ctx, blobPath, blob)
			if err != nil {
				return nil, err
			}
			binlog.LogPath = blobPath
		}
		ret = append(ret, fieldBinlog)
	}
	return ret, nil
}

func (m *meta) alterMetaStoreAfterCompaction(modSegments []*SegmentInfo, newSegment *SegmentInfo) error {
	var modSegIDs []int64
	for _, seg := range modSegments {
		modSegIDs = append(modSegIDs, seg.GetID())
	}
	log.Info("meta update: alter meta store for compaction updates",
		zap.Int64s("compact from segments (segments to be updated as dropped)", modSegIDs),
		zap.Int64("new segmentId", newSegment.GetID()),
		zap.Int("binlog", len(newSegment.GetBinlogs())),
		zap.Int("stats log", len(newSegment.GetStatslogs())),
		zap.Int("delta logs", len(newSegment.GetDeltalogs())),
		zap.Int64("compact to segment", newSegment.GetID()))

	m.Lock()
	defer m.Unlock()

	modInfos := lo.Map(modSegments, func(item *SegmentInfo, _ int) *datapb.SegmentInfo {
		return item.SegmentInfo
	})

	if err := m.catalog.AlterSegmentsAndAddNewSegment(m.ctx, modInfos, newSegment.SegmentInfo); err != nil {
		return err
	}

	for _, s := range modSegments {
		m.segments.SetSegment(s.GetID(), s)
	}

	if newSegment.GetNumOfRows() > 0 {
		m.segments.SetSegment(newSegment.GetID(), newSegment)
	}

	return nil
}

func (m *meta) revertAlterMetaStoreAfterCompaction(oldSegments []*SegmentInfo, removalSegment *SegmentInfo) error {
	log.Info("meta update: revert metastore after compaction failure",
		zap.Int64("collectionID", removalSegment.CollectionID),
		zap.Int64("partitionID", removalSegment.PartitionID),
		zap.Int64("compactedTo (segment to remove)", removalSegment.ID),
		zap.Int64s("compactedFrom (segments to add back)", removalSegment.GetCompactionFrom()),
	)

	m.Lock()
	defer m.Unlock()

	oldSegmentInfos := lo.Map(oldSegments, func(item *SegmentInfo, _ int) *datapb.SegmentInfo {
		return item.SegmentInfo
	})

	if err := m.catalog.RevertAlterSegmentsAndAddNewSegment(m.ctx, oldSegmentInfos, removalSegment.SegmentInfo); err != nil {
		return err
	}

	for _, s := range oldSegments {
		m.segments.SetSegment(s.GetID(), s)
	}

	if removalSegment.GetNumOfRows() > 0 {
		m.segments.DropSegment(removalSegment.GetID())
	}
	return nil
}

func (m *meta) updateBinlogs(origin []*datapb.FieldBinlog, removes []*datapb.FieldBinlog, adds []*datapb.FieldBinlog) []*datapb.FieldBinlog {
	fieldBinlogs := make(map[int64]map[string]*datapb.Binlog)
	for _, f := range origin {
		fid := f.GetFieldID()
		if _, ok := fieldBinlogs[fid]; !ok {
			fieldBinlogs[fid] = make(map[string]*datapb.Binlog)
		}
		for _, p := range f.GetBinlogs() {
			fieldBinlogs[fid][p.GetLogPath()] = p
		}
	}

	for _, f := range removes {
		fid := f.GetFieldID()
		if _, ok := fieldBinlogs[fid]; !ok {
			continue
		}
		for _, p := range f.GetBinlogs() {
			delete(fieldBinlogs[fid], p.GetLogPath())
		}
	}

	for _, f := range adds {
		fid := f.GetFieldID()
		if _, ok := fieldBinlogs[fid]; !ok {
			fieldBinlogs[fid] = make(map[string]*datapb.Binlog)
		}
		for _, p := range f.GetBinlogs() {
			fieldBinlogs[fid][p.GetLogPath()] = p
		}
	}

	res := make([]*datapb.FieldBinlog, 0, len(fieldBinlogs))
	for fid, logs := range fieldBinlogs {
		if len(logs) == 0 {
			continue
		}

		binlogs := make([]*datapb.Binlog, 0, len(logs))
		for _, log := range logs {
			binlogs = append(binlogs, log)
		}

		field := &datapb.FieldBinlog{FieldID: fid, Binlogs: binlogs}
		res = append(res, field)
	}
	return res
}

func (m *meta) updateDeltalogs(origin []*datapb.FieldBinlog, removes []*datapb.FieldBinlog, adds []*datapb.FieldBinlog) []*datapb.FieldBinlog {
	res := make([]*datapb.FieldBinlog, 0, len(origin))
	for _, fbl := range origin {
		logs := make(map[string]*datapb.Binlog)
		for _, d := range fbl.GetBinlogs() {
			logs[d.GetLogPath()] = d
		}
		for _, remove := range removes {
			if remove.GetFieldID() == fbl.GetFieldID() {
				for _, r := range remove.GetBinlogs() {
					delete(logs, r.GetLogPath())
				}
			}
		}
		binlogs := make([]*datapb.Binlog, 0, len(logs))
		for _, l := range logs {
			binlogs = append(binlogs, l)
		}
		if len(binlogs) > 0 {
			res = append(res, &datapb.FieldBinlog{
				FieldID: fbl.GetFieldID(),
				Binlogs: binlogs,
			})
		}
	}

	return res
}

// buildSegment utility function for compose datapb.SegmentInfo struct with provided info
func buildSegment(collectionID UniqueID, partitionID UniqueID, segmentID UniqueID, channelName string, isImporting bool) *SegmentInfo {
	info := &datapb.SegmentInfo{
		ID:            segmentID,
		CollectionID:  collectionID,
		PartitionID:   partitionID,
		InsertChannel: channelName,
		NumOfRows:     0,
		State:         commonpb.SegmentState_Growing,
		IsImporting:   isImporting,
	}
	return NewSegmentInfo(info)
}

func isSegmentHealthy(segment *SegmentInfo) bool {
	return segment != nil &&
		segment.GetState() != commonpb.SegmentState_SegmentStateNone &&
		segment.GetState() != commonpb.SegmentState_NotExist &&
		segment.GetState() != commonpb.SegmentState_Dropped
}

func (m *meta) HasSegments(segIDs []UniqueID) (bool, error) {
	m.RLock()
	defer m.RUnlock()

	for _, segID := range segIDs {
		if _, ok := m.segments.segments[segID]; !ok {
			return false, fmt.Errorf("segment is not exist with ID = %d", segID)
		}
	}
	return true, nil
}

func (m *meta) GetCompactionTo(segmentID int64) *SegmentInfo {
	m.RLock()
	defer m.RUnlock()

	segments := m.segments.GetSegments()
	for _, segment := range segments {
		parents := typeutil.NewUniqueSet(segment.GetCompactionFrom()...)
		if parents.Contain(segmentID) {
			return segment
		}
	}
	return nil
}

// UpdateChannelCheckpoint updates and saves channel checkpoint.
func (m *meta) UpdateChannelCheckpoint(vChannel string, pos *internalpb.MsgPosition) error {
	if pos == nil {
		return fmt.Errorf("channelCP is nil, vChannel=%s", vChannel)
	}

	m.Lock()
	defer m.Unlock()

	oldPosition, ok := m.channelCPs[vChannel]
	if !ok || oldPosition.Timestamp < pos.Timestamp {
		err := m.catalog.SaveChannelCheckpoint(m.ctx, vChannel, pos)
		if err != nil {
			return err
		}
		m.channelCPs[vChannel] = pos
		ts, _ := tsoutil.ParseTS(pos.Timestamp)
		log.Debug("UpdateChannelCheckpoint done", zap.String("vChannel", vChannel), zap.Time("time", ts))
	}
	return nil
}

func (m *meta) GetChannelCheckpoint(vChannel string) *internalpb.MsgPosition {
	m.RLock()
	defer m.RUnlock()
	if m.channelCPs[vChannel] == nil {
		return nil
	}
	return proto.Clone(m.channelCPs[vChannel]).(*internalpb.MsgPosition)
}

func (m *meta) DropChannelCheckpoint(vChannel string) error {
	m.Lock()
	defer m.Unlock()
	err := m.catalog.DropChannelCheckpoint(m.ctx, vChannel)
	if err != nil {
		return err
	}
	delete(m.channelCPs, vChannel)
	log.Debug("DropChannelCheckpoint done", zap.String("vChannel", vChannel))
	return nil
}

func (m *meta) GcConfirm(ctx context.Context, collectionID, partitionID UniqueID) bool {
	return m.catalog.GcConfirm(ctx, collectionID, partitionID)
}

// addNewSeg update metrics update for a new segment.
func (s *segMetricMutation) addNewSeg(state commonpb.SegmentState, rowCount int64) {
	s.stateChange[state.String()]++
	s.rowCountChange += rowCount
	s.rowCountAccChange += rowCount
}

// commit persists all updates in current segMetricMutation, should and must be called AFTER segment state change
// has persisted in Etcd.
func (s *segMetricMutation) commit() {
	for state, change := range s.stateChange {
		metrics.DataCoordNumSegments.WithLabelValues(state).Add(float64(change))
	}
	metrics.DataCoordNumStoredRows.WithLabelValues().Add(float64(s.rowCountChange))
	metrics.DataCoordNumStoredRowsCounter.WithLabelValues().Add(float64(s.rowCountAccChange))
}

// append updates current segMetricMutation when segment state change happens.
func (s *segMetricMutation) append(oldState, newState commonpb.SegmentState, rowCountUpdate int64) {
	if oldState != newState {
		s.stateChange[oldState.String()]--
		s.stateChange[newState.String()]++
	}
	// Update # of rows on new flush operations and drop operations.
	if isFlushState(newState) && !isFlushState(oldState) {
		// If new flush.
		s.rowCountChange += rowCountUpdate
		s.rowCountAccChange += rowCountUpdate
	} else if newState == commonpb.SegmentState_Dropped && oldState != newState {
		// If new drop.
		s.rowCountChange -= rowCountUpdate
	}
}

func isFlushState(state commonpb.SegmentState) bool {
	return state == commonpb.SegmentState_Flushing || state == commonpb.SegmentState_Flushed
}

// updateSegStateAndPrepareMetrics updates a segment's in-memory state and prepare for the corresponding metric update.
func updateSegStateAndPrepareMetrics(segToUpdate *SegmentInfo, targetState commonpb.SegmentState, metricMutation *segMetricMutation) {
	log.Debug("updating segment state and updating metrics",
		zap.Int64("segment ID", segToUpdate.GetID()),
		zap.String("old state", segToUpdate.GetState().String()),
		zap.String("new state", targetState.String()),
		zap.Int64("# of rows", segToUpdate.GetNumOfRows()))
	metricMutation.append(segToUpdate.GetState(), targetState, segToUpdate.GetNumOfRows())
	segToUpdate.State = targetState
}