// append the given entries to the raft log. Takes the previous value
// of r.lastIndex and returns a new value. We do this rather than
// modifying r.lastIndex directly because this modification needs to
// be atomic with the commit of the batch.
func (r *Replica) append(batch engine.Engine, prevLastIndex uint64, entries []raftpb.Entry) (uint64, error) {
	if len(entries) == 0 {
		return prevLastIndex, nil
	}
	for i := range entries {
		ent := &entries[i]
		key := keys.RaftLogKey(r.RangeID, ent.Index)
		if err := engine.MVCCPutProto(batch, nil, key, roachpb.ZeroTimestamp, nil, ent); err != nil {
			return 0, err
		}
	}
	lastIndex := entries[len(entries)-1].Index
	// Delete any previously appended log entries which never committed.
	for i := lastIndex + 1; i <= prevLastIndex; i++ {
		err := engine.MVCCDelete(batch, nil,
			keys.RaftLogKey(r.RangeID, i), roachpb.ZeroTimestamp, nil)
		if err != nil {
			return 0, err
		}
	}

	// Commit the batch and update the last index.
	if err := setLastIndex(batch, r.RangeID, lastIndex); err != nil {
		return 0, err
	}

	return lastIndex, nil
}

// append the given entries to the raft log. Takes the previous values of
// r.mu.lastIndex and r.mu.raftLogSize, and returns new values. We do this
// rather than modifying them directly because these modifications need to be
// atomic with the commit of the batch.
func (r *Replica) append(batch engine.ReadWriter, prevLastIndex uint64, prevRaftLogSize int64, entries []raftpb.Entry) (uint64, int64, error) {
	if len(entries) == 0 {
		return prevLastIndex, prevRaftLogSize, nil
	}
	var diff enginepb.MVCCStats
	ctx := context.Background()
	for i := range entries {
		ent := &entries[i]
		key := keys.RaftLogKey(r.RangeID, ent.Index)
		if err := engine.MVCCPutProto(ctx, batch, &diff, key, hlc.ZeroTimestamp, nil /* txn */, ent); err != nil {
			return 0, 0, err
		}
	}
	lastIndex := entries[len(entries)-1].Index
	// Delete any previously appended log entries which never committed.
	for i := lastIndex + 1; i <= prevLastIndex; i++ {
		err := engine.MVCCDelete(ctx, batch, &diff, keys.RaftLogKey(r.RangeID, i),
			hlc.ZeroTimestamp, nil /* txn */)
		if err != nil {
			return 0, 0, err
		}
	}

	if err := setLastIndex(batch, r.RangeID, lastIndex); err != nil {
		return 0, 0, err
	}

	raftLogSize := prevRaftLogSize + diff.SysBytes

	return lastIndex, raftLogSize, nil
}

// append the given entries to the raft log.
func (r *Replica) append(batch engine.Engine, entries []raftpb.Entry) error {
	if len(entries) == 0 {
		return nil
	}
	for _, ent := range entries {
		err := engine.MVCCPutProto(batch, nil, keys.RaftLogKey(r.RangeID, ent.Index),
			roachpb.ZeroTimestamp, nil, &ent)
		if err != nil {
			return err
		}
	}
	lastIndex := entries[len(entries)-1].Index
	prevLastIndex := atomic.LoadUint64(&r.lastIndex)
	// Delete any previously appended log entries which never committed.
	for i := lastIndex + 1; i <= prevLastIndex; i++ {
		err := engine.MVCCDelete(batch, nil,
			keys.RaftLogKey(r.RangeID, i), roachpb.ZeroTimestamp, nil)
		if err != nil {
			return err
		}
	}

	// Commit the batch and update the last index.
	if err := setLastIndex(batch, r.RangeID, lastIndex); err != nil {
		return err
	}
	batch.Defer(func() {
		atomic.StoreUint64(&r.lastIndex, lastIndex)
	})

	return nil
}

// append the given entries to the raft log. Takes the previous value
// of r.lastIndex and returns a new value. We do this rather than
// modifying r.lastIndex directly because this modification needs to
// be atomic with the commit of the batch.
func (r *Replica) append(batch engine.ReadWriter, prevLastIndex uint64, entries []raftpb.Entry) (uint64, error) {
	if len(entries) == 0 {
		return prevLastIndex, nil
	}
	for i := range entries {
		ent := &entries[i]
		key := keys.RaftLogKey(r.RangeID, ent.Index)
		if err := engine.MVCCPutProto(context.Background(), batch, nil, key, hlc.ZeroTimestamp, nil, ent); err != nil {
			return 0, err
		}
	}
	lastIndex := entries[len(entries)-1].Index
	// Delete any previously appended log entries which never committed.
	for i := lastIndex + 1; i <= prevLastIndex; i++ {
		err := engine.MVCCDelete(context.Background(), batch, nil,
			keys.RaftLogKey(r.RangeID, i), hlc.ZeroTimestamp, nil)
		if err != nil {
			return 0, err
		}
	}

	if err := setLastIndex(batch, r.RangeID, lastIndex); err != nil {
		return 0, err
	}

	return lastIndex, nil
}

// Del removes all abort cache entries for the given transaction.
func (sc *AbortCache) Del(
	ctx context.Context,
	e engine.Engine,
	ms *engine.MVCCStats,
	txnID *uuid.UUID,
) error {
	key := keys.AbortCacheKey(sc.rangeID, txnID)
	return engine.MVCCDelete(ctx, e, ms, key, roachpb.ZeroTimestamp, nil /* txn */)
}

// append the given entries to the raft log. Takes the previous values of
// r.mu.lastIndex and r.mu.raftLogSize, and returns new values. We do this
// rather than modifying them directly because these modifications need to be
// atomic with the commit of the batch.
func (r *Replica) append(
	ctx context.Context,
	batch engine.ReadWriter,
	prevLastIndex uint64,
	prevRaftLogSize int64,
	entries []raftpb.Entry,
) (uint64, int64, error) {
	if len(entries) == 0 {
		return prevLastIndex, prevRaftLogSize, nil
	}
	var diff enginepb.MVCCStats
	var value roachpb.Value
	for i := range entries {
		ent := &entries[i]
		key := keys.RaftLogKey(r.RangeID, ent.Index)
		if err := value.SetProto(ent); err != nil {
			return 0, 0, err
		}
		value.InitChecksum(key)
		var err error
		if ent.Index > prevLastIndex {
			err = engine.MVCCBlindPut(ctx, batch, &diff, key, hlc.ZeroTimestamp, value, nil /* txn */)
		} else {
			err = engine.MVCCPut(ctx, batch, &diff, key, hlc.ZeroTimestamp, value, nil /* txn */)
		}
		if err != nil {
			return 0, 0, err
		}
	}

	// Delete any previously appended log entries which never committed.
	lastIndex := entries[len(entries)-1].Index
	for i := lastIndex + 1; i <= prevLastIndex; i++ {
		err := engine.MVCCDelete(ctx, batch, &diff, keys.RaftLogKey(r.RangeID, i),
			hlc.ZeroTimestamp, nil /* txn */)
		if err != nil {
			return 0, 0, err
		}
	}

	if err := setLastIndex(ctx, batch, r.RangeID, lastIndex); err != nil {
		return 0, 0, err
	}

	raftLogSize := prevRaftLogSize + diff.SysBytes

	return lastIndex, raftLogSize, nil
}

// Append implements the multiraft.WriteableGroupStorage interface.
func (r *Replica) Append(entries []raftpb.Entry) error {
	if len(entries) == 0 {
		return nil
	}
	batch := r.rm.Engine().NewBatch()
	defer batch.Close()

	rangeID := r.Desc().RangeID

	for _, ent := range entries {
		err := engine.MVCCPutProto(batch, nil, keys.RaftLogKey(rangeID, ent.Index),
			proto.ZeroTimestamp, nil, &ent)
		if err != nil {
			return err
		}
	}
	lastIndex := entries[len(entries)-1].Index
	prevLastIndex := atomic.LoadUint64(&r.lastIndex)
	// Delete any previously appended log entries which never committed.
	for i := lastIndex + 1; i <= prevLastIndex; i++ {
		err := engine.MVCCDelete(batch, nil,
			keys.RaftLogKey(rangeID, i), proto.ZeroTimestamp, nil)
		if err != nil {
			return err
		}
	}

	// Commit the batch and update the last index.
	if err := setLastIndex(batch, rangeID, lastIndex); err != nil {
		return err
	}
	if err := batch.Commit(); err != nil {
		return err
	}

	atomic.StoreUint64(&r.lastIndex, lastIndex)
	return nil
}

// ApplySnapshot implements the multiraft.WriteableGroupStorage interface.
func (r *Range) ApplySnapshot(snap raftpb.Snapshot) error {
	snapData := proto.RaftSnapshotData{}
	err := gogoproto.Unmarshal(snap.Data, &snapData)
	if err != nil {
		return err
	}

	// First, save the HardState.  The HardState must not be changed
	// because it may record a previous vote cast by this node.
	hardStateKey := keys.RaftHardStateKey(r.Desc().RaftID)
	hardState, _, err := engine.MVCCGet(r.rm.Engine(), hardStateKey, proto.ZeroTimestamp, true /* consistent */, nil)
	if err != nil {
		return err
	}

	// Extract the updated range descriptor.
	desc := snapData.RangeDescriptor

	batch := r.rm.Engine().NewBatch()
	defer batch.Close()

	// Delete everything in the range and recreate it from the snapshot.
	for iter := newRangeDataIterator(&desc, r.rm.Engine()); iter.Valid(); iter.Next() {
		if err := batch.Clear(iter.Key()); err != nil {
			return err
		}
	}

	// Write the snapshot into the range.
	for _, kv := range snapData.KV {
		if err := batch.Put(kv.Key, kv.Value); err != nil {
			return err
		}
	}

	// Restore the saved HardState.
	if hardState == nil {
		err := engine.MVCCDelete(batch, nil, hardStateKey, proto.ZeroTimestamp, nil)
		if err != nil {
			return err
		}
	} else {
		err := engine.MVCCPut(batch, nil, hardStateKey, proto.ZeroTimestamp, *hardState, nil)
		if err != nil {
			return err
		}
	}

	// Read the leader lease.
	lease, err := loadLeaderLease(batch, desc.RaftID)
	if err != nil {
		return err
	}

	// Copy range stats to new range.
	oldStats := r.stats
	r.stats, err = newRangeStats(desc.RaftID, batch)
	if err != nil {
		r.stats = oldStats
		return err
	}

	// The next line sets the persisted last index to the last applied index.
	// This is not a correctness issue, but means that we may have just
	// transferred some entries we're about to re-request from the leader and
	// overwrite.
	// However, raft.MultiNode currently expects this behaviour, and the
	// performance implications are not likely to be drastic. If our feelings
	// about this ever change, we can add a LastIndex field to
	// raftpb.SnapshotMetadata.
	if err := setLastIndex(batch, r.Desc().RaftID, snap.Metadata.Index); err != nil {
		return err
	}

	if err := batch.Commit(); err != nil {
		return err
	}

	// As outlined above, last and applied index are the same after applying
	// the snapshot.
	atomic.StoreUint64(&r.lastIndex, snap.Metadata.Index)
	atomic.StoreUint64(&r.appliedIndex, snap.Metadata.Index)

	// Atomically update the descriptor and lease.
	if err := r.setDesc(&desc); err != nil {
		return err
	}
	atomic.StorePointer(&r.lease, unsafe.Pointer(lease))
	return nil
}

// applySnapshot updates the replica based on the given snapshot.
// Returns the new last index.
func (r *Replica) applySnapshot(batch engine.Engine, snap raftpb.Snapshot) (uint64, error) {
	snapData := roachpb.RaftSnapshotData{}
	err := proto.Unmarshal(snap.Data, &snapData)
	if err != nil {
		return 0, err
	}

	rangeID := r.RangeID

	// First, save the HardState. The HardState must not be changed
	// because it may record a previous vote cast by this node. This is
	// usually unnecessary because a snapshot is nearly always
	// accompanied by a new HardState which incorporates both our former
	// state and new information from the leader, but in the event that
	// the HardState has not changed, we want to use our own previous
	// HardState and not one that was transmitted via the snapshot.
	hardStateKey := keys.RaftHardStateKey(rangeID)
	hardState, _, err := engine.MVCCGet(batch, hardStateKey, roachpb.ZeroTimestamp, true /* consistent */, nil)
	if err != nil {
		return 0, err
	}

	// Extract the updated range descriptor.
	desc := snapData.RangeDescriptor

	// Delete everything in the range and recreate it from the snapshot.
	// We need to delete any old Raft log entries here because any log entries
	// that predate the snapshot will be orphaned and never truncated or GC'd.
	iter := newReplicaDataIterator(&desc, batch, false /* !replicatedOnly */)
	defer iter.Close()
	for ; iter.Valid(); iter.Next() {
		if err := batch.Clear(iter.Key()); err != nil {
			return 0, err
		}
	}

	// Determine the unreplicated key prefix so we can drop any
	// unreplicated keys from the snapshot.
	unreplicatedPrefix := keys.MakeRangeIDUnreplicatedPrefix(desc.RangeID)

	// Write the snapshot into the range.
	for _, kv := range snapData.KV {
		if bytes.HasPrefix(kv.Key, unreplicatedPrefix) {
			continue
		}
		mvccKey := engine.MVCCKey{
			Key:       kv.Key,
			Timestamp: kv.Timestamp,
		}
		if err := batch.Put(mvccKey, kv.Value); err != nil {
			return 0, err
		}
	}

	// Write the snapshot's Raft log into the range.
	if _, err := r.append(batch, 0, snapData.LogEntries); err != nil {
		return 0, err
	}

	// Restore the saved HardState.
	if hardState == nil {
		err := engine.MVCCDelete(batch, nil, hardStateKey, roachpb.ZeroTimestamp, nil)
		if err != nil {
			return 0, err
		}
	} else {
		err := engine.MVCCPut(batch, nil, hardStateKey, roachpb.ZeroTimestamp, *hardState, nil)
		if err != nil {
			return 0, err
		}
	}

	// Read the leader lease.
	lease, err := loadLeaderLease(batch, desc.RangeID)
	if err != nil {
		return 0, err
	}

	// Load updated range stats. The local newStats variable will be assigned
	// to r.stats after the batch commits.
	newStats, err := newRangeStats(desc.RangeID, batch)
	if err != nil {
		return 0, err
	}

	// The next line sets the persisted last index to the last applied index.
	// This is not a correctness issue, but means that we may have just
	// transferred some entries we're about to re-request from the leader and
	// overwrite.
	// However, raft.MultiNode currently expects this behaviour, and the
	// performance implications are not likely to be drastic. If our feelings
	// about this ever change, we can add a LastIndex field to
	// raftpb.SnapshotMetadata.
	if err := setLastIndex(batch, rangeID, snap.Metadata.Index); err != nil {
		return 0, err
	}

	batch.Defer(func() {
//.........这里部分代码省略.........

// Delete deletes the key and value specified by key.
func (r *Range) Delete(batch engine.Engine, ms *engine.MVCCStats, args *proto.DeleteRequest, reply *proto.DeleteResponse) {
	reply.SetGoError(engine.MVCCDelete(batch, ms, args.Key, args.Timestamp, args.Txn))
}

// Delete deletes the key and value specified by key.
func (r *Range) Delete(batch engine.Engine, ms *engine.MVCCStats, args proto.DeleteRequest) (proto.DeleteResponse, error) {
	var reply proto.DeleteResponse

	return reply, engine.MVCCDelete(batch, ms, args.Key, args.Timestamp, args.Txn)
}

// applySnapshot updates the replica based on the given snapshot.
func (r *Replica) applySnapshot(snap raftpb.Snapshot) error {
	snapData := roachpb.RaftSnapshotData{}
	err := proto.Unmarshal(snap.Data, &snapData)
	if err != nil {
		return err
	}

	rangeID := r.Desc().RangeID

	// First, save the HardState.  The HardState must not be changed
	// because it may record a previous vote cast by this node.
	hardStateKey := keys.RaftHardStateKey(rangeID)
	hardState, _, err := engine.MVCCGet(r.store.Engine(), hardStateKey, roachpb.ZeroTimestamp, true /* consistent */, nil)
	if err != nil {
		return err
	}

	// Extract the updated range descriptor.
	desc := snapData.RangeDescriptor

	batch := r.store.Engine().NewBatch()
	defer batch.Close()

	// Delete everything in the range and recreate it from the snapshot.
	iter := newReplicaDataIterator(&desc, r.store.Engine())
	defer iter.Close()
	for ; iter.Valid(); iter.Next() {
		if err := batch.Clear(iter.Key()); err != nil {
			return err
		}
	}

	// Write the snapshot into the range.
	for _, kv := range snapData.KV {
		mvccKey := engine.MVCCKey{
			Key:       kv.Key,
			Timestamp: kv.Timestamp,
		}
		if err := batch.Put(mvccKey, kv.Value); err != nil {
			return err
		}
	}

	// Restore the saved HardState.
	if hardState == nil {
		err := engine.MVCCDelete(batch, nil, hardStateKey, roachpb.ZeroTimestamp, nil)
		if err != nil {
			return err
		}
	} else {
		err := engine.MVCCPut(batch, nil, hardStateKey, roachpb.ZeroTimestamp, *hardState, nil)
		if err != nil {
			return err
		}
	}

	// Read the leader lease.
	lease, err := loadLeaderLease(batch, desc.RangeID)
	if err != nil {
		return err
	}

	// Load updated range stats. The local newStats variable will be assigned
	// to r.stats after the batch commits.
	newStats, err := newRangeStats(desc.RangeID, batch)
	if err != nil {
		return err
	}

	// The next line sets the persisted last index to the last applied index.
	// This is not a correctness issue, but means that we may have just
	// transferred some entries we're about to re-request from the leader and
	// overwrite.
	// However, raft.MultiNode currently expects this behaviour, and the
	// performance implications are not likely to be drastic. If our feelings
	// about this ever change, we can add a LastIndex field to
	// raftpb.SnapshotMetadata.
	if err := setLastIndex(batch, rangeID, snap.Metadata.Index); err != nil {
		return err
	}

	if err := batch.Commit(); err != nil {
		return err
	}

	// Update the range stats.
	r.stats.Replace(newStats)

	// As outlined above, last and applied index are the same after applying
	// the snapshot.
	atomic.StoreUint64(&r.lastIndex, snap.Metadata.Index)
	atomic.StoreUint64(&r.appliedIndex, snap.Metadata.Index)

	// Atomically update the descriptor and lease.
	if err := r.setDesc(&desc); err != nil {
		return err
	}
	// Update other fields which are uninitialized or need updating.
	// This may not happen if the system config has not yet been loaded.
//.........这里部分代码省略.........