Golang Engine.Defer方法代码示例

// 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
}

// mergeTrigger is called on a successful commit of an AdminMerge
// transaction. It recomputes stats for the receiving range.
func (r *Range) mergeTrigger(batch engine.Engine, merge *proto.MergeTrigger) error {
	if !bytes.Equal(r.Desc().StartKey, merge.UpdatedDesc.StartKey) {
		return util.Errorf("range and updated range start keys do not match: %s != %s",
			r.Desc().StartKey, merge.UpdatedDesc.StartKey)
	}

	if !r.Desc().EndKey.Less(merge.UpdatedDesc.EndKey) {
		return util.Errorf("range end key is not less than the post merge end key: %s >= %s",
			r.Desc().EndKey, merge.UpdatedDesc.EndKey)
	}

	if merge.SubsumedRaftID <= 0 {
		return util.Errorf("subsumed raft ID must be provided: %d", merge.SubsumedRaftID)
	}

	// Copy the subsumed range's response cache to the subsuming one.
	if err := r.respCache.CopyFrom(batch, merge.SubsumedRaftID); err != nil {
		return util.Errorf("unable to copy response cache to new split range: %s", err)
	}

	// Compute stats for updated range.
	now := r.rm.Clock().Timestamp()
	iter := newRangeDataIterator(&merge.UpdatedDesc, batch)
	ms, err := engine.MVCCComputeStats(iter, now.WallTime)
	iter.Close()
	if err != nil {
		return util.Errorf("unable to compute stats for the range after merge: %s", err)
	}
	if err = r.stats.SetMVCCStats(batch, ms); err != nil {
		return util.Errorf("unable to write MVCC stats: %s", err)
	}

	// Clear the timestamp cache. In the case that this replica and the
	// subsumed replica each held their respective leader leases, we
	// could merge the timestamp caches for efficiency. But it's unlikely
	// and not worth the extra logic and potential for error.
	r.Lock()
	r.tsCache.Clear(r.rm.Clock())
	r.Unlock()

	batch.Defer(func() {
		if err := r.rm.MergeRange(r, merge.UpdatedDesc.EndKey, merge.SubsumedRaftID); err != nil {
			// Our in-memory state has diverged from the on-disk state.
			log.Fatalf("failed to update store after merging range: %s", err)
		}
	})
	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.........

// splitTrigger is called on a successful commit of an AdminSplit
// transaction. It copies the response cache for the new range and
// recomputes stats for both the existing, updated range and the new
// range.
func (r *Range) splitTrigger(batch engine.Engine, split *proto.SplitTrigger) error {
	if !bytes.Equal(r.Desc().StartKey, split.UpdatedDesc.StartKey) ||
		!bytes.Equal(r.Desc().EndKey, split.NewDesc.EndKey) {
		return util.Errorf("range does not match splits: (%s-%s) + (%s-%s) != %s",
			split.UpdatedDesc.StartKey, split.UpdatedDesc.EndKey,
			split.NewDesc.StartKey, split.NewDesc.EndKey, r)
	}

	// Copy the GC metadata.
	gcMeta, err := r.GetGCMetadata()
	if err != nil {
		return util.Errorf("unable to fetch GC metadata: %s", err)
	}
	if err := engine.MVCCPutProto(batch, nil, keys.RangeGCMetadataKey(split.NewDesc.RaftID), proto.ZeroTimestamp, nil, gcMeta); err != nil {
		return util.Errorf("unable to copy GC metadata: %s", err)
	}

	// Copy the last verification timestamp.
	verifyTS, err := r.GetLastVerificationTimestamp()
	if err != nil {
		return util.Errorf("unable to fetch last verification timestamp: %s", err)
	}
	if err := engine.MVCCPutProto(batch, nil, keys.RangeLastVerificationTimestampKey(split.NewDesc.RaftID), proto.ZeroTimestamp, nil, &verifyTS); err != nil {
		return util.Errorf("unable to copy last verification timestamp: %s", err)
	}

	// Compute stats for updated range.
	now := r.rm.Clock().Timestamp()
	iter := newRangeDataIterator(&split.UpdatedDesc, batch)
	ms, err := engine.MVCCComputeStats(iter, now.WallTime)
	iter.Close()
	if err != nil {
		return util.Errorf("unable to compute stats for updated range after split: %s", err)
	}
	if err := r.stats.SetMVCCStats(batch, ms); err != nil {
		return util.Errorf("unable to write MVCC stats: %s", err)
	}

	// Initialize the new range's response cache by copying the original's.
	if err = r.respCache.CopyInto(batch, split.NewDesc.RaftID); err != nil {
		return util.Errorf("unable to copy response cache to new split range: %s", err)
	}

	// Add the new split range to the store. This step atomically
	// updates the EndKey of the updated range and also adds the
	// new range to the store's range map.
	newRng, err := NewRange(&split.NewDesc, r.rm)
	if err != nil {
		return err
	}

	// Compute stats for new range.
	iter = newRangeDataIterator(&split.NewDesc, batch)
	ms, err = engine.MVCCComputeStats(iter, now.WallTime)
	iter.Close()
	if err != nil {
		return util.Errorf("unable to compute stats for new range after split: %s", err)
	}
	if err = newRng.stats.SetMVCCStats(batch, ms); err != nil {
		return util.Errorf("unable to write MVCC stats: %s", err)
	}

	// Copy the timestamp cache into the new range.
	r.Lock()
	r.tsCache.MergeInto(newRng.tsCache, true /* clear */)
	r.Unlock()

	batch.Defer(func() {
		if err := r.rm.SplitRange(r, newRng); err != nil {
			// Our in-memory state has diverged from the on-disk state.
			log.Fatalf("failed to update Store after split: %s", err)
		}
	})

	return nil
}