2022-02-14 analysis of the startup and request processing process of the incluxdb cluster Coordinator

Catalog

Abstract :

Sequence diagram :

It can be seen that the process is as follows :

Source code processing :

Start the service :

Open up a new collaboration for each new connection :

Read the data and parse the request :

With executeSelectStatement As an example of request processing source code :

---

Abstract :

analysis influxdb Cluster startup and request processing process

Sequence diagram :

It can be seen that the process is as follows :

1.   After starting the service, listen to the corresponding port
2.   After connection is requested , Create a new process to process the data of the connection
   1.   Each connection has a separate coprocessor processing data
3.   Read the data sent by the connection , Resolve request
4.   Make different interface distribution according to the type of request

Source code processing :

Start the service :

// Service processes data received over raw TCP connections.
type Service struct {
	mu sync.RWMutex

	wg      sync.WaitGroup
	closing chan struct{}

	Listener net.Listener

	MetaClient interface {
		ShardOwner(shardID uint64) (string, string, *meta.ShardGroupInfo)
	}

	TSDBStore TSDBStore

	Logger  *zap.Logger
	statMap *expvar.Map
}

// NewService returns a new instance of Service.
func NewService(c Config) *Service {
	return &Service{
		closing: make(chan struct{}),
		//Logger:  log.New(os.Stderr, "[cluster] ", log.LstdFlags),
		Logger:  zap.NewNop(),
		statMap: freetsdb.NewStatistics("cluster", "cluster", nil),
	}
}

// Open opens the network listener and begins serving requests.
func (s *Service) Open() error {

	s.Logger.Info("Starting cluster service")
	// Begin serving conections.
	s.wg.Add(1)
	go s.serve()

	return nil
}

Open up a new collaboration for each new connection :

// serve accepts connections from the listener and handles them.
func (s *Service) serve() {
	defer s.wg.Done()

	for {
		// Check if the service is shutting down.
		select {
		case <-s.closing:
			return
		default:
		}

		// Accept the next connection.
		conn, err := s.Listener.Accept()
		if err != nil {
			if strings.Contains(err.Error(), "connection closed") {
				s.Logger.Info("cluster service accept", zap.Error(err))
				return
			}
			s.Logger.Info("accept", zap.Error(err))
			continue
		}

		// Delegate connection handling to a separate goroutine.
		s.wg.Add(1)
		go func() {
			defer s.wg.Done()
			s.handleConn(conn)
		}()
	}
}

Read the data and parse the request :

// handleConn services an individual TCP connection.
func (s *Service) handleConn(conn net.Conn) {
	// Ensure connection is closed when service is closed.
	closing := make(chan struct{})
	defer close(closing)
	go func() {
		select {
		case <-closing:
		case <-s.closing:
		}
		conn.Close()
	}()

	for {
		// Read type-length-value.
		typ, err := ReadType(conn)
		if err != nil {
			if strings.HasSuffix(err.Error(), "EOF") {
				return
			}
			s.Logger.Info("unable to read type", zap.Error(err))
			return
		}

		// Delegate message processing by type.
		switch typ {
		case writeShardRequestMessage:
			buf, err := ReadLV(conn)
			if err != nil {
				s.Logger.Info("unable to read length-value:", zap.Error(err))
				return
			}

			s.statMap.Add(writeShardReq, 1)
			err = s.processWriteShardRequest(buf)
			if err != nil {
				s.Logger.Info("process write shard error:", zap.Error(err))
			}
			s.writeShardResponse(conn, err)
		case executeStatementRequestMessage:
			buf, err := ReadLV(conn)
			if err != nil {
				s.Logger.Info("unable to read length-value:", zap.Error(err))
				return
			}

			err = s.processExecuteStatementRequest(buf)
			if err != nil {
				s.Logger.Info("process execute statement error:", zap.Error(err))
			}
			s.writeShardResponse(conn, err)
		case createIteratorRequestMessage:
			s.statMap.Add(createIteratorReq, 1)
			s.processCreateIteratorRequest(conn)
			return
		case fieldDimensionsRequestMessage:
			s.statMap.Add(fieldDimensionsReq, 1)
			s.processFieldDimensionsRequest(conn)
			return
		default:
			s.Logger.Info("coordinator service message type not found:", zap.Uint8("Type", uint8(typ)))
		}
	}
}

With executeSelectStatement As an example of request processing source code :

func (e *StatementExecutor) executeSelectStatement(stmt *influxql.SelectStatement, ctx *query.ExecutionContext) error {

	cur, err := e.createIterators(ctx, stmt, ctx.ExecutionOptions)
	if err != nil {
		return err
	}

	// Generate a row emitter from the iterator set.
	em := query.NewEmitter(cur, ctx.ChunkSize)
	defer em.Close()

	// Emit rows to the results channel.
	var writeN int64
	var emitted bool

	var pointsWriter *BufferedPointsWriter
	if stmt.Target != nil {
		pointsWriter = NewBufferedPointsWriter(e.PointsWriter, stmt.Target.Measurement.Database, stmt.Target.Measurement.RetentionPolicy, 10000)
	}

	for {
		row, partial, err := em.Emit()

		if err != nil {
			return err
		} else if row == nil {
			// Check if the query was interrupted while emitting.
			select {
			case <-ctx.Done():
				return ctx.Err()
			default:
			}
			break
		}

		// Write points back into system for INTO statements.
		if stmt.Target != nil {
			n, err := e.writeInto(pointsWriter, stmt, row)
			if err != nil {
				return err
			}
			writeN += n
			continue
		}

		result := &query.Result{
			Series:  []*models.Row{row},
			Partial: partial,
		}

		// Send results or exit if closing.
		if err := ctx.Send(result); err != nil {
			return err
		}

		emitted = true
	}

	// Flush remaining points and emit write count if an INTO statement.
	if stmt.Target != nil {
		if err := pointsWriter.Flush(); err != nil {
			return err
		}

		var messages []*query.Message
		if ctx.ReadOnly {
			messages = append(messages, query.ReadOnlyWarning(stmt.String()))
		}

		return ctx.Send(&query.Result{
			Messages: messages,
			Series: []*models.Row{
   {
				Name:    "result",
				Columns: []string{"time", "written"},
				Values:  [][]interface{}{
   {time.Unix(0, 0).UTC(), writeN}},
			}},
		})
	}

	// Always emit at least one result.
	if !emitted {
		return ctx.Send(&query.Result{
			Series: make([]*models.Row, 0),
		})
	}

	return nil
}

func (e *StatementExecutor) writeInto(w pointsWriter, stmt *influxql.SelectStatement, row *models.Row) (n int64, err error) {
	if stmt.Target.Measurement.Database == "" {
		return 0, errNoDatabaseInTarget
	}

	// It might seem a bit weird that this is where we do this, since we will have to
	// convert rows back to points. The Executors (both aggregate and raw) are complex
	// enough that changing them to write back to the DB is going to be clumsy
	//
	// it might seem weird to have the write be in the Executor, but the interweaving of
	// limitedRowWriter and ExecuteAggregate/Raw makes it ridiculously hard to make sure that the
	// results will be the same as when queried normally.
	name := stmt.Target.Measurement.Name
	if name == "" {
		name = row.Name
	}

	points, err := convertRowToPoints(name, row)
	if err != nil {
		return 0, err
	}

	if err := w.WritePointsInto(&IntoWriteRequest{
		Database:        stmt.Target.Measurement.Database,
		RetentionPolicy: stmt.Target.Measurement.RetentionPolicy,
		Points:          points,
	}); err != nil {
		return 0, err
	}

	return int64(len(points)), nil
}

// writeToShards writes points to a shard and ensures a write consistency level has been met.  If the write
// partially succeeds, ErrPartialWrite is returned.
func (w *PointsWriter) writeToShard(shard *meta.ShardInfo, database, retentionPolicy string,
	consistency ConsistencyLevel, points []models.Point) error {
	atomic.AddInt64(&w.stats.PointWriteReqLocal, int64(len(points)))

	// The required number of writes to achieve the requested consistency level
	required := len(shard.Owners)
	switch consistency {
	case ConsistencyLevelAny, ConsistencyLevelOne:
		required = 1
	case ConsistencyLevelQuorum:
		required = required/2 + 1
	}

	// response channel for each shard writer go routine
	type AsyncWriteResult struct {
		Owner meta.ShardOwner
		Err   error
	}
	ch := make(chan *AsyncWriteResult, len(shard.Owners))

	for _, owner := range shard.Owners {
		go func(shardID uint64, owner meta.ShardOwner, points []models.Point) {
			if w.Node.ID == owner.NodeID {
				atomic.AddInt64(&w.stats.PointWriteReqLocal, int64(len(points)))
				err := w.TSDBStore.WriteToShard(shardID, points)
				// If we've written to shard that should exist on the current node, but the store has
				// not actually created this shard, tell it to create it and retry the write
				if err == tsdb.ErrShardNotFound {
					err = w.TSDBStore.CreateShard(database, retentionPolicy, shardID, true)
					if err != nil {
						ch <- &AsyncWriteResult{owner, err}
						return
					}
					err = w.TSDBStore.WriteToShard(shardID, points)
				}
				ch <- &AsyncWriteResult{owner, err}
				return
			}

			atomic.AddInt64(&w.stats.PointWriteReqRemote, int64(len(points)))
			err := w.ShardWriter.WriteShard(shardID, owner.NodeID, points)
			if err != nil && tsdb.IsRetryable(err) {
				// The remote write failed so queue it via hinted handoff
				atomic.AddInt64(&w.stats.WritePointReqHH, int64(len(points)))
				hherr := w.HintedHandoff.WriteShard(shardID, owner.NodeID, points)
				if hherr != nil {
					ch <- &AsyncWriteResult{owner, hherr}
					return
				}

				// If the write consistency level is ANY, then a successful hinted handoff can
				// be considered a successful write so send nil to the response channel
				// otherwise, let the original error propagate to the response channel
				if hherr == nil && consistency == ConsistencyLevelAny {
					ch <- &AsyncWriteResult{owner, nil}
					return
				}
			}
			ch <- &AsyncWriteResult{owner, err}

		}(shard.ID, owner, points)
	}

	var wrote int
	timeout := time.After(w.WriteTimeout)
	var writeError error
	for range shard.Owners {
		select {
		case <-w.closing:
			return ErrWriteFailed
		case <-timeout:
			atomic.AddInt64(&w.stats.WriteTimeout, 1)
			// return timeout error to caller
			return ErrTimeout
		case result := <-ch:
			// If the write returned an error, continue to the next response
			if result.Err != nil {
				atomic.AddInt64(&w.stats.WriteErr, 1)
				w.Logger.Info("write failed", zap.Uint64("shard", shard.ID), zap.Uint64("node", result.Owner.NodeID), zap.Error(result.Err))

				// Keep track of the first error we see to return back to the client
				if writeError == nil {
					writeError = result.Err
				}
				continue
			}

			wrote++

			// We wrote the required consistency level
			if wrote >= required {
				atomic.AddInt64(&w.stats.WriteOK, 1)
				return nil
			}
		}
	}

	if wrote > 0 {
		atomic.AddInt64(&w.stats.WritePartial, 1)
		return ErrPartialWrite
	}

	if writeError != nil {
		return fmt.Errorf("write failed: %v", writeError)
	}

	return ErrWriteFailed

}