git.giacomolli.uk - onechat/blob - memory.go

   1 package main
   2
   3 import (
   4         "context"
   5         "encoding/json"
   6         "errors"
   7         "fmt"
   8         "log/slog"
   9         "os"
  10         "path/filepath"
  11         "strings"
  12         "sync"
  13         "time"
  14 )
  15
  16 var (
  17         // errMemoryNoView tells that a chat has messages but no saved view.
  18         errMemoryNoView = errors.New("the chat has messages but no saved view")
  19
  20         // errMemoryUnsettled tells that a line of the view stays pending,
  21         // because its build failed.
  22         errMemoryUnsettled = errors.New("a summary of the view failed, and it is tried again at the next message")
  23 )
  24
  25 // Summarizer builds the text of one node with a model.
  26 type Summarizer interface {
  27         Summarize(ctx context.Context, task Task) (string, error)
  28 }
  29
  30 // Memory is the memory of one chat: the message log, the summary tree, the chat
  31 // view, the compaction view, and the queue of the builds. The compaction view
  32 // is the chat view merged further, at the limits of 16 to 32 KB. It takes the
  33 // same new lines, and it merges again in one batch when it is too large or when
  34 // the chat view merges. So the compactions share its prefix in the prompt
  35 // cache. It saves the views to view.json after each change and loads them at
  36 // start. It never builds the views again from the log, because a new view
  37 // differs from the live one and so loses the prompt cache.
  38 //
  39 // Each write goes to the operating system at once, and a syncer makes the
  40 // writes durable by group commit in the background. Flush waits until the
  41 // writes so far are durable.
  42 //
  43 // The summarizer builds the nodes in the queue in the background. The start
  44 // reads the indexes once to fill the queue again. After that, only a new
  45 // message or a new node adds work. Memory keeps the nodes of the views and the
  46 // tasks of the running builds. It reads all other messages and nodes from their
  47 // day files through the indexes.
  48 type Memory struct {
  49         mutex      sync.Mutex
  50         root       string
  51         log        *Log
  52         syncer     *Syncer
  53         tree       *Tree
  54         chat       *View
  55         cview      *View
  56         queue      *BuildQueue
  57         summarizer Summarizer
  58         logger     *slog.Logger
  59         ctx        context.Context
  60         cancel     context.CancelFunc
  61         workers    sync.WaitGroup
  62         changed    chan struct{}
  63 }
  64
  65 // Task is the build of the node (Level, Index). Context is the compaction view
  66 // for the build. Input holds the source "kind: text" of a leaf, or the two
  67 // child lines of a merge with their newlines as spaces. Images holds the leaf
  68 // image filenames and is empty for merges.
  69 type Task struct {
  70         Level   int
  71         Index   int
  72         Context string
  73         Input   []string
  74         Images  []string
  75 }
  76
  77 // MemoryViewFile is the content of view.json.
  78 type MemoryViewFile struct {
  79         Chat       ViewState `json:"chat"`
  80         Compaction ViewState `json:"compaction"`
  81 }
  82
  83 // openMemory opens the chat in root and starts the builds that are ready. The
  84 // clock gives the dates of new messages and the days of new nodes. logger gets
  85 // one line for each failed build. The builds stop when ctx ends or at Close.
  86 func openMemory(ctx context.Context, root string, clock func() time.Time, summarizer Summarizer, logger *slog.Logger) (*Memory, error) {
  87         log, err := openLog(ctx, root, clock)
  88         if err != nil {
  89                 return nil, fmt.Errorf("open memory log: %w", err)
  90         }
  91
  92         m := &Memory{
  93                 root:       root,
  94                 log:        log,
  95                 queue:      newBuildQueue(),
  96                 summarizer: summarizer,
  97                 logger:     logger,
  98                 changed:    make(chan struct{}),
  99         }
 100
 101         m.ctx, m.cancel = context.WithCancel(ctx)
 102
 103         m.syncer, err = openSyncer(root)
 104         if err != nil {
 105                 return nil, errors.Join(err, m.Close())
 106         }
 107
 108         m.tree, err = openTree(ctx, root, log.Len(), clock)
 109         if err != nil {
 110                 return nil, errors.Join(err, m.Close())
 111         }
 112
 113         err = m.load()
 114         if err != nil {
 115                 return nil, errors.Join(fmt.Errorf("load view: %w", err), m.Close())
 116         }
 117
 118         err = m.restoreQueue()
 119         if err != nil {
 120                 return nil, errors.Join(fmt.Errorf("restore build queue: %w", err), m.Close())
 121         }
 122
 123         err = m.catchUp()
 124         if err != nil {
 125                 return nil, errors.Join(err, m.Close())
 126         }
 127
 128         m.mutex.Lock()
 129         m.syncer.Written()
 130         m.dispatch()
 131         m.mutex.Unlock()
 132
 133         return m, nil
 134 }
 135
 136 // Close stops the builds, waits for them, makes the writes durable, closes the
 137 // files of the chat, and releases its lock.
 138 func (m *Memory) Close() error {
 139         m.cancel()
 140         m.workers.Wait()
 141
 142         m.mutex.Lock()
 143         defer m.mutex.Unlock()
 144
 145         var err error
 146
 147         if m.syncer != nil {
 148                 err = m.syncer.Close()
 149         }
 150
 151         if m.tree != nil {
 152                 err = errors.Join(err, m.tree.Close())
 153         }
 154
 155         return errors.Join(err, m.log.Close())
 156 }
 157
 158 // load reads the saved views.
 159 func (m *Memory) load() error {
 160         data, err := os.ReadFile(m.viewPath())
 161         if errors.Is(err, os.ErrNotExist) && m.log.Len() == 0 {
 162                 m.chat = newView(viewChatHigh, viewChatLow)
 163                 m.cview = newView(viewCompactionHigh, viewCompactionLow)
 164
 165                 return nil
 166         }
 167
 168         if errors.Is(err, os.ErrNotExist) {
 169                 return errMemoryNoView
 170         }
 171
 172         if err != nil {
 173                 return fmt.Errorf("read view: %w", err)
 174         }
 175
 176         var file MemoryViewFile
 177
 178         err = json.Unmarshal(data, &file)
 179         if err != nil {
 180                 return fmt.Errorf("decode view: %w", err)
 181         }
 182
 183         m.chat, err = restoreView(file.Chat, viewChatHigh, viewChatLow, m.tree)
 184         if err != nil {
 185                 return fmt.Errorf("chat view: %w", err)
 186         }
 187
 188         m.cview, err = restoreView(file.Compaction, viewCompactionHigh, viewCompactionLow, m.tree)
 189         if err != nil {
 190                 return fmt.Errorf("compaction view: %w", err)
 191         }
 192
 193         if m.cview.end != m.chat.end {
 194                 return fmt.Errorf("compaction view covers %d messages, but the chat view %d", m.cview.end, m.chat.end)
 195         }
 196
 197         if m.chat.end > m.log.Len() {
 198                 return fmt.Errorf("view covers %d messages, but the log has %d", m.chat.end, m.log.Len())
 199         }
 200
 201         return nil
 202 }
 203
 204 // restoreQueue adds the work of the messages in the view to the queue. It
 205 // builds each node that needs no model call and that a crash left out.
 206 func (m *Memory) restoreQueue() error {
 207         for id := range m.chat.end {
 208                 built, err := m.tree.Built(0, id)
 209                 if err != nil {
 210                         return fmt.Errorf("check restored leaf: %w", err)
 211                 }
 212
 213                 if built {
 214                         continue
 215                 }
 216
 217                 message, err := m.log.Message(id)
 218                 if err != nil {
 219                         return fmt.Errorf("read restored message: %w", err)
 220                 }
 221
 222                 leaf, free := freeLeaf(message)
 223                 if !free {
 224                         m.queue.AddLeaf(id)
 225
 226                         continue
 227                 }
 228
 229                 err = m.build(leaf)
 230                 if err != nil {
 231                         return fmt.Errorf("build restored leaf: %w", err)
 232                 }
 233         }
 234
 235         keys, err := m.tree.Keys()
 236         if err != nil {
 237                 return fmt.Errorf("read built nodes: %w", err)
 238         }
 239
 240         for _, key := range keys {
 241                 if key.index%2 != 0 {
 242                         continue
 243                 }
 244
 245                 err = m.settle(key)
 246                 if err != nil {
 247                         return fmt.Errorf("settle restored node: %w", err)
 248                 }
 249         }
 250
 251         return nil
 252 }
 253
 254 // catchUp adds the messages that the view does not cover yet. A crash can stop
 255 // an append after the log write and before the view save.
 256 func (m *Memory) catchUp() error {
 257         if m.chat.end == m.log.Len() {
 258                 return nil
 259         }
 260
 261         for m.chat.end < m.log.Len() {
 262                 message, err := m.log.Message(m.chat.end)
 263                 if err != nil {
 264                         return fmt.Errorf("read pending message: %w", err)
 265                 }
 266
 267                 err = m.addMessage(message)
 268                 if err != nil {
 269                         return fmt.Errorf("add pending message: %w", err)
 270                 }
 271         }
 272
 273         err := m.save()
 274         if err != nil {
 275                 return fmt.Errorf("save caught-up memory: %w", err)
 276         }
 277
 278         return nil
 279 }
 280
 281 // dispatch starts the builds that are ready, up to the limit. A build whose
 282 // input cannot be read fails and waits for the next message.
 283 func (m *Memory) dispatch() {
 284         for m.ctx.Err() == nil {
 285                 key, ready := m.queue.Next()
 286                 if !ready {
 287                         return
 288                 }
 289
 290                 task, err := m.task(key)
 291                 if err != nil {
 292                         m.failed(key, fmt.Errorf("read its input: %w", err))
 293                         m.queue.Fail(key)
 294
 295                         continue
 296                 }
 297
 298                 m.workers.Add(1)
 299
 300                 go m.run(key, task)
 301         }
 302 }
 303
 304 func (m *Memory) viewPath() string {
 305         return filepath.Join(m.root, "view.json")
 306 }
 307
 308 // build adds node to the tree, keeps it in the views when it is a pending line,
 309 // and settles its parent.
 310 func (m *Memory) build(node Node) error {
 311         err := m.tree.Add(node)
 312         if err != nil {
 313                 return fmt.Errorf("add built node: %w", err)
 314         }
 315
 316         m.chat.Refresh(node)
 317         m.cview.Refresh(node)
 318
 319         err = m.settle(NodeKey{node.Level, node.Index})
 320         if err != nil {
 321                 return fmt.Errorf("settle built node: %w", err)
 322         }
 323
 324         return nil
 325 }
 326
 327 // settle looks at the parent of the built node key when both children are
 328 // built. It builds each parent that needs no model call, up the tree, and adds
 329 // the first other parent to the queue.
 330 func (m *Memory) settle(key NodeKey) error {
 331         for {
 332                 parent := NodeKey{key.level + 1, key.index / 2}
 333                 ready, err := m.ready(parent)
 334                 if err != nil || !ready {
 335                         if err != nil {
 336                                 return fmt.Errorf("check parent readiness: %w", err)
 337                         }
 338
 339                         return nil
 340                 }
 341
 342                 left, right, err := m.children(parent)
 343                 if err != nil {
 344                         return fmt.Errorf("read parent children: %w", err)
 345                 }
 346
 347                 node, free := freeMerge(left, right)
 348                 if !free {
 349                         m.queue.AddMerge(parent)
 350
 351                         return nil
 352                 }
 353
 354                 err = m.tree.Add(node)
 355                 if err != nil {
 356                         return fmt.Errorf("add merged node: %w", err)
 357                 }
 358
 359                 key = parent
 360         }
 361 }
 362
 363 // addMessage builds the leaf of message when it needs no model call, or else
 364 // adds the leaf to the queue. Then it appends the leaf to the views. A crash
 365 // can stop an append after the leaf build and before the view save, so a leaf
 366 // that is built already stays as it is, and restoreQueue settles its parent.
 367 func (m *Memory) addMessage(message Message) error {
 368         built, err := m.tree.Built(0, message.ID)
 369         if err != nil {
 370                 return fmt.Errorf("check message leaf: %w", err)
 371         }
 372
 373         leaf, free := freeLeaf(message)
 374         switch {
 375         case built:
 376         case free:
 377                 err = m.build(leaf)
 378                 if err != nil {
 379                         return fmt.Errorf("build message leaf: %w", err)
 380                 }
 381         default:
 382                 m.queue.AddLeaf(message.ID)
 383         }
 384
 385         merged, err := m.chat.Append(m.tree)
 386         if err != nil {
 387                 return fmt.Errorf("append to chat view: %w", err)
 388         }
 389
 390         _, err = m.cview.Append(m.tree)
 391         if err == nil && merged {
 392                 err = m.cview.Coarsen(m.chat, m.tree)
 393         }
 394
 395         if err != nil {
 396                 return fmt.Errorf("append to compaction view: %w", err)
 397         }
 398
 399         return nil
 400 }
 401
 402 // save writes the views to view.json.
 403 func (m *Memory) save() error {
 404         data, err := json.Marshal(MemoryViewFile{
 405                 Chat:       m.chat.State(),
 406                 Compaction: m.cview.State(),
 407         })
 408         if err != nil {
 409                 return fmt.Errorf("encode view: %w", err)
 410         }
 411
 412         err = writeFileAtomic(m.viewPath(), append(data, '\n'))
 413         if err != nil {
 414                 return fmt.Errorf("save view: %w", err)
 415         }
 416
 417         return nil
 418 }
 419
 420 // task returns the build task of the node key, with its input read from the log
 421 // or the tree.
 422 func (m *Memory) task(key NodeKey) (Task, error) {
 423         task := Task{
 424                 Level:   key.level,
 425                 Index:   key.index,
 426                 Context: m.context(key.level, key.index),
 427         }
 428
 429         if key.level == 0 {
 430                 message, err := m.log.Message(key.index)
 431                 if err != nil {
 432                         return Task{}, fmt.Errorf("read leaf message: %w", err)
 433                 }
 434
 435                 task.Input = []string{leafSource(message)}
 436                 task.Images = imageFiles(message.Text)
 437
 438                 return task, nil
 439         }
 440
 441         left, right, err := m.children(key)
 442         if err != nil {
 443                 return Task{}, fmt.Errorf("read task children: %w", err)
 444         }
 445
 446         for _, child := range []Node{left, right} {
 447                 task.Input = append(task.Input, strings.ReplaceAll(child.Text, "\n", " "))
 448         }
 449
 450         return task, nil
 451 }
 452
 453 // failed logs the failed build of the node key with its cause err.
 454 func (m *Memory) failed(key NodeKey, err error) {
 455         m.logger.Warn("summary failed", "level", key.level, "index", key.index, "err", err)
 456 }
 457
 458 // run builds one node with the summarizer. A failed build stays in the queue
 459 // until the next message.
 460 func (m *Memory) run(key NodeKey, task Task) {
 461         defer m.workers.Done()
 462
 463         text, err := m.summarizer.Summarize(m.ctx, task)
 464
 465         m.mutex.Lock()
 466         defer m.mutex.Unlock()
 467
 468         if err == nil {
 469                 err = m.build(Node{
 470                         Level: key.level,
 471                         Index: key.index,
 472                         Text:  text,
 473                         Size:  len(text),
 474                 })
 475
 476                 m.syncer.Written()
 477         }
 478
 479         if err != nil && m.ctx.Err() == nil {
 480                 m.failed(key, err)
 481         }
 482
 483         if err != nil {
 484                 m.queue.Fail(key)
 485         } else {
 486                 m.queue.Done(key)
 487         }
 488
 489         close(m.changed)
 490
 491         m.changed = make(chan struct{})
 492         m.dispatch()
 493 }
 494
 495 // ready tells if both children of the node key are built and the node is not.
 496 func (m *Memory) ready(key NodeKey) (bool, error) {
 497         for _, index := range []int{2 * key.index, 2*key.index + 1} {
 498                 built, err := m.tree.Built(key.level-1, index)
 499                 if err != nil || !built {
 500                         if err != nil {
 501                                 return false, fmt.Errorf("check child readiness: %w", err)
 502                         }
 503
 504                         return false, nil
 505                 }
 506         }
 507
 508         built, err := m.tree.Built(key.level, key.index)
 509         if err != nil {
 510                 return !built, fmt.Errorf("check parent readiness: %w", err)
 511         }
 512
 513         return !built, nil
 514 }
 515
 516 // children reads the two children of the node key.
 517 func (m *Memory) children(key NodeKey) (Node, Node, error) {
 518         var children [2]Node
 519
 520         for n := range children {
 521                 child, built, err := m.tree.Node(key.level-1, 2*key.index+n)
 522                 if err != nil {
 523                         return Node{}, Node{}, fmt.Errorf("read child node: %w", err)
 524                 }
 525
 526                 if !built {
 527                         return Node{}, Node{}, fmt.Errorf("node (%d, %d) is not built", key.level-1, 2*key.index+n)
 528                 }
 529
 530                 children[n] = child
 531         }
 532
 533         return children[0], children[1], nil
 534 }
 535
 536 func (m *Memory) context(level, index int) string {
 537         end := index
 538         if level > 0 {
 539                 end = nodeEnd(level, index)
 540         }
 541
 542         return m.cview.Context(end)
 543 }
 544
 545 // Append logs a new message, adds it to the tree and the views, and starts the
 546 // builds that are ready, also the failed ones.
 547 func (m *Memory) Append(kind, text string) (Message, error) {
 548         return m.AppendDated(kind, text, "")
 549 }
 550
 551 // AppendDated appends a message with its RFC 3339 date and builds its nodes. An
 552 // empty date uses the clock, as Append does.
 553 func (m *Memory) AppendDated(kind, text, date string) (Message, error) {
 554         m.mutex.Lock()
 555         defer m.mutex.Unlock()
 556
 557         return m.appendDated(kind, text, date)
 558 }
 559
 560 // appendDated appends under the memory lock and updates the views and builds.
 561 func (m *Memory) appendDated(kind, text, date string) (Message, error) {
 562         message, err := m.log.AppendDated(kind, text, date)
 563         if err != nil {
 564                 return Message{}, fmt.Errorf("append dated log message: %w", err)
 565         }
 566
 567         defer m.syncer.Written()
 568
 569         err = m.addMessage(message)
 570         if err != nil {
 571                 return Message{}, fmt.Errorf("add dated message to memory: %w", err)
 572         }
 573
 574         err = m.save()
 575         if err != nil {
 576                 return Message{}, fmt.Errorf("save dated message view: %w", err)
 577         }
 578
 579         m.queue.Retry()
 580         m.dispatch()
 581
 582         return message, nil
 583 }
 584
 585 // AppendOnce appends a queued message. prepare saves its log ID before the
 586 // append, under the memory lock. A saved ID permits recovery after a stop
 587 // between that save and the append, without a second log entry. prepare must
 588 // not call Memory. The caller stops delivery after a failed append.
 589 func (m *Memory) AppendOnce(kind, text string, id *int, prepare func(int) error) (Message, error) {
 590         m.mutex.Lock()
 591         defer m.mutex.Unlock()
 592
 593         if id != nil && *id < m.log.Len() {
 594                 message, err := m.log.Message(*id)
 595                 if err != nil {
 596                         return Message{}, fmt.Errorf("read queued message: %w", err)
 597                 }
 598
 599                 if message.Kind != kind || message.Text != text {
 600                         return Message{}, errors.New("queued message does not match its log entry")
 601                 }
 602
 603                 return message, nil
 604         }
 605
 606         if id != nil && *id != m.log.Len() {
 607                 return Message{}, errors.New("queued message is beyond the log")
 608         }
 609
 610         err := prepare(m.log.Len())
 611         if err != nil {
 612                 return Message{}, fmt.Errorf("prepare queued message: %w", err)
 613         }
 614
 615         message, err := m.appendDated(kind, text, "")
 616         if err != nil {
 617                 return Message{}, fmt.Errorf("append queued message: %w", err)
 618         }
 619
 620         return message, nil
 621 }
 622
 623 // Wait returns when no build runs. The failed builds wait for the next message.
 624 func (m *Memory) Wait(ctx context.Context) error {
 625         for {
 626                 m.mutex.Lock()
 627
 628                 running := m.queue.Running()
 629                 changed := m.changed
 630                 m.mutex.Unlock()
 631
 632                 if running == 0 {
 633                         return nil
 634                 }
 635
 636                 select {
 637                 case <-changed:
 638                 case <-ctx.Done():
 639                         return ctx.Err()
 640                 }
 641         }
 642 }
 643
 644 // Settle returns when the chat view has no pending line, so that every message
 645 // so far is summarized. A pending line with no build that runs belongs to a
 646 // failed build, which waits for the next message, so Settle returns
 647 // errMemoryUnsettled in place of a wait that never ends.
 648 func (m *Memory) Settle(ctx context.Context) error {
 649         for {
 650                 m.mutex.Lock()
 651
 652                 pending := m.chat.Pending()
 653                 running := m.queue.Running()
 654                 changed := m.changed
 655                 m.mutex.Unlock()
 656
 657                 if !pending {
 658                         return nil
 659                 }
 660
 661                 if running == 0 {
 662                         return errMemoryUnsettled
 663                 }
 664
 665                 select {
 666                 case <-changed:
 667                 case <-ctx.Done():
 668                         return ctx.Err()
 669                 }
 670         }
 671 }
 672
 673 // Snapshot flushes all memory writes and runs snapshot while no append or
 674 // summary write can change the log, indexes, tree, or views. snapshot must not
 675 // call Memory.
 676 func (m *Memory) Snapshot(ctx context.Context, snapshot func() error) error {
 677         m.mutex.Lock()
 678         defer m.mutex.Unlock()
 679
 680         err := m.Flush(ctx)
 681         if err != nil {
 682                 return fmt.Errorf("flush memory snapshot: %w", err)
 683         }
 684
 685         err = snapshot()
 686         if err != nil {
 687                 return fmt.Errorf("copy memory snapshot: %w", err)
 688         }
 689
 690         return nil
 691 }
 692
 693 // Flush returns when every write before the call is durable.
 694 func (m *Memory) Flush(ctx context.Context) error {
 695         return m.syncer.Flush(ctx)
 696 }
 697
 698 // ViewLines returns the lines of the chat view, each with its newline, without
 699 // the leaf lines of the messages in skip.
 700 func (m *Memory) ViewLines(skip map[int]bool) []string {
 701         m.mutex.Lock()
 702         defer m.mutex.Unlock()
 703
 704         return m.chat.LinesWithout(skip)
 705 }
 706
 707 // Len returns the number of messages in the log.
 708 func (m *Memory) Len() int {
 709         m.mutex.Lock()
 710         defer m.mutex.Unlock()
 711
 712         return m.log.Len()
 713 }
 714
 715 // Message reads the message with the given ID.
 716 func (m *Memory) Message(id int) (Message, error) {
 717         m.mutex.Lock()
 718         defer m.mutex.Unlock()
 719
 720         return m.log.Message(id)
 721 }
 722
 723 // Node reads the node (l, i) if it is built.
 724 func (m *Memory) Node(level, index int) (Node, bool, error) {
 725         m.mutex.Lock()
 726         defer m.mutex.Unlock()
 727
 728         return m.tree.Node(level, index)
 729 }
 730
 731 // View returns the chat view as the model reads it.
 732 func (m *Memory) View() string {
 733         m.mutex.Lock()
 734         defer m.mutex.Unlock()
 735
 736         return m.chat.Render()
 737 }
 738
 739 // Context returns the compaction view for the build of node (l, i). It ends
 740 // before the message of a leaf, or after the last message of a merge, and it
 741 // stops at the first line that is not built.
 742 func (m *Memory) Context(level, index int) string {
 743         m.mutex.Lock()
 744         defer m.mutex.Unlock()
 745
 746         return m.context(level, index)
 747 }
 748
 749 // rebuildComplete checks the whole tree, not only the visible view. A compactor
 750 // can fail without an HTTP error, for example with an empty line. Such a failed
 751 // merge can be absent from the view and must prevent a swap.
 752 func (m *Memory) rebuildComplete() error {
 753         m.mutex.Lock()
 754         defer m.mutex.Unlock()
 755
 756         if len(m.queue.leaves) != 0 || len(m.queue.queued) != 0 {
 757                 return errors.New("rebuild failed: summary tree has unfinished nodes")
 758         }
 759
 760         return nil
 761 }
 762
 763 // buildModelLines returns the sizes of the nodes that the model wrote, in tree
 764 // order. A node that fits its source with no model call is not one of them.
 765 func (m *Memory) buildModelLines() ([]int, error) {
 766         m.mutex.Lock()
 767         defer m.mutex.Unlock()
 768
 769         keys, err := m.tree.Keys()
 770         if err != nil {
 771                 return nil, fmt.Errorf("list built nodes: %w", err)
 772         }
 773
 774         var sizes []int
 775
 776         for _, key := range keys {
 777                 var node Node
 778
 779                 node, _, err = m.tree.Node(key.level, key.index)
 780                 if err != nil {
 781                         return nil, fmt.Errorf("read built node: %w", err)
 782                 }
 783
 784                 var model bool
 785
 786                 model, err = m.buildBuiltByModel(key)
 787                 if err != nil {
 788                         return nil, fmt.Errorf("check model source: %w", err)
 789                 }
 790
 791                 if model {
 792                         sizes = append(sizes, node.Size)
 793                 }
 794         }
 795
 796         return sizes, nil
 797 }
 798
 799 // buildBuiltByModel tells if the node key needed a model call: a leaf whose
 800 // source is over nodeBytes, or a merge whose children do not fit in one node.
 801 func (m *Memory) buildBuiltByModel(key NodeKey) (bool, error) {
 802         if key.level == 0 {
 803                 message, err := m.log.Message(key.index)
 804                 if err != nil {
 805                         return false, fmt.Errorf("read leaf source: %w", err)
 806                 }
 807
 808                 _, free := freeLeaf(message)
 809
 810                 return !free, nil
 811         }
 812
 813         left, right, err := m.children(key)
 814         if err != nil {
 815                 return false, fmt.Errorf("read merge sources: %w", err)
 816         }
 817
 818         _, free := freeMerge(left, right)
 819
 820         return !free, nil
 821 }