What causes "failed to get subtasks for task %d: %w" in vxcontrol/pentagi?

Restore PostgreSQL connectivity and retry LoadSubtasks (flows are resumable — nothing is lost).

failed to get subtasks for task %d: %w

Error message

failed to get subtasks for task %d: %w

What it means

Wraps the error from DB.GetTaskSubtasks when loading all persisted subtask workers for a task into the subtaskController. Failure means the in-memory flow workers could not be restored — usually a database connectivity/query error. The taskID is included to help locate the offending task.

Source

Thrown at backend/pkg/controller/subtasks.go:48

	taskCtx  *TaskContext
	subtasks map[int64]SubtaskWorker
}

func NewSubtaskController(taskCtx *TaskContext) SubtaskController {
	return &subtaskController{
		mx:       &sync.Mutex{},
		taskCtx:  taskCtx,
		subtasks: make(map[int64]SubtaskWorker),
	}
}

func (stc *subtaskController) LoadSubtasks(ctx context.Context, taskID int64, updater TaskUpdater) error {
	stc.mx.Lock()
	defer stc.mx.Unlock()

	subtasks, err := stc.taskCtx.DB.GetTaskSubtasks(ctx, taskID)
	if err != nil {
		return fmt.Errorf("failed to get subtasks for task %d: %w", taskID, err)
	}

	if len(subtasks) == 0 {
		return fmt.Errorf("no subtasks found for task %d: %w", taskID, ErrNothingToLoad)
	}

	for _, subtask := range subtasks {
		st, err := LoadSubtaskWorker(ctx, subtask, stc.taskCtx, updater)
		if err != nil {
			if errors.Is(err, ErrNothingToLoad) {
				continue
			}

			return fmt.Errorf("failed to create subtask worker: %w", err)
		}

		stc.subtasks[subtask.ID] = st
	}

View on GitHub (pinned to ea665308ba)

Solutions

Restore PostgreSQL connectivity and retry LoadSubtasks (flows are resumable — nothing is lost).
Check the wrapped error for SQLSTATE/context errors; if context.Canceled, the caller canceled too early.
Verify migrations ran (goose) — an outdated subtasks schema breaks GetTaskSubtasks.
Confirm the taskID is valid and the task row still exists at load time.

Example fix

// before: retrying immediately in a tight loop
for {
    if err := stc.LoadSubtasks(ctx, taskID, updater); err == nil { break }
}
// after: backoff + root-cause log
if err := stc.LoadSubtasks(ctx, taskID, updater); err != nil {
    logrus.WithError(err).WithField("task_id", taskID).Error("load failed")
    time.Sleep(backoff)
    return
}

Defensive patterns

Strategy: retry

Validate before calling

if err := db.PingContext(ctx); err != nil {
    return fmt.Errorf("database unreachable, cannot load task %d", taskID)
}
// taskID must be positive
if taskID <= 0 { return ErrInvalidTaskID }

Type guard

func isDBError(err error) bool {
    var pgErr *pgconn.PgError
    return errors.As(err, &pgErr) || errors.Is(err, context.Canceled)
}

Try / catch

err := stc.LoadSubtasks(ctx, taskID, updater)
if err != nil {
    if isDBError(err) {
        // transient: backoff and retry
        time.Sleep(2 * time.Second)
        return stc.LoadSubtasks(ctx, taskID, updater)
    }
    return err
}

Prevention

Verify DB health (ping/migrations) at startup before accepting flow-resume requests.
Run all goose migrations before the server starts serving.
Wrap DB reads in retry with backoff for transient connection errors.
Log the wrapped root error with taskID for fast diagnosis.

When it happens

Trigger: subtaskController.LoadSubtasks(ctx, taskID, updater) calls stc.taskCtx.DB.GetTaskSubtasks(ctx, taskID) and the SQLC query returns an error — connection failure, canceled context, or a schema mismatch.

Common situations: Postgres down or restarting when a server restart tries to resume flows; pgvector/DB migration not applied so the subtasks query fails; taskID referencing a task deleted concurrently between existence check and load; network partition between backend and DB.

Understand the failure class

Background: Database query failed: Internal Server Error 500s wrapping SQL, Prisma, and connection failures — what to check first — this error's family across 16 libraries.

Related errors

AI-assisted analysis of vxcontrol/pentagi@ea665308ba (2026-09-01). Data as JSON: /api/errors/5943ac3f4f2c2651. Report an issue: GitHub.