r := results{}
	g := new(errgroup.Group)
	f := &worker.Fetcher{
		ProxyClient:  proxyClient,
		SourceClient: sourceClient,
		DB:           postgres.New(db),
	}
	for path, vers := range versionsByPath {
		path := path
		vers := vers
		// Process versions of the same module sequentially, to avoid DB contention.
		g.Go(func() error {
			for _, v := range vers {
				if err := fetch(ctx, db, f, path, v, &r); err != nil {
					return err
				}
			}
			return nil
		})
	}
	if err := g.Wait(); err != nil {
		return err
	}
	log.Infof(ctx, "Successfully fetched all modules: %v", time.Since(start))

	r := results{}
	var (
		mu     sync.Mutex
		errors []error
	)
	g := new(errgroup.Group)
	f := &worker.Fetcher{
		ProxyClient:  proxyClient,
		SourceClient: sourceClient,
		DB:           postgres.New(db),
	}
	for path, vers := range versionsByPath {
		path := path
		vers := vers
		// Process versions of the same module sequentially, to avoid DB contention.
		g.Go(func() error {
			for _, v := range vers {
				if err := fetch(ctx, db, f, path, v, &r); err != nil {
					if *keep_going {
						mu.Lock()
						errors = append(errors, err)
						mu.Unlock()
						continue
					}
					return err
				}
			}
			return nil
		})
	}
	if err := g.Wait(); err != nil {
		return err
	}
	if len(errors) != 0 {
		return multierror.New(errors)
	}
	log.Infof(ctx, "Successfully fetched all modules: %v", time.Since(start))