presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/backup/BackupManager.java/BackupManager/submit
class BackupManager:    public CompletableFuture<?> submit(UUID uuid, File source)
    {
        requireNonNull(uuid, "uuid is null");
        requireNonNull(source, "source is null");

        if (!backupStore.isPresent()) {
            return completedFuture(null);
        }

        // TODO: decrement when the running task is finished (not immediately on cancel)
        pendingBackups.incrementAndGet();
        CompletableFuture<?> future = runAsync(new BackgroundBackup(uuid, source), executorService);
        future.whenComplete((none, throwable) -> pendingBackups.decrementAndGet());
        return future;
    }