And waits for them. That's pointless.
{
    if (fetcher.blocker.isCancelled())
    {
        disable_reason = fmt::format("Not executing fetch of part {} because replicated fetches are cancelled now.", entry.new_part_name);
        return false;
    }
    size_t busy_threads_in_pool = CurrentMetrics::values[CurrentMetrics::BackgroundFetchesPoolTask].load(std::memory_order_relaxed);
    if (busy_threads_in_pool >= replicated_fetches_pool_size)
    {
        disable_reason = fmt::format("Not executing fetch of part {} because {} fetches already executing, max {}.", entry.new_part_name, busy_threads_in_pool, replicated_fetches_pool_size);
        return false;
    }
    if (replicated_fetches_throttler->isThrottling())
    {
        disable_reason = fmt::format("Not executing fetch of part {} because fetches have already throttled by network settings "
                                     "<max_replicated_fetches_network_bandwidth> or <max_replicated_fetches_network_bandwidth_for_server>.", entry.new_part_name);
        return false;
    }
    return true;
}
bool StorageReplicatedMergeTree::partIsAssignedToBackgroundOperation(const DataPartPtr & part) const
{
    return queue.isVirtualPart(part);
}
void StorageReplicatedMergeTree::mergeSelectingTask()