Describe the unexpected behaviour
I'd expect GlobalThreadPool to expose all params outside to the configuration, so that they can be tweaked.

Here's the code:
https://github.com/ClickHouse/ClickHouse/blob/master/src/Common/ThreadPool.cpp#L323-L334

void GlobalThreadPool::initialize(size_t max_threads)
{
    if (the_instance)
    {
        throw DB::Exception(DB::ErrorCodes::LOGICAL_ERROR,
            "The global thread pool is initialized twice");
    }

    the_instance.reset(new GlobalThreadPool(max_threads,
        1000 /*max_free_threads*/, 10000 /*max_queue_size*/,
        false /*shutdown_on_exception*/));
}

I'd expect both max_free_threads and max_queue_size to be configurable via settings.xml, similar to max_threads.

Is this expansion planned? The possibility of increasing max_queue_size would allow us to manage table attaching in a much more direct, faster way.