**Describe the bug**

Since we upgraded to 20.10.3.30, one of our clickhouse cluster takes much more time to start. (Up to 50 minutes, and before it took ~3 minutes)
The log file is filled with
>  <Debug> DiskLocal: Reserving 1.00 MiB on disk `default`, having unreserved 16.90 TiB

Additionally, the memory consumption increases, linearly, a lot (up to arround 230 G for us) and then drop back to normal values once clickhouse finished starting up. During that loading phase, a single CPU core is used at 100%.
If that memory is not available for the machine, clickhouse gets OOMed by the kernel.


**How to reproduce**
* Issue appeared after we upgraded to ClickHouse server version 20.10.3.30

* How could I find wich of our tables may be responsible for that ?


**Expected behavior**
A fast startup :)

{
    
    std::unique_lock lock(clear_old_temporary_directories_mutex, std::defer_lock);
    if (!lock.try_lock())
        return 0;
    const auto settings = getSettings();
    time_t current_time = time(nullptr);
    ssize_t deadline = current_time - custom_directories_lifetime_seconds;
    size_t cleared_count = 0;
    
    for (const auto & disk : getDisks())
    {
        if (disk->isBroken())
            continue;
        for (auto it = disk->iterateDirectory(relative_data_path); it->isValid(); it->next())
        {
            const std::string & basename = it->name();
            bool start_with_valid_prefix = false;
            for (const auto & prefix : valid_prefixes)
            {
                if (startsWith(basename, prefix))
                {