**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 :)

}
        if (!part->index_granularity_info.is_adaptive)
            has_non_adaptive_parts.store(true, std::memory_order_relaxed);
        else
            has_adaptive_parts.store(true, std::memory_order_relaxed);
        
        if (part->hasLightweightDelete())
            has_lightweight_in_parts.store(true, std::memory_order_relaxed);
        part->modification_time = part_disk_ptr->getLastModified(fs::path(relative_data_path) / part_name).epochTime();
        
        part->setState(DataPartState::Active);
        std::lock_guard loading_lock(mutex);
        auto [it, inserted] = data_parts_indexes.insert(part);
        
        if (!inserted)
        {
            if ((*it)->checksums.getTotalChecksumHex() == part->checksums.getTotalChecksumHex())
            {
                LOG_ERROR(log, "Remove duplicate part {}", data_part_storage->getFullPath());
                duplicate_parts_to_remove.push_back(part);
            }
            else
                throw Exception("Part " + part->name + " already exists but with different checksums", ErrorCodes::DUPLICATE_DATA_PART);
        }
        addPartContributionToDataVolume(part);
    };
    std::mutex part_select_mutex;
    try
    {
        for (size_t thread = 0; thread < num_threads; ++thread)