**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 :)

{
    DataPartPtr part_to_delete;
    {
        auto lock = lockParts();
        auto part_name_with_state = part->getNameWithState();
        LOG_TRACE(log, "Trying to immediately remove part {}", part_name_with_state);
        if (part->getState() != DataPartState::Temporary)
        {
            auto it = data_parts_by_info.find(part->info);
            if (it == data_parts_by_info.end() || (*it).get() != part.get())
                throw Exception("Part " + part->name + " doesn't exist", ErrorCodes::LOGICAL_ERROR);
            part.reset();
            if (!((*it)->getState() == DataPartState::Outdated && it->unique()))
            {
                if ((*it)->getState() != DataPartState::Outdated)
                    LOG_WARNING(log, "Cannot immediately remove part {} because it's not in Outdated state "
                             "usage counter {}", part_name_with_state, it->use_count());