**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 :)

{
    auto lock = lockParts();
    auto it = data_parts_by_info.find(part_info);
    if (it == data_parts_by_info.end())
        return nullptr;
    for (auto state : valid_states)
        if ((*it)->getState() == state)
            return *it;
    return nullptr;
}
MergeTreeData::DataPartPtr MergeTreeData::getPartIfExists(const String & part_name, const MergeTreeData::DataPartStates & valid_states)
{
    return getPartIfExists(MergeTreePartInfo::fromPartName(part_name, format_version), valid_states);
}
static void loadPartAndFixMetadataImpl(MergeTreeData::MutableDataPartPtr part)
{
    part->loadColumnsChecksumsIndexes(false, true);
    part->modification_time = part->data_part_storage->getLastModified().epochTime();
    part->data_part_storage->removeDeleteOnDestroyMarker();
    part->data_part_storage->removeVersionMetadata();
}
void MergeTreeData::calculateColumnAndSecondaryIndexSizesImpl()