**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 (mrk_ext == getNonAdaptiveMrkExtension())
        return MergeTreeDataPartType::Wide;
    if (mrk_ext == getAdaptiveMrkExtension(MergeTreeDataPartType::Wide))
        return MergeTreeDataPartType::Wide;
    if (mrk_ext == getAdaptiveMrkExtension(MergeTreeDataPartType::Compact))
        return MergeTreeDataPartType::Compact;
    throw Exception("Can't determine part type, because of unknown mark extension " + mrk_ext, ErrorCodes::UNKNOWN_PART_TYPE);
}
MergeTreeData::MutableDataPartPtr MergeTreeData::createPart(
    const String & name, const DataPartStoragePtr & data_part_storage, const IMergeTreeDataPart * parent_part) const
{
    return createPart(name, MergeTreePartInfo::fromPartName(name, format_version), data_part_storage, parent_part);
}
MergeTreeData::MutableDataPartPtr MergeTreeData::createPart(
    const String & name, const MergeTreePartInfo & part_info,
    const DataPartStoragePtr & data_part_storage, const IMergeTreeDataPart * parent_part) const
{
    MergeTreeDataPartType type;
    auto mrk_ext = MergeTreeIndexGranularityInfo::getMarksExtensionFromFilesystem(data_part_storage);
    if (mrk_ext)
        type = getPartTypeFromMarkExtension(*mrk_ext);
    else
    {
        
        type = choosePartTypeOnDisk(0, 0);
    }
    return createPart(name, type, part_info, data_part_storage, parent_part);
}
void MergeTreeData::changeSettings(