**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 :)

}
    /
    TransactionID tid = txn ? txn->tid : Tx::PrehistoricTID;
    dst_data_part->version.setCreationTID(tid, nullptr);
    dst_data_part->storeVersionMetadata();
    dst_data_part->is_temp = true;
    dst_data_part->loadColumnsChecksumsIndexes(require_part_metadata, true);
    dst_data_part->modification_time = dst_part_storage->getLastModified().epochTime();
    return std::make_pair(dst_data_part, std::move(temporary_directory_lock));
}
String MergeTreeData::getFullPathOnDisk(const DiskPtr & disk) const
{
    return disk->getPath() + relative_data_path;
}
DiskPtr MergeTreeData::tryGetDiskForDetachedPart(const String & part_name) const
{
    String additional_path = "detached/";
    const auto disks = getStoragePolicy()->getDisks();
    for (const DiskPtr & disk : disks)
        if (disk->exists(relative_data_path + additional_path + part_name))
            return disk;
    return nullptr;
}
DiskPtr MergeTreeData::getDiskForDetachedPart(const String & part_name) const
{
    if (auto disk = tryGetDiskForDetachedPart(part_name))
        return disk;
    throw DB::Exception(ErrorCodes::BAD_DATA_PART_NAME, "Detached part \"{}\" not found", part_name);
}
Strings MergeTreeData::getDataPaths() const