**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 :)

{
    removePartsInRangeFromWorkingSetAndGetPartsToRemoveFromZooKeeper(txn, drop_range, lock);
}
MergeTreeData::DataPartsVector MergeTreeData::removePartsInRangeFromWorkingSetAndGetPartsToRemoveFromZooKeeper(
        MergeTreeTransaction * txn, const MergeTreePartInfo & drop_range, DataPartsLock & lock)
{
    DataPartsVector parts_to_remove;
    if (drop_range.min_block > drop_range.max_block)
        throw Exception(ErrorCodes::LOGICAL_ERROR, "Invalid drop range: {}", drop_range.getPartName());
    auto partition_range = getVisibleDataPartsVectorInPartition(txn, drop_range.partition_id, &lock);
    for (const DataPartPtr & part : partition_range)
    {
        if (part->info.partition_id != drop_range.partition_id)
            throw Exception("Unexpected partition_id of part " + part->name + ". This is a bug.", ErrorCodes::LOGICAL_ERROR);
        
        bool is_drop_part = !drop_range.isFakeDropRangePart() && drop_range.min_block;
        if (is_drop_part && (part->info.min_block != drop_range.min_block || part->info.max_block != drop_range.max_block || part->info.getMutationVersion() != drop_range.getMutationVersion()))
        {