**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 :)

const StoragePtr & source_table, const StorageMetadataPtr & src_snapshot, const StorageMetadataPtr & my_snapshot) const
{
    return checkStructureAndGetMergeTreeData(*source_table, src_snapshot, my_snapshot);
}
std::pair<MergeTreeData::MutableDataPartPtr, scope_guard> MergeTreeData::cloneAndLoadDataPartOnSameDisk(
    const MergeTreeData::DataPartPtr & src_part,
    const String & tmp_part_prefix,
    const MergeTreePartInfo & dst_part_info,
    const StorageMetadataPtr & metadata_snapshot,
    const MergeTreeTransactionPtr & txn,
    HardlinkedFiles * hardlinked_files,
    bool copy_instead_of_hardlink)
{
    /
    bool does_storage_policy_allow_same_disk = false;
    for (const DiskPtr & disk : getStoragePolicy()->getDisks())
    {
        if (disk->getName() == src_part->data_part_storage->getDiskName())
        {
            does_storage_policy_allow_same_disk = true;
            break;
        }
    }
    if (!does_storage_policy_allow_same_disk)
        throw Exception(
            ErrorCodes::BAD_ARGUMENTS,
            "Could not clone and load part {} because disk does not belong to storage policy",
            quoteString(src_part->data_part_storage->getFullPath()));
    String dst_part_name = src_part->getNewName(dst_part_info);