**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 new_table_path_parent = parentPath(new_table_path);
        disk->createDirectories(new_table_path_parent);
        disk->moveDirectory(relative_data_path, new_table_path);
    }
    if (!getStorageID().hasUUID())
        getContext()->dropCaches();
    for (const auto & part : data_parts_by_info)
        part->data_part_storage->changeRootPath(relative_data_path, new_table_path);
    relative_data_path = new_table_path;
    renameInMemory(new_table_id);
}
void MergeTreeData::renameInMemory(const StorageID & new_table_id)
{
    IStorage::renameInMemory(new_table_id);
    std::atomic_store(&log_name, std::make_shared<String>(new_table_id.getNameForLogs()));
    log = &Poco::Logger::get(*log_name);
}
void MergeTreeData::dropAllData()
{
    LOG_TRACE(log, "dropAllData: waiting for locks.");
    auto lock = lockParts();
    LOG_TRACE(log, "dropAllData: removing data from memory.");
    DataPartsVector all_parts(data_parts_by_info.begin(), data_parts_by_info.end());
    data_parts_indexes.clear();
    column_sizes.clear();
    {
        std::lock_guard wal_lock(write_ahead_log_mutex);
        if (write_ahead_log)
            write_ahead_log->shutdown();
    }