**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 :)

{
    DataPartsVector parts_to_remove;
    const auto * partition_ast = partition->as<ASTPartition>();
    if (partition_ast && partition_ast->all)
        parts_to_remove = getVisibleDataPartsVector(local_context);
    else
    {
        const String partition_id = getPartitionIDFromQuery(partition, local_context);
        parts_to_remove = getVisibleDataPartsVectorInPartition(local_context, partition_id);
    }
    UInt64 partition_size = 0;
    for (const auto & part : parts_to_remove)
        partition_size += part->getBytesOnDisk();
    auto table_id = getStorageID();
    getContext()->checkPartitionCanBeDropped(table_id.database_name, table_id.table_name, partition_size);
}
void MergeTreeData::checkPartCanBeDropped(const String & part_name)
{
    auto part = getPartIfExists(part_name, {MergeTreeDataPartState::Active});
    if (!part)
        throw Exception(ErrorCodes::NO_SUCH_DATA_PART, "No part {} in committed state", part_name);
    auto table_id = getStorageID();
    getContext()->checkPartitionCanBeDropped(table_id.database_name, table_id.table_name, part->getBytesOnDisk());
}
void MergeTreeData::movePartitionToDisk(const ASTPtr & partition, const String & name, bool moving_part, ContextPtr local_context)
{
    String partition_id;
    if (moving_part)
        partition_id = partition->as<ASTLiteral &>().value.safeGet<String>();