**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 :)

{
    std::unordered_set<String> partition_ids;
    for (const auto & ast : asts)
        partition_ids.emplace(getPartitionIDFromQuery(ast, local_context));
    return partition_ids;
}
std::set<String> MergeTreeData::getPartitionIdsAffectedByCommands(
    const MutationCommands & commands, ContextPtr query_context) const
{
    std::set<String> affected_partition_ids;
    for (const auto & command : commands)
    {
        if (!command.partition)
        {
            affected_partition_ids.clear();
            break;
        }
        affected_partition_ids.insert(
            getPartitionIDFromQuery(command.partition, query_context)
        );
    }
    return affected_partition_ids;
}
MergeTreeData::DataPartsVector MergeTreeData::getDataPartsVectorForInternalUsage(