**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 :)

{
    bool prefixed = false;
    String id;
    if (format_version < MERGE_TREE_DATA_MIN_FORMAT_VERSION_WITH_CUSTOM_PARTITIONING)
    {
        /
        if (const auto * partition_lit = partition_ast->as<ASTPartition &>().value->as<ASTLiteral>())
        {
            id = partition_lit->value.getType() == Field::Types::UInt64
                 ? toString(partition_lit->value.get<UInt64>())
                 : partition_lit->value.safeGet<String>();
            prefixed = true;
        }
        else
            id = getPartitionIDFromQuery(partition_ast, local_context);
    }
    else
        id = getPartitionIDFromQuery(partition_ast, local_context);
    return [prefixed, id](const String & partition_id)
    {
        if (prefixed)
            return startsWith(partition_id, id);
        else
            return id == partition_id;
    };
}
PartitionCommandsResultInfo MergeTreeData::freezePartition(