**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 :)

else if (name == DEFAULT_WAL_FILE_NAME)
                    rotate(lock);
                break;
            }
            throw;
        }
        if (action_type == ActionType::ADD_PART)
        {
            MergedBlockOutputStream part_out(
                part,
                data_part_storage_builder,
                metadata_snapshot,
                block.getNamesAndTypesList(),
                {},
                CompressionCodecFactory::instance().get("NONE", {}),
                NO_TRANSACTION_PTR);
            part->minmax_idx->update(block, storage.getMinMaxColumnsNames(metadata_snapshot->getPartitionKey()));
            part->partition.create(metadata_snapshot, block, 0, context);
            part->setColumns(block.getNamesAndTypesList(), {});
            if (metadata_snapshot->hasSortingKey())
                metadata_snapshot->getSortingKey().expression->execute(block);
            part_out.write(block);
            for (const auto & projection : metadata_snapshot->getProjections())
            {
                auto projection_block = projection.calculate(block, context);
                auto temp_part = MergeTreeDataWriter::writeInMemoryProjectionPart(storage, log, projection_block, projection, data_part_storage_builder, part.get());
                temp_part.finalize();
                if (projection_block.rows())
                    part->addProjectionPart(projection.name, std::move(temp_part.part));
            }