**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::optional<ProjectionCandidate> minmax_count_projection_candidate;
    if (!candidates.empty())
    {
        minmax_count_projection_candidate.emplace(std::move(candidates.front()));
        candidates.clear();
    }
    MergeTreeDataSelectExecutor reader(*this);
    std::shared_ptr<PartitionIdToMaxBlock> max_added_blocks;
    if (settings.select_sequential_consistency)
    {
        if (const StorageReplicatedMergeTree * replicated = dynamic_cast<const StorageReplicatedMergeTree *>(this))
            max_added_blocks = std::make_shared<PartitionIdToMaxBlock>(replicated->getMaxAddedBlocks());
    }
    const auto & snapshot_data = assert_cast<const MergeTreeData::SnapshotData &>(*storage_snapshot->data);
    const auto & parts = snapshot_data.parts;
    auto prepare_min_max_count_projection = [&]()
    {
        DataPartsVector normal_parts;
        query_info.minmax_count_projection_block = getMinMaxCountProjectionBlock(
            metadata_snapshot,
            minmax_count_projection_candidate->required_columns,
            !query_info.filter_asts.empty() || analysis_result.prewhere_info || analysis_result.before_where,
            query_info,
            parts,
            normal_parts,
            max_added_blocks.get(),
            query_context);
        /
        if (!query_info.minmax_count_projection_block)
            return;