**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 :)

ContextPtr query_context, const StorageSnapshotPtr & storage_snapshot, SelectQueryInfo & query_info) const
{
    const auto & metadata_snapshot = storage_snapshot->metadata;
    const auto & settings = query_context->getSettingsRef();
    if (!settings.allow_experimental_projection_optimization || query_info.ignore_projections || query_info.is_projection_query)
        return std::nullopt;
    /
    if (settings.parallel_replicas_count > 1 || settings.max_parallel_replicas > 1)
        return std::nullopt;
    auto query_ptr = query_info.original_query;
    auto * select_query = query_ptr->as<ASTSelectQuery>();
    if (!select_query)
        return std::nullopt;
    /
    if (select_query->final())
        return std::nullopt;
    /
    if (select_query->sampleSize())
        return std::nullopt;
    /
    if (settings.allow_experimental_query_deduplication)
        return std::nullopt;
    /
    if (select_query->arrayJoinExpressionList().first)
        return std::nullopt;
    /