**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 :)

{
    total_active_size_bytes.fetch_add(bytes, std::memory_order_acq_rel);
    total_active_size_rows.fetch_add(rows, std::memory_order_acq_rel);
    total_active_size_parts.fetch_add(parts, std::memory_order_acq_rel);
}
void MergeTreeData::setDataVolume(size_t bytes, size_t rows, size_t parts)
{
    total_active_size_bytes.store(bytes, std::memory_order_release);
    total_active_size_rows.store(rows, std::memory_order_release);
    total_active_size_parts.store(parts, std::memory_order_release);
}
bool MergeTreeData::insertQueryIdOrThrow(const String & query_id, size_t max_queries) const
{
    std::lock_guard lock(query_id_set_mutex);
    return insertQueryIdOrThrowNoLock(query_id, max_queries);
}
bool MergeTreeData::insertQueryIdOrThrowNoLock(const String & query_id, size_t max_queries) const
{
    if (query_id_set.find(query_id) != query_id_set.end())
        return false;
    if (query_id_set.size() >= max_queries)
        throw Exception(
            ErrorCodes::TOO_MANY_SIMULTANEOUS_QUERIES,
            "Too many simultaneous queries for table {}. Maximum is: {}",
            *std::atomic_load(&log_name),
            max_queries);
    query_id_set.insert(query_id);
    return true;
}
void MergeTreeData::removeQueryId(const String & query_id) const