**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 :)

{
    auto policy = getStoragePolicy();
    if (ttl.destination_type == DataDestinationType::VOLUME)
    {
        for (const auto & disk : policy->getVolumeByName(ttl.destination_name)->getDisks())
            if (disk->getName() == part.data_part_storage->getDiskName())
                return true;
    }
    else if (ttl.destination_type == DataDestinationType::DISK)
        return policy->getDiskByName(ttl.destination_name)->getName() == part.data_part_storage->getDiskName();
    return false;
}
CompressionCodecPtr MergeTreeData::getCompressionCodecForPart(size_t part_size_compressed, const IMergeTreeDataPart::TTLInfos & ttl_infos, time_t current_time) const
{
    auto metadata_snapshot = getInMemoryMetadataPtr();
    const auto & recompression_ttl_entries = metadata_snapshot->getRecompressionTTLs();
    auto best_ttl_entry = selectTTLDescriptionForTTLInfos(recompression_ttl_entries, ttl_infos.recompression_ttl, current_time, true);
    if (best_ttl_entry)
        return CompressionCodecFactory::instance().get(best_ttl_entry->recompression_codec, {});
    return getContext()->chooseCompressionCodec(
        part_size_compressed,
        static_cast<double>(part_size_compressed) / getTotalActiveSizeInBytes());
}
MergeTreeData::DataParts MergeTreeData::getDataParts(const DataPartStates & affordable_states) const