If they are defined, they can override table-level settings.
{
    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
{
    DataParts res;
    {
        auto lock = lockParts();
        for (auto state : affordable_states)
        {
            auto range = getDataPartsStateRange(state);
            res.insert(range.begin(), range.end());
        }
    }
    return res;
}
MergeTreeData::DataParts MergeTreeData::getDataPartsForInternalUsage() const
{
    return getDataParts({DataPartState::Active});
}
MergeTreeData::DataPartsVector MergeTreeData::getDataPartsVectorForInternalUsage() const