Ordinary database engine is deprecated but there is no simple mean to change database engine to Atomic for existing databases.

Possible options:
- ALTER DATABASE MODIFY ENGINE query.
- Flag that triggers migration at ClickHouse startup.

The latter should be easier to implement. 

ReplicatedMergeTreeLogEntryData entry;
        {
            auto src_table_id = src_data.getStorageID();
            entry.type = ReplicatedMergeTreeLogEntryData::REPLACE_RANGE;
            entry.source_replica = replica_name;
            entry.create_time = time(nullptr);
            entry.replace_range_entry = std::make_shared<ReplicatedMergeTreeLogEntryData::ReplaceRangeEntry>();
            auto & entry_replace = *entry.replace_range_entry;
            entry_replace.drop_range_part_name = drop_range_fake_part_name;
            entry_replace.from_database = src_table_id.database_name;
            entry_replace.from_table = src_table_id.table_name;
            for (const auto & part : src_parts)
                entry_replace.src_part_names.emplace_back(part->name);
            for (const auto & part : dst_parts)
                entry_replace.new_part_names.emplace_back(part->name);
            for (const String & checksum : part_checksums)
                entry_replace.part_names_checksums.emplace_back(checksum);
            entry_replace.columns_version = -1;
        }
        
        if (replace)
            clearBlocksInPartition(*zookeeper, drop_range.partition_id, drop_range.max_block, drop_range.max_block);
        DataPartsVector parts_to_remove;
        Coordination::Responses op_results;
        try
        {
            Coordination::Requests ops;
            for (size_t i = 0; i < dst_parts.size(); ++i)
            {
                getCommitPartOps(ops, dst_parts[i], block_id_paths[i]);