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. 

{
        return static_cast<time_t>(0);
    }
    
    ASTPtr tryGetCreateTableQuery(const String & name, ContextPtr context) const noexcept
    {
        return getCreateTableQueryImpl(name, context, false);
    }
    ASTPtr getCreateTableQuery(const String & name, ContextPtr context) const
    {
        return getCreateTableQueryImpl(name, context, true);
    }
    
    virtual ASTPtr getCreateDatabaseQuery() const = 0;
    String getDatabaseComment() const
    {
        std::lock_guard lock{mutex};
        return comment;
    }
    void setDatabaseComment(String new_comment)
    {
        std::lock_guard lock{mutex};
        comment = std::move(new_comment);
    }
    
    String getDatabaseName() const