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. 

{
        std::lock_guard lock{mutex};
        return database_name;
    }
    
    virtual UUID getUUID() const { return UUIDHelpers::Nil; }
    virtual void renameDatabase(ContextPtr, const String & )
    {
        throw Exception(getEngineName() + ": RENAME DATABASE is not supported", ErrorCodes::NOT_IMPLEMENTED);
    }
    
    virtual String getDataPath() const { return {}; }
    
    virtual String getTableDataPath(const String & ) const { return {}; }
    
    virtual String getTableDataPath(const ASTCreateQuery & ) const { return {}; }
    
    virtual String getMetadataPath() const { return {}; }
    
    virtual String getObjectMetadataPath(const String & ) const { return {}; }
    
    virtual bool shouldBeEmptyOnDetach() const { return true; }
    virtual void assertCanBeDetached(bool ) {}
    virtual void waitDetachedTableNotInUse(const UUID & ) { }
    virtual void checkDetachedTableNotInUse(const UUID & ) { }
    
    virtual void shutdown() = 0;
    
    virtual void drop(ContextPtr ) {}
    virtual void applySettingsChanges(const SettingsChanges &, ContextPtr)