Event driven server that wastes CPU when threaded doesn't

[Nick Vatamaniuc]

Good point. enterprise.adbapi is designed to solve the problem. The
other interface was deprecated.

Thanks,
Nick Vatamaniuc


Jean-Paul Calderone wrote:
> On 29 Oct 2006 13:13:32 -0800, Nick Vatamaniuc <vatamane at gmail.com> wrote:
> >Snor wrote:
> >> I'm attempting to create a lobby & game server for a multiplayer game,
> >> and have hit a problem early on with the server design. I am stuck
> >> between using a threaded server, and using an event driven server. I've
> >> been told time and time again that I should use an event driven server
> >> design (that is, use twisted).
> >>
> >> There is a lot of interaction between the clients and they would often
> >> need to write to the same list of values, which of course becomes a
> >> problem with a threaded server - so event driven solves that problem,
> >> and I assumed it would solve all my problems. However some requests
> >> from clients would require that the server goes on to query a mySQL
> >> server (separate machine from the server). As this occurs, there is a
> >> small amount of lag while the communication with the mySQL server takes
> >> place, and there could be another 100 clients waiting to make a request
> >> at this point, meanwhile the server is idling while waiting for a
> >> response from the mySQL server - obviously not a good server model.
> >>
> >> I will want the server to support as many users as is possible on any
> >> given machine - and so wasted CPU cycles is something I am trying to
> >> avoid.
> >>
> >> Is the only solution to use a threaded server to let my clients make
> >> their requests and receive a response in the fastest possible time?
> >Snor,
> >
> >The simplest solution is to change your system and put the DB on the
> >same machine thus greatly reducing the time it takes for each DB query
> >to complete (avoid the TCP stack completely).  This way you might not
> >have to change your application logic.
> >
> >If that is not an option, then you are faced with a problem of
> >connecting a threaded programming model with an event based model
> >(twisted and and such). So your job is to interface the two. In other
> >words make the event based model see the threaded DB access as event
> >based. And the DB driver to see the event-based system as threaded. So
> >in your event dispatcher you could add events like db_request_finished
> >then when a connection is requested to the DB, a callback will be
> >supplied. The connection will take place in its own thread, then when
> >it is finished it will put the db_request_finished and the respective
> >callback function on the event queue. I am not sure how to integrate
> >that into the Twisted event dispatcher... perhaps this class is the
> >answer?:
> >http://twistedmatrix.com/documents/current/api/twisted.python.dispatch.EventDispatcher.html
>
> Note, however:
>
> >>> from twisted.python import dispatch
> __main__:1: DeprecationWarning: Create your own event dispatching mechanism, twisted.python.dispatch will soon be no more.
>
> Take a look at <http://twistedmatrix.com/documents/current/api/twisted.enterprise.adbapi.html>.
> 
> Jean-Paul