Doug Farrell wrote: > I’ve been doing some searching about how to get SQLAlchemy and Twisted > working together in a Twisted application. Though I’ve found a lot of > information, I haven’t seen (or figured out) a good working solution or > definitive answer. The most promising one I’ve run across concerns > running the SQLAlchemy queries in a separate process (rather than a > separate thread) and communicating the queries between the Twisted > application in one process and the SQLAlchemy application in another. > Does anyone have any good pointers, suggestions, ideas, links to how I > might go about setting something like this up?
The best advice I've gotten was from David Bolen; you can find an interchange between him and me on the SA list on October 22 and 23 of last year. The upshot of it is, it shouldn't be a problem to use the SQL level if you're careful to keep the database accesses in a separate thread (and Bolen has done that); using the ORM level, however, can be problematic if you're tempted to access ORM objects in the main thread (since you're not directly in control of when database accesses occur). > Here’s a couple questions that come to mind: > > 1) Would the SQLAlchemy process also be a Twisted application with > all the queries running as deferreds in the main thread, and blocking? There might be value in reworking the SA concepts into a Twisted package, so that the asynchrony is "built in". I haven't heard of any indications of that happening. > 2) How would the Twisted process communicate with the SQLAlchemy > process, using something like XMLRPC, calling methods to perform the > queries? Or would the XMLRPC methods convey something more generic like SQL? Well, Bolen used a dedicated worker thread to do the SA operations (all SQL level), passing functions to it to be executed in that context. He also used a single connection in the thread to do all DB operations. -- Don Dwiggins Advanced Publishing Technology _______________________________________________ Twisted-Python mailing list Twisted-Python@twistedmatrix.com http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python
