OK, I've been going about reforming SA's resource management in the wrong[1] way[2]. I've been trying to refactor the main API of SA's ORM to externalize the resource management. Instead, I should have been working on the internal implementations of objects like Engine, Table, Mapper, ect.
Note: When I talk about resources I mean database connections and objects that manage them (engine, session, etc). It has been mentioned that other frameworks could be built on top of SA. However, I'm predicting that this will not happen until resource management is completely decoupled from SQL construction. Internally, SA uses the thread-local pattern extensively to manage it's resources. This is nice because it takes care of some thread-safety issues, but it's bad because it allows a sloppy coding style that ignores resource management. Thread local is great in some contexts such as web apps where each request is short and discrete (i.e. short enough for a connection to be open for the entire duration of the request processing on the server). But in other environments this will not work at all. It has been pointed out that SA depends on __del__ to clean up its resources. This is very bad. One reason for this is that the Python garbage collector cannot cleanup circularly referenced graphs of objects if __del__ is involved[3]. In an ORM, resource management must be totally explicit and customizable to allow applications to scale in varying environments. Application developers need to be able to control when and how resources are obtained and released. Finally, resource management is orthogonal to the real job of SA, which is to map database data to objects.
From this point forward, I will attempt to refactor resource handling in a way that has less impact on the existing API of SQLAlchemy.
~ Daniel [1] http://article.gmane.org/gmane.comp.python.sqlalchemy.user/1311 [2] http://article.gmane.org/gmane.comp.python.sqlalchemy.user/1329 [3] http://docs.python.org/ref/customization.html#l2h-175 See also: "The trouble with Finalizers" here http://arctrix.com/nas/python/gc/ ------------------------------------------------------- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 _______________________________________________ Sqlalchemy-users mailing list Sqlalchemy-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/sqlalchemy-users
