Basic question: I have 1 app with multiple processes and threads. Each thread and/or process may end up trying to do something to the database at the same time. What is the solution to threading? How do web frameworks solve it? Is there some inherent design in databases and/or SQLAlchemy that makes this not a actual problem? What do I do if I have 2 separate apps? 3?
I know there has got to be a simple answer to this (after all, every web app has to deal with it), but I can't find anywhere that explains it.... Details: Ok, so let's say I am developing an app with the potential for many threads and processes. The problem is what do I do when each of those threads and processes need to access the database in different ways? read data, change data, etc... The SQLAlchemy documentation says that Sessions are not thread safe and talk about using my own locking mechanisms. However, if I recall correctly, many web frameworks don't even deal with threading issues, yet allow interaction with the database across many threads (http server responses). The PostgreSQL documention on the subject didn't help much: http://www.postgresql.org/docs/8.4/static/mvcc.html except to show that I really don't want to have anything to do with managing the complexities of multiple connections to a database. Pylons docs were equally as vague as the SQLAlchemy docs: essentially that some vague thing is not thread safe in some vague way. Ok, so here's what I can gather. SQLAlchemy is setup like so: 1 Session => 1 DB Connection (from connection pool) => Database * If I setup 2 sessions, that means I will have 2 connections to the database, meaning the database is the one that will handle threading conflicts per what is described here: http://www.postgresql.org/docs/8.4/static/mvcc.html I really don't like relying on that. However, the SQLAlchemy docs suggest making many small Sessions for short interaction with the database. The problem is if I have many threads/processes accessing the DB simultaneously (through separate sessions\connections), then I could get into threading problems working with the database, right? Is the solution to use one single session for the entire application (the application consisting of many processes and threads) and making all my processes communicate with this single session when it needs to do database stuff? Somehow, I have my doubts that it how it should be done -- and even the SQLAlchemy docs say otherwise (although again, very vague about what it is talking about). So, I have 1 app with multiple processes and threads. Each thread and/or process may end up trying to do something to the database at the same time. What is the solution to threading? How do web frameworks solve it? Is there some inherent design in databases and/or SQLAlchemy that makes this not a actual problem? What do I do if I have 2 separate apps? 3? _________________________________________________________________ Your E-mail and More On-the-Go. Get Windows Live Hotmail Free. http://clk.atdmt.com/GBL/go/171222985/direct/01/ -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
