On Jan 11, 2009, at 11:40 AM, Darren Govoni wrote:
> > Sorry for the haze. I'm using PostgreSQL and am checking their docs on > isolation to see that it is consistent with SA. > > but here is a simplified example. > > I have 2 rows in the database with 1 column "FOO". Both rows have a > NULL > value for column "FOO". > > Two programs, A and B. They are the same program. > > > I have a query that: selects for update, all rows with FOO=NULL, limit > 1. This will block all other processes attempting the same query. > > > A goes first and selects for update. B thus blocks. Both are looking > for > 1 row, FOO=NULL. > > A query returns 1 row. Inside the transaction. A updates that row to > FOO=A. B is still waiting. Only 1 row is updated, because 1 is > returned > from the select. I use session.add(row) to simply re-add the mapped > object after changing the value. > > A commits its change to 1 row. The second row is still FOO=NULL. > > B unblocks. B returns 0 results. > > A, B exit. > > Re-run B. > > B finds 1 row where FOO=NULL and sets FOO=B. > > B exits. > > Does that help clarify? yeah I understood all that (except for the session.add(row) part, which doesn't seem related). And no, it does not sound correct, in that when B is unblocked into the transaction, it should see the same thing as if it had just been run completely after the A transaction were committed. in any case you should view the SQL logs (echo=True) to see what the conversation is saying. If that all looks as expected, open up two postgres consoles and try the same conversation manually. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@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 -~----------~----~----~----~------~----~------~--~---
