There's really two concepts of "isolation level" at play. The "isolation_level" parameter in SQLA is usually linked to database-specific SQL commands that we issue, in the case of PG its "SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL", in sqlite its "PRAMGA read_committed".
But the psycopg2 and pysqlite DBAPIs also support ways to modify the isolation characteristics via connection-specific commands, which also change the DBAPIs behavior a bit. In sqlite its the "autocommit" flag, and psycopg2 its the set_isolation_level() method. In the latter case, we have to use psycopg2's API since psycopg2 itself works against the connection-level settings if it hasn't been told about them (I think it resets them on each command). On a per-connection basis, the difficulty there has always been that we didn't have a nice extensible API with which to apply modifiers to Connection objects. As of 0.6 we do, known as execution_options(), and isolation levels are exactly the kind of function that would be available via execution_options(). So at this point its an unimplemented feature with a fairly clear path. I've placed an initial patch for this in http://www.sqlalchemy.org/trac/ticket/2001 . On Dec 13, 2010, at 10:10 PM, Russell Warren wrote: >> Do other dialects support this, but just not indicate it in the >> documentation? > > On further investigation I see this old ticket: > > http://www.sqlalchemy.org/trac/ticket/443 > > ... which implies it is, in fact, only for PostgreSQL and Sqlite at > the moment. > > I'm also quite interested in setting the isolation level on a per > session/connection basis. However - it seems like the isolation_level > argument to create_engine() sets the isolation level for all managed > connections. I recognize that there may (at least) be some issues > with this based on the connection pooling scheme in use, but is there > a way (even a hack) to do a one-time set of the isolation level to > SERIALIZABLE (for example) for a created session? > > This thread makes it seem like per-session/connection isolation > setting is not as simple as it might seem at first... > http://groups.google.com/group/sqlalchemy-devel/browse_thread/thread/653b6b2f49a940b8 > > And this StackOverflow question makes it seem like it isn't easy to > set the isolation level per session... > http://bit.ly/eG5DUl > > Still digging... > > Russ > > -- > 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. > -- 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.
