[Sqlalchemy-tickets] Issue #3296: raise if isolation_level execution option is used when a Transaction is present; warning in 0.9 (zzzeek/sqlalchemy)

[Mike B. <iss...@bi...>]

New issue 3296: raise if isolation_level execution option is used when a Transaction is present; warning in 0.9
https://bitbucket.org/zzzeek/sqlalchemy/issue/3296/raise-if-isolation_level-execution-option

Mike Bayer:

isolation level settings typically do not work until the next transaction, and at least in the case of Psycopg2 are destructive.  For this reason, the MySQL dialect already implements a COMMIT, and psycopg2 actually *resets* the transaction when you change the level:

```
#!python


>>> import psycopg2
>>> conn = psycopg2.connect(user='scott', dbname='test', password='tiger', host='localhost')
>>> cursor = conn.cursor()
>>> cursor.execute("create table foo (id integer)")
>>> cursor.execute("insert into foo (id) values (1)")
>>> cursor.close()
>>> from psycopg2 import extensions
>>> conn.set_isolation_level(extensions.ISOLATION_LEVEL_SERIALIZABLE)
>>> cursor = conn.cursor()
>>> cursor.execute("select * from foo")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
psycopg2.ProgrammingError: relation "foo" does not exist
LINE 1: select * from foo
                      ^


```

huge warning is needed and definitely an exception in 1.0.