Turning off Autoflush in SQLAlchemy

[kindly]

David Raznik: I propose we remove autoflush by default in ckan. It caused a lot of bugs on the version upgrade due to its magical behavior.

I have a patch in ​https://bitbucket.org/kindly/ckan/ on branch feature_switch_autoflush_off_by_default.

This change simplifies code. It only took 7 extra flushes/commits to make work and there are over 40 instances that we remove autoflush, so as not to cause error (I have not removed them in the patch yet).

Things to know about using flush:

• Most of the time nothing will change. A commit implies flush.
• You only need to flush if you expect a query to return an object you just saved. i.e if you session.add(obj) and you expect obj to be in a session.query.
• A flush is handy when you want to get the primary key out before you do a commit. i.e session.add(obj); session.flush(); obj.id is now generated.
• You can use them as a limited form of nested transaction.

It increased the performance on the tests by about 5%. There are less flushes altogether so is faster.

I do not see any downsides.

[dread]

Fixed in cset:f2865f43d8ee