On Mon, Mar 4, 2013 at 1:34 AM, Aymeric Augustin <aymeric.augus...@polytechnique.org> wrote: > On 4 mars 2013, at 01:07, Shai Berger <s...@platonix.com> wrote: ... >> The use of savepoints in Django apps so far has been very little, as far as >> I know. One point >> I'm unsure of is the interaction of savepoints with cursors, since querysets >> are lazy; so the scenario >> I'm worrirf about is, generally speaking, >> >> @atomic >> def main(): >> for obj in query_with_more_than_100_objects: >> try: >> handle(obj) >> except Bad: >> pass >> >> @atomic >> def handle(obj): >> if good(obj): >> mark_good(obj) >> obj.save() >> else: >> raise Bad(obj) >> >> Will the next (database) fetch after an exception is raised get the right >> objects? >> >> My reading of the Postgresql documentation is that it will do the right >> thing, not so sure about >> the other backends. > > Django currently doesn't support server side cursors — at least on > PostgreSQL, most likely on > other databases too. Accessing the first object loads the entire queryset > instantly.
Actually, the queryset API tries pretty hard to avoid this: https://github.com/django/django/blob/2cd0edaa477b327024e4007c8eaf46646dcd0f21/django/db/models/query.py#L954 It is true that by default, both psycopg and mysqldb do load the full resultset despite using the use of .fetchmany rather than .fetchall https://github.com/django/django/blob/0c82b1dfc48b4870e8fbcfb782ae02cdca821e1f/django/db/models/sql/compiler.py#L765 But this is not django's fault, and I have always wished more drivers would handle streaming results better. In any case, as far as I know, the above code (mixing 2 queries with partial result returns on a single connection) has never worked properly, and I think it will stay equally broken in the new world. I think this could be fairly easily (manually) tested by setting GET_ITERATOR_CHUNK_SIZE to an absurdly low size. Which is to say, +1 from me. -- You received this message because you are subscribed to the Google Groups "Django developers" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-developers+unsubscr...@googlegroups.com. To post to this group, send email to django-developers@googlegroups.com. Visit this group at http://groups.google.com/group/django-developers?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
