django.db.transaction.atomic() leaks savepoints on exception

[hyperair@…]

When savepoints are rolled back after an exception in a transaction.atomic() block, the savepoint is leaked. Specifically, "ROLLBACK TO SAVEPOINT xx" is done, but not "RELEASE SAVEPOINT xx". The savepoint ID is then thrown away by Django and leaked.

See ​http://www.postgresql.org/docs/9.1/static/sql-release-savepoint.html and ​http://www.postgresql.org/docs/9.1/static/sql-rollback-to.html for more information.

When spinning in a get_or_create() loop in a single transaction, this has the potential to max out the shared memory of the PostgreSQL instance resulting in this:

File "/usr/lib/python2.7/dist-packages/django/db/models/manager.py", line 157, in create

return self.get_queryset().create(kwargs)

File "/usr/lib/python2.7/dist-packages/django/db/models/query.py", line 319, in create

obj.save(force_insert=True, using=self.db)

File "/usr/lib/python2.7/dist-packages/django/db/models/base.py", line 545, in save

force_update=force_update, update_fields=update_fields)

File "/usr/lib/python2.7/dist-packages/django/db/models/base.py", line 573, in save_base

updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)

File "/usr/lib/python2.7/dist-packages/django/db/models/base.py", line 654, in _save_table

result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)

File "/usr/lib/python2.7/dist-packages/django/db/models/base.py", line 687, in _do_insert

using=using, raw=raw)

File "/usr/lib/python2.7/dist-packages/django/db/models/manager.py", line 232, in _insert

return insert_query(self.model, objs, fields, kwargs)

File "/usr/lib/python2.7/dist-packages/django/db/models/query.py", line 1511, in insert_query

return query.get_compiler(using=using).execute_sql(return_id)

File "/usr/lib/python2.7/dist-packages/django/db/models/sql/compiler.py", line 898, in execute_sql

cursor.execute(sql, params)

File "/usr/lib/python2.7/dist-packages/django/db/backends/util.py", line 69, in execute

return super(CursorDebugWrapper, self).execute(sql, params)

File "/usr/lib/python2.7/dist-packages/django/db/backends/util.py", line 53, in execute

return self.cursor.execute(sql, params)

File "/usr/lib/python2.7/dist-packages/django/db/utils.py", line 99, in exit

six.reraise(dj_exc_type, dj_exc_value, traceback)

File "/usr/lib/python2.7/dist-packages/django/db/backends/util.py", line 53, in execute

return self.cursor.execute(sql, params)

django.db.utils.OperationalError: out of shared memory
HINT: You might need to increase max_locks_per_transaction.

[Chow Loong Jin <hyperair@…>]

Patch to call savepoint_commit after savepoint_rollback in Atomic.exit