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Fixed #24743, #24745 -- Optimized migration plan handling

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The change partly goes back to the old behavior for forwards migrations
which should reduce the amount of memory consumption (#24745). However,
by the way the current state computation is done (there is no
`state_backwards` on a migration class) this change cannot be applied to
backwards migrations. Hence rolling back migrations still requires the
precomputation and storage of the intermediate migration states.

This improvement also implies that Django does not handle mixed
migration plans anymore. Mixed plans consist of a list of migrations
where some are being applied and others are being unapplied.

Thanks Andrew Godwin, Josh Smeaton and Tim Graham for the review as well
as everybody involved on the ticket that kept me looking into the issue.
This commit is contained in:
Markus Holtermann 2015-08-27 09:49:35 +10:00
parent 186eb21dc1
commit 5aa55038ca
7 changed files with 184 additions and 27 deletions
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59
tests/migrations/test_executor.py
View file

@ -1,5 +1,6 @@
from django.apps.registry import apps as global_apps
from django.db import connection
from django.db.migrations.exceptions import InvalidMigrationPlan
from django.db.migrations.executor import MigrationExecutor
from django.db.migrations.graph import MigrationGraph
from django.db.migrations.recorder import MigrationRecorder
@ -145,6 +146,64 @@ class ExecutorTests(MigrationTestBase):
executor.recorder.record_unapplied("migrations", "0002_second")
executor.recorder.record_unapplied("migrations", "0001_initial")
@override_settings(MIGRATION_MODULES={
"migrations": "migrations.test_migrations",
"migrations2": "migrations2.test_migrations_2_no_deps",
})
def test_mixed_plan_not_supported(self):
"""
Although the MigrationExecutor interfaces allows for mixed migration
plans (combined forwards and backwards migrations) this is not
supported.
"""
# Prepare for mixed plan
executor = MigrationExecutor(connection)
plan = executor.migration_plan([("migrations", "0002_second")])
self.assertEqual(
plan,
[
(executor.loader.graph.nodes["migrations", "0001_initial"], False),
(executor.loader.graph.nodes["migrations", "0002_second"], False),
],
)
executor.migrate(None, plan)
# Rebuild the graph to reflect the new DB state
executor.loader.build_graph()
self.assertIn(('migrations', '0001_initial'), executor.loader.applied_migrations)
self.assertIn(('migrations', '0002_second'), executor.loader.applied_migrations)
self.assertNotIn(('migrations2', '0001_initial'), executor.loader.applied_migrations)
# Generate mixed plan
plan = executor.migration_plan([
("migrations", None),
("migrations2", "0001_initial"),
])
msg = (
'Migration plans with both forwards and backwards migrations are '
'not supported. Please split your migration process into separate '
'plans of only forwards OR backwards migrations.'
)
with self.assertRaisesMessage(InvalidMigrationPlan, msg) as cm:
executor.migrate(None, plan)
self.assertEqual(
cm.exception.args[1],
[
(executor.loader.graph.nodes["migrations", "0002_second"], True),
(executor.loader.graph.nodes["migrations", "0001_initial"], True),
(executor.loader.graph.nodes["migrations2", "0001_initial"], False),
],
)
# Rebuild the graph to reflect the new DB state
executor.loader.build_graph()
executor.migrate([
("migrations", None),
("migrations2", None),
])
# Are the tables gone?
self.assertTableNotExists("migrations_author")
self.assertTableNotExists("migrations_book")
self.assertTableNotExists("migrations2_otherauthor")
@override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations"})
def test_soft_apply(self):
"""