David Cain
0c5519d9dc
Briefly, this check helps prevent a long-running index creation from preventing all reads and writes to a table. This supplements an existing check ================================== There is an existing check, `CREATE_INDEX` which warns about creating indices without the `CONCURRENTLY` argument. It's a helpful check! However, there are some valid reasons to prefer non-concurrent index creation. For example, concurrent index creation may struggle to complete when applied to write-heavy tables (since Postgres will have to make repeated passes on the table to accommodate the new reads since the last round). The danger of `EXCLUSIVE` locks =============================== If you *do* want to create indices nonconcurrently, there is still a **huge footgun** to be aware of -- locks which are held in a transaction are not released until the transaction closes. Dangerous Django defaults ========================= By default, any time you add a new Django field with `db_index=True` or `unique=True`, the automatically generated `Migration` has: - implicit setting of `atomic=True` (transactions are on) - an `ALTER TABLE...ADD COLUMN` call (exclusively locks the table) - a `CREATE INDEX` invocation (*hopefully* quick, due to nullable columns) It's even more dangerous if you combine an `ALTER TABLE` call with `CREATE INDEX` of an existing, non-nullable column. Favor `atomic=False` if you must index ====================================== Index-creating migrations should have few `operations`. Since index creation does not modify row-level data (and only requires locking against writes), there's no reason to use transactions. It's prudent to bypass the default `atomic=True` for index creation.
155 lines
5.0 KiB
Python
155 lines
5.0 KiB
Python
from __future__ import annotations
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import os
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import unittest
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from django.conf import settings
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from django.core.management import call_command
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from django_migration_linter import MigrationLinter
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from tests import fixtures
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class BaseBackwardCompatibilityDetection:
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def setUp(self, *args, **kwargs):
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self.database = next(iter(self.databases))
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self.test_project_path = os.path.dirname(settings.BASE_DIR)
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call_command(
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"migrate",
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"app_unique_together",
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"0002",
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database=self.database,
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)
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self.addCleanup(
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call_command,
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"migrate",
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"app_unique_together",
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database=self.database,
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)
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return super().setUp(*args, **kwargs)
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def _test_linter_finds_errors(self, app=None, commit_id=None):
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linter = self._launch_linter(app, commit_id)
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self.assertTrue(linter.has_errors)
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self.assertNotEqual(linter.nb_valid + linter.nb_erroneous, 0)
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def _test_linter_finds_no_errors(self, app=None, commit_id=None):
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linter = self._launch_linter(app, commit_id)
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self.assertFalse(linter.has_errors)
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self.assertNotEqual(linter.nb_valid + linter.nb_erroneous, 0)
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def _launch_linter(self, app=None, commit_id=None):
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linter = MigrationLinter(
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self.test_project_path,
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database=self.database,
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no_cache=True,
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)
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linter.lint_all_migrations(app_label=app, git_commit_id=commit_id)
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return linter
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# *** Tests ***
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def test_create_table_with_not_null_column(self):
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app = fixtures.CREATE_TABLE_WITH_NOT_NULL_COLUMN
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self._test_linter_finds_no_errors(app)
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def test_detect_adding_not_null_column(self):
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app = fixtures.ADD_NOT_NULL_COLUMN
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self._test_linter_finds_errors(app)
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def test_detect_make_column_not_null_with_django_default(self):
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app = fixtures.MAKE_NOT_NULL_WITH_DJANGO_DEFAULT
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self._test_linter_finds_errors(app)
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def test_detect_make_column_not_null_with_lib_default(self):
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app = fixtures.MAKE_NOT_NULL_WITH_LIB_DEFAULT
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self._test_linter_finds_no_errors(app)
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def test_detect_drop_column(self):
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app = fixtures.DROP_COLUMN
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self._test_linter_finds_errors(app)
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def test_detect_drop_table(self):
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app = fixtures.DROP_TABLE
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self._test_linter_finds_errors(app)
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def test_detect_rename_column(self):
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app = fixtures.RENAME_COLUMN
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self._test_linter_finds_errors(app)
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def test_detect_rename_table(self):
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app = fixtures.RENAME_TABLE
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self._test_linter_finds_errors(app)
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def test_ignore_migration(self):
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app = fixtures.IGNORE_MIGRATION
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self._test_linter_finds_no_errors(app)
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def test_accept_not_null_column_followed_by_adding_default(self):
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app = fixtures.ADD_NOT_NULL_COLUMN_FOLLOWED_BY_DEFAULT
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self._test_linter_finds_no_errors(app)
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def test_detect_alter_column(self):
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app = fixtures.ALTER_COLUMN
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self._test_linter_finds_no_errors(app)
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def test_drop_unique_together(self):
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app = fixtures.DROP_UNIQUE_TOGETHER
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self._test_linter_finds_errors(app)
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def test_accept_alter_column_drop_not_null(self):
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app = fixtures.ALTER_COLUMN_DROP_NOT_NULL
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self._test_linter_finds_no_errors(app)
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def test_accept_adding_manytomany_field(self):
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app = fixtures.ADD_MANYTOMANY_FIELD
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self._test_linter_finds_no_errors(app)
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def test_with_git_ref(self):
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self._test_linter_finds_errors(commit_id="v0.1.4")
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def test_failing_get_sql(self):
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call_command("migrate", "app_unique_together", database=self.database)
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linter = MigrationLinter(database=self.database)
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with self.assertRaises(ValueError):
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linter.get_sql("app_unique_together", "0003")
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class SqliteBackwardCompatibilityDetectionTestCase(
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BaseBackwardCompatibilityDetection, unittest.TestCase
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):
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databases = ["sqlite"]
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def test_accept_not_null_column_followed_by_adding_default(self):
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app = fixtures.ADD_NOT_NULL_COLUMN_FOLLOWED_BY_DEFAULT
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self._test_linter_finds_errors(app)
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def test_detect_make_column_not_null_with_django_default(self):
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app = fixtures.MAKE_NOT_NULL_WITH_DJANGO_DEFAULT
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self._test_linter_finds_errors(app)
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def test_detect_make_column_not_null_with_lib_default(self):
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# The 'django-add-default-value' doesn't handle sqlite correctly
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app = fixtures.MAKE_NOT_NULL_WITH_LIB_DEFAULT
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self._test_linter_finds_errors(app)
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class MySqlBackwardCompatibilityDetectionTestCase(
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BaseBackwardCompatibilityDetection, unittest.TestCase
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):
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databases = ["mysql"]
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class PostgresqlBackwardCompatibilityDetectionTestCase(
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BaseBackwardCompatibilityDetection, unittest.TestCase
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):
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databases = ["postgresql"]
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def test_detect_alter_column(self):
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app = fixtures.ALTER_COLUMN
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self._test_linter_finds_errors(app)
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def test_create_index_exclusive(self):
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app = fixtures.CREATE_INDEX_EXCLUSIVE
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self._test_linter_finds_errors(app)
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