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
4.4 KiB
Python
155 lines
4.4 KiB
Python
"""
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Django settings for test_project project.
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Generated by 'django-admin startproject' using Django 2.1.7.
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For more information on this file, see
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https://docs.djangoproject.com/en/2.1/topics/settings/
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For the full list of settings and their values, see
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https://docs.djangoproject.com/en/2.1/ref/settings/
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"""
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from __future__ import annotations
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import os
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# Build paths inside the project like this: os.path.join(BASE_DIR, ...)
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BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
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# Quick-start development settings - unsuitable for production
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# See https://docs.djangoproject.com/en/2.1/howto/deployment/checklist/
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# SECURITY WARNING: keep the secret key used in production secret!
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SECRET_KEY = "dummy"
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# SECURITY WARNING: don't run with debug turned on in production!
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DEBUG = True
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ALLOWED_HOSTS = []
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# Application definition
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INSTALLED_APPS = [
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"django.contrib.admin",
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"django.contrib.auth",
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"django.contrib.contenttypes",
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"django.contrib.sessions",
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"django.contrib.messages",
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"django.contrib.staticfiles",
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"django_migration_linter",
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"tests.test_project.app_add_manytomany_field",
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"tests.test_project.app_add_not_null_column",
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"tests.test_project.app_add_not_null_column_followed_by_default",
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"tests.test_project.app_alter_column",
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"tests.test_project.app_alter_column_drop_not_null",
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"tests.test_project.app_correct",
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"tests.test_project.app_create_table_with_not_null_column",
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"tests.test_project.app_drop_column",
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"tests.test_project.app_drop_table",
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"tests.test_project.app_ignore_migration",
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"tests.test_project.app_rename_column",
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"tests.test_project.app_rename_table",
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"tests.test_project.app_unique_together",
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"tests.test_project.app_data_migrations",
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"tests.test_project.app_make_not_null_with_django_default",
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"tests.test_project.app_make_not_null_with_lib_default",
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"tests.test_project.app_create_index_exclusive",
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]
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MIDDLEWARE = [
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"django.middleware.security.SecurityMiddleware",
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"django.contrib.sessions.middleware.SessionMiddleware",
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"django.middleware.common.CommonMiddleware",
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"django.middleware.csrf.CsrfViewMiddleware",
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"django.contrib.auth.middleware.AuthenticationMiddleware",
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"django.contrib.messages.middleware.MessageMiddleware",
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"django.middleware.clickjacking.XFrameOptionsMiddleware",
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]
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ROOT_URLCONF = "tests.test_project.urls"
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TEMPLATES = [
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{
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"BACKEND": "django.template.backends.django.DjangoTemplates",
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"DIRS": [],
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"APP_DIRS": True,
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"OPTIONS": {
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"context_processors": [
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"django.template.context_processors.debug",
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"django.template.context_processors.request",
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"django.contrib.auth.context_processors.auth",
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"django.contrib.messages.context_processors.messages",
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]
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},
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}
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]
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WSGI_APPLICATION = "tests.test_project.wsgi.application"
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DATABASES = {
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"default": {
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"ENGINE": "django.db.backends.sqlite3",
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"NAME": os.path.join(BASE_DIR, "db.sqlite3"),
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"TEST": {"DEPENDENCIES": []},
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},
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"sqlite": {
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"ENGINE": "django.db.backends.sqlite3",
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"NAME": "sqlite3",
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"TEST": {"DEPENDENCIES": []},
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},
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"postgresql": {
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"ENGINE": "django.db.backends.postgresql",
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"NAME": "django_migration_linter_test_project",
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"USER": "postgres",
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"PASSWORD": "postgres",
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"HOST": "127.0.0.1",
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"TEST": {"DEPENDENCIES": []},
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},
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"mysql": {
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"ENGINE": "django.db.backends.mysql",
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"NAME": "django_migration_linter_test_project",
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"USER": "root",
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"PASSWORD": "",
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"HOST": "127.0.0.1",
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"TEST": {"DEPENDENCIES": []},
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},
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}
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# Password validation
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AUTH_PASSWORD_VALIDATORS = [
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{
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"NAME": "django.contrib.auth.password_validation.UserAttributeSimilarityValidator"
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},
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{"NAME": "django.contrib.auth.password_validation.MinimumLengthValidator"},
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{"NAME": "django.contrib.auth.password_validation.CommonPasswordValidator"},
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{"NAME": "django.contrib.auth.password_validation.NumericPasswordValidator"},
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]
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# Internationalization
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# https://docs.djangoproject.com/en/2.1/topics/i18n/
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LANGUAGE_CODE = "en-us"
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TIME_ZONE = "UTC"
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USE_I18N = True
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USE_L10N = True
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USE_TZ = True
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# Static files (CSS, JavaScript, Images)
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# https://docs.djangoproject.com/en/2.1/howto/static-files/
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STATIC_URL = "/static/"
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DEFAULT_AUTO_FIELD = "django.db.models.AutoField"
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